19 Zn(s) + CuSO4(aq) → 4.4 Heat of Neutralisation A 4.6 °C C 9.1 °C
Cu(s) + ZnSO4(aq); B 6.8 °C D 13.5 °C
ΔH = –218 kJ mol–1
23 Which of the following 27 The heat of neutralisation
What is the minimum mass of
zinc required in order that its neutralisation reactions releases between hydrochloric acid and
reaction with excess copper(II)
sulphate solution produces ’04 the least heat? sodium hydroxide is –57 kJ
10.9 kJ of heat?
[Relative atomic mass: Zn, 65.4] A 1 mol of HCl(aq) + mol–1. What is the heat energy
A 1.7 g
B 3.3 g B 1 mol ooooNffffHCCNK3O(HHHaH333qCC(()aOOaqqOO))HH + released, when 500 cm3 of
C 5.0 g C 1 mol +
D 6.6 g 1 mol 2 mol dm–3 sulphuric acid
1 mol
1 mol reacts with excess potassium
D 1 mol of HCl(aq) + hydroxide?
A –0.5 3 57 kJ
1 mol of NaOH(aq) B –57 kJ
C –2 3 57 kJ
24 When 40 cm3 of 0.1 mol dm–3 D –4 3 57 kJ
20 When 4.8 g of magnesium is hydrochloric acid is mixed with 28 The information that must be
added to 50 cm3 of 2.0 mol 10 cm3 of 0.1 mol dm–3 sodium obtained in an experiment
’07 dm–3 copper chloride solution, hydroxide solution, the rise in to determine the heat of
the temperature of the mixture temperature is t °C. What is the neutralisation are
increases by 4.0 °C. What is rise in temperature when 20 cm3 I volumes of acids and alkalis.
the heat of reaction in this of 0.1 mol dm–3 hydrochloric acid II concentrations of acids and
4 experiment? reacts with 30 cm3 of 0.1 mol alkalis.
[Specific heat capacity of dm–3 sodium hydroxide solution? III maximum rise in temperature.
solution = 4.2 J g–1 °C–1; relative A —12 t °C C 2t °C IV degree of dissociation of
atomic mass of Mg = 24] B t °C D 4t °C acids and alkalis.
A –0.42 J mol–1 A I and III only
B –0.84 J mol–1 25 When 50 cm3 of 1.5 mol dm–3 B II and IV only
C –4.20 kJ mol–1 C I, II and III only
D –8.4 kJ mol–1 HCl is added to 100 cm3 of D I, II, III and IV
21 A student wanted to determine 1.5 mol dm–3 sodium hydroxide 29 Which of the following reactions
the heat of displacement for the solution, x kJ of heat is produced. will produce the same amount
reaction When 45 cm3 of sulphuric acid of heat of neutralisation?
MMggS(sO)4+(aqC)uS+OC4(ua(qs)) → is added to 100 cm3 of 1.5 mol Reaction I Reaction II
Which of the following dm–3 sodium hydroxide, the same A HNO3(aq) + H2SO4(aq) +
NaOH(aq) KOH(aq)
measurements is not required amount of heat is produced.
B HNO3(aq) + HNO3(aq) +
for the experiment? What is the concentration of NaOH(aq) NH3(aq)
A Temperature of CuSO4 solution sulphuric acid? C HCl(aq) + C+HN3CHO3(OaqH)(aq)
B Volume of CuSO4 solution A 0.2 mol dm–3 NH3(aq)
C Concentration of CuSO4 B 0.4 mol dm–3
solution C 0.8 mol dm–3
D 1.5 mol dm–3
D Mass of magnesium reacted 26 D HCl(aq) + +CHN3CaOOHO(Ha(qa)q)
NaOH(aq)
22 Consider the following reactions. Based on the energy level 4.5 Heat of Combustion
diagram given above, what is
I NaOH(s) → NaOH(aq) the temperature rise when 30 The combustion of 3.6 g of fuel
’09 II NH4Cl(s) → NH4Cl(aq) 25 cm3 of 1 mol dm–3 H2SO4 X increases the temperature of
III NaHCO3(s) + HCl(aq) → is mixed with 50 cm3 of 1 mol 500 cm3 of water by 22.8 °C.
dm–3 sodium hydroxide solution? What is the temperature rise if the
NaCl(aq) + H2O(l) + CO2(g) [Specific heat capacity of combustion of 7.2 g of fuel X is
IV Mg(s) + FeSO4(aq) → solution = 4.2 J g–1 °C–1; density used to heat up 1.0 dm3 of water?
of solution = 1 g dm–3] A 11.4 °C
MgSO4(aq) + Fe(s) B 14.2 °C
Identify the energy-releasing C 22.8 °C
D 28.4 °C
reactions.
A I and II
B II and III
C III and IV
D I and IV
Thermochemistry 494
31 The results of an experiment to 33 C4H9OH(l) + 6O2(g) → B – —41 2220 kJ
determine the heat change for 4CO2(g) + 5H2O(l);
ΔH = –2670 kJ mol–1
’06 the combustion of propanol, C – _13__ 2220 kJ
C3H7OH, are shown below. Based on the thermochemical
Volume of water in the copper equation given above, what is D – 4 3 2220 kJ
container = 300 cm3 the mass of butanol needed for
Initial temperature of water combustion in order to produce 36 The heat of combustion of a
= 28.5 °C 80 kJ of heat?
Final temperature of water [Relative atomic mass: C, 12; fuel, X is –273 kJ mol–1. What is
= 69.0 °C H, 1; O, 16]
What is the heat released by the A 2.22 g the maximum temperature rise
combustion of propanol? B 4.44 g
[Specific heat capacity of water C 6.66 g when 100 cm3 of water is heated
= 4.2 J g–1 °C–1; assume that D 8.88 g
1 cm3 of water is equal to 1 g] by the combustion of 0.80 g of
A 25.20 kJ
B 34.65 kJ X? [Relative molecular mass of
C 51.03 kJ
D 86.94 kJ X = 40; specific heat capacity of
32 The diagram shows the water = 4.2 J g–1 °C–1]
arrangement of apparatus used
for determining the heat of A 6 °C C 13 °C
combustion of methanol.
B 9 °C D 15 °C
Which of the following steps
must be taken to ensure 34 The heat of combustion of 37 The equation for the combustion 4
that the experimental results alcohols increases in the order: of ethanol in excess oxygen is
obtained are accurate? ethanol < propanol < butanol
I Replace the glass beaker with Which of the following ’07 shown below.
statements explain the trend?
a metal container. C2H5OH(l) + 3O2(g) →
II Stir the water continuously. I The number of carbon atoms 2CO2(g) + 3H2O(l);
III Remove the wire gauze. per molecule increases.
IV Place the spirit lamp closer to ΔH = –1371 kJ mol–1
II The number of hydrogen
the water. atoms per molecule Which of the energy level
A III and IV only increases. diagrams represents the
B I, II and IV only reaction?
C II, III and IV only III The number of oxygen atoms A
D I, II, III and IV per molecule increases
IV The chemical bonds in the B
molecule become stronger.
A I and II only
B III and IV only
C II and III only
D I, II and IV only
35 The heat of combustion of
propane is –2220 kJ mol–1. C
C3H8(g) + 5O2(g) →
3CO2(g) + 4H2O(l);
ΔH = –2220 kJ mol–1
How much heat energy is evolved
D
when 11 g of carbon dioxide
is produced from the complete
combustion of propane?
A – —14 —31 2220 kJ
495 Thermochemistry
Structured Questions Diagram 2
1 Two experiments are carried out to determine the Which of these polystyrene beakers should be
heat of displacement of copper by zinc.
used? Why? [2 marks]
Experiment 1
A heating element is immersed in copper(II) sulphate 2 The apparatus set-up as shown below is used to
solution and 1.0 kJ of heat energy is supplied. determine the heat of combustion of ethanol. The
copper container contains 100 cm3 of water.
Experiment II
3.27 g of zinc powder is added to 200 cm3 of
copper(II) sulphate solution (in excess).
In both these experiments,
• the copper(II) sulphate solution is placed in a
polystyrene beaker,
• the initial temperature of copper(II) sulphate is
30.4 °C.
Diagram 1 shows the thermometer readings for the
maximum temperature reached in Experiments I
and II.
4
Diagram 1 The results of the experiment are shown below.
(a) What is meant by heat of displacement of copper Mass of ethanol + lamp before 150.38
by zinc? [1 mark] combustion (g)
149.83
(b) Explain why polystyrene beaker is used in Mass of ethanol + lamp after
Experiments I and II. [1 mark] combustion (g) 30.0
61.5
(c) Calculate the rise in temperatures in Experiments Initial temperature of water (°C)
I and II. [2 marks] Highest temperature of water (°C)
(d) (i) State two observations in Experiment II. (a) What is meant by heat of combustion of
[2 marks] ethanol? [1 mark]
(ii) State one precaution that must be taken
while carrying out Experiment II. [1 mark]
(e) (i) Calculate the heat energy change in (b) Write a chemical equation for the complete
Experiment II.
combustion of ethanol. [1 mark]
(ii) Calculate the number of moles of copper
metal formed in Experiment II. (c) (i) Calculate the number of moles of ethanol
(iii) With reference to your answers in (i) and used in the experiment. [2 marks]
(ii), calculate the heat of displacement of
copper by zinc. (ii) Calculate the heat released in the
[Specific heat capacity of solution: 4.2 J
g–1 °C–1; density of solution: 1.0 g cm–3; experiment. [1 mark]
relative atomic mass: Zn, 65.4]
[3 marks] [Specific heat capacity of water = 4.2 J g–1
°C–1; density of water = 1 g cm–3]
(iii) Calculate the heat of combustion of
ethanol. [1 mark]
(f) Experiment II can be carried out by using (d) The theoretical heat of combustion of ethanol is
polystyrene beaker A or polystyrene beaker B –1371 kJ mol–1. Give two reasons why the heat
(Diagram 2).
of combustion obtained from this experiment is
different from the theoretical value. [2 marks]
Thermochemistry 496
3 (a) Experiment I was carried out to determine the heat of neutralisation between sulphuric acid and [1 mark]
potassium hydroxide. The experimental result shows that the heat of neutralisation is –57 kJ mol–1. [1 mark]
(i) What is meant by heat of neutralisation?
(ii) Draw the energy level diagram for the reaction.
(b) In Experiment II, 50 cm3 of 1 mol dm–3 nitric acid is added to 50 cm3 of 1 mol dm–3 ammonia
solution in a polystyrene cup. The initial temperatures of the acid and alkali are measured.
The mixture is stirred slowly and the maximum temperature of the mixture is recorded. The results
of the experiment are shown below.
Initial temperature of nitric acid = 28.2 °C
Initial temperature of ammonia solution = 28.2 °C
The maximum temperature = 34.2 °C
[The specific heat of solution = 4.2 J g–1 °C–1; Density of solution = 1 g cm–3] [2 marks]
(i) State two precautions that must be taken when carrying out the experiment. [2 marks]
[3 marks]
(ii) Calculate the number of moles of water molecules produced. [2 marks]
(iii) Calculate the heat of neutralisation between nitric acid and ammonia solution. [1 mark]
(c) Explain why the heat of neutralisation obtained in Experiment I is different from that in Experiment II.
(d) Predict the temperature change if Experiment II is repeated by adding 100 cm3 of hydrochloric acid
to 100 cm3 of 1 mol dm–3 ammonia solution.
Explain your answer.
4 (a) Diagram 3 shows the apparatus set-up for Experiments I, II and III and the readings of the initial 4
temperature and the highest or lowest temperature in each experiment.
Diagram 3
(i) Identify the exothermic and endothermic reaction in these reactions. [2 marks]
(ii) Three substances are used for this experiment: ammonium sulphate, sodium hydrogen [2 marks]
[1 mark]
carbonate and sodium hydroxide. Match these substances with X, Y and Z. [2 marks]
(iii) Write the equation for Experiment III.
(iv) Draw an energy level diagram for the reaction in Experiment I. [1 mark]
[2 marks]
(b) When 25.0 cm3 of 0.5 mol dm–3 silver nitrate solution is poured into 25.0 cm3 of 0.5 mol dm–3 of
sodium chloride solution, the temperature increases by 3 °C. [2 marks]
(i) Calculate the heat change in this experiment. [Specific heat capacity of solution is 4.2 J g–1 °C–1;
Density of solution is 1.0 g cm–3]
(ii) Calculate the heat of precipitation of silver chloride for this experiment.
(iii) The experiment is repeated using 25.0 cm3 of 0.5 mol dm–3 silver nitrate solution to react
with 25.0 cm3 of 0.5 mol dm–3 hydrochloric acid.
Predict the temperature change in this experiment. Give a reason for your prediction.
497 Thermochemistry
Essay Questions
1 (a) Describe one experiment to determine the (i) What is the fuel value of propanol.
(ii) State two main factors that must be
heat of precipitation of lead(II) chloride. In your
considered when choosing a fuel. [3 marks]
answer, show the workings in your calculation,
assumptions made and the energy level diagram 2 (a) Describe one experiment to determine the
for the precipitation of lead(II) chloride. heat of neutralisation between dilute sulphuric
[12 marks] acid and sodium hydroxide solution. Show the
(b) The heats of combustion of methanol and workings in your calculation. [12 marks]
ethanol are –715 kJ mol–1 and –1371 kJ mol–1
respectively. State two similarities between the (b) Explain why the heat of neutralisation between
combustion of methanol and the combustion of hydrochloric acid and sodium hydroxide is the
ethanol. Explain why the heat of combustion of same as the heat of neutralisation between nitric
ethanol is different from the heat of combustion acid and potassium hydroxide solution. [4 marks]
of methanol. [5 marks]
(c) The reaction between nitrogen and hydrogen to
(c) The heat of combustion of propanol is –2010 kJ form ammonia is an exothermic reaction. Explain
mol–1.
this observation in terms of bond breaking and
bond forming. [4 marks]
4 Experiments
1 Diagram 1 shows two experiments carried out to (b) Construct a table to tabulate the results of
determine the heat of neutralisation.
Experiments I and II. [3 marks]
’06 Experiment I: Reaction between 25 cm3 of methanoic
acid, HCOOH, 2.0 mol dm–3 and 25 cm3 of sodium (c) State three observations in Experiment I other
hydroxide solution, NaOH, 2.0 mol dm–3.
than the change in temperature. [3 marks]
45
(d) State one hypothesis for both experiments.
Diagram 1
Initial temperature of the mixture = … … … °C [3 marks]
Highest temperature of the mixture = … … … °C
Increase in temperature = … … … °C (e) State the constant variables in this experiment.
Experiment II: Reaction between 25 cm3 of [3 marks]
hydrochloric acid, HCl, 2.0 mol dm–3 and 25 cm3 of
sodium hydroxide solution, NaOH, 2.0 mol dm–3. (f) Based on the temperatures in Experiment I,
predict the rise in temperature in Experiment II.
[3 marks]
(g) (i) Define heat of neutralisation. [3 marks]
(ii) Calculate the heat of neutralisation for
the reaction between methanoic acid and
sodium hydroxide. [3 marks]
(Specific heat capacity of solution = 4.2 J
g–1 °C–1; density of solution = 1.0 g cm–3)
2 A student bought two canisters of fuels (brand X and
brand Y) for camping. It is found that 200 g of fuel
of brand X can boil 200 cm3 of water in 12 minutes,
whereas 200 g of fuel of brand Y can boil 200 cm3
of water in 20 minutes.
With reference to the above observation, you are
asked to plan an experiment to compare the fuel
values (heat of combustion expressed in kJ g–1) of
fuel X and fuel Y.
Initial temperature of the mixture = T1 °C Your planning should include the following aspects:
Highest temperature of the mixture = T2 °C
Increase in temperature = T3 °C (a) Aim of experiment
(b) All the variables
(a) Write the initial and the highest temperature (c) Statement of the hypothesis
of the solution and the rise of temperature for (d) List of substances and apparatus
Experiment I. (e) Procedure of the experiment
[3 marks] (f) Tabulation of data [17 marks]
Thermochemistry 498
5CHAPTER FORM 5
THEME: Production and Management of Manufactured Chemicals
Chemicals for Consumers
SPM Topical Analysis
Year 2008 2009 2010 2011
Paper 1 2 31 2 31 2 31 2 3
Section ABC ABC ABC ABC
Number of questions 3 – 1 – – 2 – – – – 1 – —12 – – 2 – 1 – –
ONCEPT MAP
CHEMICALS FOR CONSUMERS
Cleansing agents Food additives Medicine
Soap Detergent • Preservative: sodium nitrite Traditional medicine Modern
Palm oil Preparation of sodium • Antioxidant: ascorbic acid • derived from plants medicine
+ alkyl sulphate • Flavouring agent: MSG
NaOH • Stabiliser and thickening agent: and animals
R – O – SO3H
↓ + gelatin and acacia gum • Analgesic: aspirin, paracetamol and
Soap • Dyes: azo compound and triphenyl codeine
NaOH
+ compound • Antibiotic: penicillin; streptomycin
Glycerol ↓ • Psychotherapeutic medicine
ROSO3–Na+ + H2O
– stimulant
Cleansing action of soap and Effects on health – antipsychotic
detergent • Allergy – antidepressant
• The ‘head’ (hydrophilic) • Cancer causing
• Brain damage Side effects
dissolves in water • Hyperactivity Aspirin: causes stomach bleeding
• The ‘tail’ (hydrophobic) dissolves Penicillin: allergy
Additives in detergents Psychotherapeutic medicine: addiction
in greasy dirt • Builders (sodium tripolyphosphate):
• Wetting action
• Emulsification to soften hard water
• Whitening agent (sodium perborate):
Effectiveness of soap and
detergent for making clothes white
• Soap is not effective in hard • Biological enzyme: decomposes protein
water or acidic water stains such as blood and food
• Detergents are effective in both
hard water and acidic water
5.1 Soaps and Detergents Fatty acid Example of soap
C17H33COOH C17H33COO–K+
Soaps Oleic acid Potassium oleate
C17H35COOH C17H35COO–K+
SPM 1 Cleansing agents are chemical substances used Stearic acid Potassium stearate
’04/P2 to remove grease and dirt.
2 There are two types of cleansing agents: 2 Soap is produced by the reaction between sodium
hydroxide or potassium hydroxide with animal
(a) Soaps (b) Detergents fats or vegetable oils. This reaction is known
as saponification.
The History of Soap Manufacturing
3 Fats and vegetable oils are large, naturally
1 Soaps have been used for more than 3000 occurring ester molecules. When fats or oils
are boiled with concentrated alkalis, such as
years. It was recorded that the Babylonians sodium hydroxide or potassium hydroxide,
saponification occurs and the ester molecules
were making soap around 2800 B.C. are broken down into soap and glycerol.
2 In ancient times, soaps were made from ashes
of plants which contain sodium carbonate and
potassium carbonate. The ashes were boiled
with lime (calcium oxide) to produce caustic Fats and oils + NaOH(aq) or
(natural ester) KOH(aq) (alkali)
potash (potassium hydroxide). Caustic potash is
5 then boiled with animal fats to produce soap.
(a) Ash + lime ⎯b⎯oil→ caustic potash Glycerol (an alcohol Soap (RCOONa
with three –OH groups) or RCOOK)
(K2CO3) (CaO) (KOH) +
(b) Caustic potash + animal fats ⎯b⎯oil→ soap 4 Saponification is the alkaline hydrolysis of
esters using alkali solutions. From a chemical
3 In 1816, the French chemist Michel Chevreul aspect, soaps are sodium salts or potassium
(1786 – 1889) discovered that animal fats salts of long chain fatty acids (with 12 to 18
are composed of fatty acids and glycerol. carbon atoms per molecule).
This discovery contributed to the rapid
development of the soap and candle industry. 5 Glyceryl tristearates are naturally occurring esters
commonly found in animal fats and vegetable
4 In 1861, the Belgian chemist Ernest Solvay oils. When the ester is boiled with concentrated
(1838–1922) discovered the process to make sodium hydroxide solution, saponification
soda (sodium carbonate) from common salt (alkaline hydrolysis) occurs and a mixture of
(sodium chloride) and calcium carbonate. sodium stearate (soap) and glycerol is obtained.
This process is known as the Solvay Process
which produces sodium carbonate which is O
used for making glass, soaps and detergents. i
SPM CH2– C – O – C17H35
Preparation of Soap by Saponification ⎮⎮ Oi
’08/P1, CH– C – O – C17H35 + 3Na OH concentrated
’09/P1, NaOH
’10/P1 ⎮ O
⎯⎯b⎯oi⎯l ⎯→
1 (a) Soap is a chemical used as a cleansing
agent to remove grease and dirt. ⎮ i
(b) Soaps are sodium or potassium salts of CH2– C – O – C17H35
glyceryl tristearate (in fats and oils)
long chain fatty acids with 12 to 18 carbon
atoms per molecule. The general formula of
soap is RCOO–Na+ or RCOO–K+ (Table 5.1). CH2 – OH
Table 5.1 Examples of soap ⎮
Fatty acid Example of soap CH – OH + 3C17H35COO–Na+
⎮ soap
⎮ (sodium stearate)
C15H31COOH C15H31COO–Na+
Palmitic acid Sodium palmitate CH2 – OH
glycerol
Chemicals for Consumers 500
6 The soap produced can be precipitated by 8 Soaps produced from sodium hydroxide are
adding common salt (sodium chloride) to the hard whereas soaps produced from potassium
reaction mixture. hydroxide are soft.
Sodium chloride reduces the solubility of
soap in aqueous solution and causes the soap 9 Animal fats (tallow) from cows and vegetable
to be precipitated out. oils (such as palm oil or olive oil) are used for
making soap.
7 The properties of soap depend on
(a) the type of alkali used for saponification, 10 Activity 5.1 describes the method for making
(b) the type of animal fats or vegetable oils soap by the saponification process.
used.
To prepare soap
Apparatus Beaker, measuring cylinder, glass rod, Bunsen burner, filter funnel, filter paper, wire gauze,
spatula and tripod stand.
Materials 5 mol dm–3 sodium hydroxide solution, sodium chloride solution, palm oil, olive oil, corn oil
and peanut oil.
Procedure Activity 5.1 5
(A) Preparation of soap
1 Using a small (100 cm3) measuring cylinder, 10 cm3 of palm oil is measured out into a beaker.
2 Using a large (250 cm3) measuring cylinder, 50 cm3 of concentrated (5 mol dm–3) sodium hydroxide solution
is measured out and poured into the palm oil in the beaker.
3 The mixture is heated until boiling (Figure 5.1 (a)). The solution is stirred with a glass rod throughout the
experiment.
4 The boiling is continued for about 5 minutes until the layer of oil disappears.
5 The Bunsen flame is then turned off and the reaction mixture is left to cool.
(B) To separate soap from the reaction mixture
1 Three to four spatula of sodium chloride is dissolved in about 100 cm3 of water.
2 The salt solution is then added to the soap solution obtained in Section A. The mixture is boiled again for
about 5 minutes (Figure 5.1 (b)).
Figure 5.1 Preparation of soap
3 When the mixture is cooled, a white precipitate is formed, which floats on the surface of the mixture.
4 The mixture is filtered (Figure 5.1 (c)) and washed with distilled water to remove excess alkali and salt.
5 A small amount of the residue on the filter paper is examined by (a) rubbing it on the hand, (b) shaking it
with water in a boiling tube. The observations are recorded.
6 The experiment is repeated using olive oil, corn oil and peanut oil.
501 Chemicals for Consumers
Results Observation boiling the solution again. This process is called
salting out.
Test Soapy (slippery) feel 3 The salting out process occurs because sodium
(a) Rubbed on the hand chloride reduces the solubility of soap in water
(b) Shaken with water A lot of foam is and causes it to be precipitated.
produced 4 The precautionary step in this experiment is to
control the flame of the Bunsen burner. This is
Discussion because boiling a mixture of palm oil with sodium
hydroxide solution produces a lot of froth.
1 The white residue on the filter paper is soap
because it has a slippery feel and produces foam Conclusion
when shaken with water.
Soaps can be prepared from vegetable oils and
2 The soap produced in Section A can be precipitated concentrated sodium hydroxide solution by
from the solution by adding sodium chloride and saponification.
The Structure of Soap Molecule ‘tail’. The ‘head’ is negatively-charged and the
5 1 When soap is dissolved in water, it will ‘tail’ is a long hydrocarbon chain.
dissociate and produce sodium ions and
carboxylate ions (RCOO–). For example, O
sodium stearate (soap) dissolves in water to
form sodium ions and stearate ions. 3 The ‘head’ contains the –C–O– ion which
C17H35COONa(s) + water → C17H35COO–(aq) dissolves readily in water (hydrophilic) but
sodium stearate stearate ions does not dissolve in oil. Conversely, the ‘tail’
contains a long hydrocarbon chain which
+ Na+(aq) is insoluble in water (hydrophobic) but
dissolves readily in oil.
2 The stearate ions take part in the removal of 4 Soaps made from palmitic acid are known
dirt but the sodium ions do not. The stearate as sodium palmitate. Figure 5.2 shows the
ion consists of two parts: the ‘head’ and the
structure of the palmitate ion (C15H31COO–).
SPM
’04/P1
’05/P2
Figure 5.2 The structure of a palmitate ion
5 Figure 5.3 (a) shows the molecular model of the palmitate ion and Figure 5.3 (b) shows
the simple representation of the structure of the palmitate ion.
Chemicals for Consumers Figure 5.3 The palmitate ion
502
Detergents SPM 3 The equations for the preparation of sodium
’08/P1 lauryl sulphate is shown below.
1 Detergents are synthetic cleansing agents made Step 1 Preparation of lauryl hydrogen sulphate
from hydrocarbons obtained from petroleum
fractions. Thus, detergents are petrochemicals. CH3(CH2)10CH2O H + H2SO4 ⎯→
lauryl alcohol ( HO SO3H)
2 Detergents can be classified into three main types,
depending on the charge on the detergent ion. CH3(CH2)10CH2OSO3H + H2O
(a) Anionic detergents where the head of the lauryl hydrogen sulphate
detergent particle contains a negatively-
charged ion. Step 2 Preparation of sodium lauryl sulphate
CH3(CH2)10CH2OSO3 H + Na OH ⎯→
negatively- lauryl hydrogen sulphate
CH3(CH2)10CH2OSO3–Na+ + H2O
Example: R – O – SO3–Na+ charged ion sodium lauryl sulphate
(sodium alkyl sulphate)
(b) Cationic detergents where the head of the
detergent particle contains a positively-
charged ion.
Example: R – N(CH3)3+Br– positively-
charged ion
(c) Non-ionic detergents 5
Example: R– O– CH2CH2OH
Preparation of Detergent
1 The detergent, sodium alkyl sulphate can be Toothpaste
prepared from alcohols with chain lengths of The main ingredients in toothpaste are sodium
dodecyl sulphate (detergent), calcium carbonate or
12 to 18 carbon atoms in two steps. aluminium hydroxide (as abrasives to rub away the
Step 1 Reaction with concentrated sulphuric food and bacteria), glycerol (sweetener), cellulose
gum (thickener) and mint (for taste).
acid
The Structure of Detergent Molecule
O O
When a detergent is dissolved in water, it dissociates
to form sodium ions and detergent ions. The
R–O– H+H–O –S–O–H→ R–O–S–O–H detergent ions have the same basic structure as the
+ H2O soap ions, that is, it consists of two parts:
O O ( a) The ‘head’ is the sulphate group (–OSO3–)
long chain concentrated alkyl hydrogen which is negatively-charged and hydrophilic
(dissolves readily in water but not in oils and
alcohol sulphuric acid sulphate grease).
(b) The ‘tail’ is the long hydrocarbon chain, which
Step 2 Neutralisation with sodium hydroxide is neutral and hydrophobic (dissolves readily
solution in oils and grease but not in water).
O O alkyl sulphate ion
R – O – S – O – H + NaOH → R – O – S – O–Na+
+ H2O
O O
alkyl hydrogen sodium alkyl
sulphate sulphate
2 An example of a long chain alcohol is lauryl
alcohol (dodecan-1-ol), CH3(CH2)10CH2OH. The
deterg ent prepared from dodecan-1-ol is called
sodium dodecyl sulphate (IUPAC name) or
sodium lauryl sulphate (common name),
CH3(CH2)10CH2O-SO3–Na+.
503 Chemicals for Consumers
The Cleansing Action of Soap and Detergent
The cleansing action of soap or detergent depends on their chemical bonding and structures.
(a) The ionic ‘head’ (negatively-charged) is soluble in water (hydrophilic) but insoluble in
oil.
(b) The long hydrocarbon ‘tail’ (neutral) is insoluble in water (hydrophobic) but soluble in
oil.
The arrangement of soap or detergent Step 1 Action of soap on dirt
ions in the greasy layer
• When soap or detergent is mixed with water,
it lowers the surface tension of water and
wets the dirty surface.
• The negatively-charged ‘heads’ of soap
or detergent ions dissolve in water
(hydrophilic),
• The hydrocarbon ‘tails’ of soap or detergent
ions dissolve in the layer of grease
(hydrophobic).
5
Step 2 Dirt being surrounded by soap/
detergent ions
If the water is agitated slightly, the grease
begins to lift off the surface.
On agitation, grease begins to lift
off the surface
Greasy dirt particles are lifted from Step 3 Lifting dirt from cloth
the layer of cloth
On further agitation during washing, the
Emulsification of greasy dirt in greasy dirt is lifted from the surface since the
water as droplets density of grease is less than water.
Chemicals for Consumers Step 4 Emulsifying dirt in water
(a) When the water is shaken, the grease will
be emulsified when it breaks into smaller
droplets.
(b) These greasy droplets repel one another
because they carry the same charge. As
a result, the grease is suspended in the
solution.
(c) When the cloth is rinsed with water, the
droplets will be carried away.
504
• Soaps and detergents can act as emulsifying agents Part Y is soluble in water. 5
to emulsify oil and grease. The structural formula represents a soap ion (a
carboxylate). Since the formula contains 16 carbon
• The process of emulsification breaks large drops of atoms, it is called a palmitate.
grease into smaller droplets that float in water. Answer C
The cleaning process becomes more efficient if the Additives in Detergents
water containing the soap or detergent solution is
stirred vigorously or the washing is done at a higher 1 Modern detergents used for washing clothes
temperature. Heating and stirring help to loosen the usually contain a few types of additives to
dirt particles from the material being washed. (a) increase their cleaning power,
(b) make them attractive and saleable.
• When soap or detergent is added to clean water, the
‘head’ of the soap or detergent ion dissolves in water 2 Only about 20% of the substances in a detergent
while the ‘tail’ sticks out from the surface of water. are cleansing agents (sodium alkyl sulphate or
sodium alkylbenzene sulphonate). The other
substances are additives. The examples of
additives and their functions are described on
pages 508 to 509.
• Figure 5.4 shows the action of brighteners. The
brighteners absorb the invisible ultraviolet light and
reradiate it as blue light.
The ‘heads’ of the soap or detergent ions will weaken Figure 5.4 Action of brighteners
the forces of attraction between water molecules • Brighteners makes clothes appear whiter and brighter
because the blue light can hide any yellowing on the
and lower the surface tension of water. When the fabric.
surface tension is lowered, the water molecules will
spread out and wet the cloth or plates to be cleaned.
Hence, soaps act as wetting agents.
• The dirt particles surrounded by soap or detergent
ions are called micelles.
1 ’03 ’04
Part of the structural formula of a cleansing agent The Effectiveness of Soaps and SPM
is shown below. Detergents as Cleansing Agents
’11/P1
CH3(CH2)14COO–
X Y Advantages of Soaps SPM
Which of the following statements is true? ’11/P2
A Part X represents alkylbenzene. 1 Soaps are effective cleansing agents in soft
water, that is, water that does not contain
B Part Y is soluble in grease. Mg2+ and Ca2+ ions.
C The name of the structural formula is palmitate. 2 Soaps do not cause pollution problems to the
environm ent. This is because soaps are made
D The structural formula represents a detergent ion.
from chemicals found in animals and plants.
Comments This means that soaps are biodegradable.
Part X represents an alkyl group and not
alkylbenzene.
505 Chemicals for Consumers
Disadvantages of Soaps
1 Soaps are ineffective in hard water, that is, 2R – O – SO3–(aq) + Ca2+(aq) → (R – O – SO3)2Ca(aq)
alkyl sulphate ion calcium alkyl sulphate
water that contains magnesium and calcium
(detergent) (dissolves in water)
salts.
2 In hard water, soaps will react with Mg2+ and Hence, scum is not formed and the detergents
are still active in hard water and lathers
Ca2+ ions to form a precipitate called scum. easily.
Thus, soaps do not lather in hard water. 3 Detergents are synthetic cleansing agents. This
3 Scum is a grey solid that is insoluble in water. means that the structure of the hydrocarbon
chain can be modified to produce detergents
It consists of magnesium stearate and calcium with specific properties. Nowadays, different
types of detergents have been synthesised
stearate. for specific uses such as shampoos and dish
cleaners.
Mg2+(aq) + 2C17H35COO–(aq) → (C17H35COO)2Mg(s) 4 Furthermore, detergents are also effective in
stearate ion magnesium stearate acidic water because H+ ions in acidic water
do not combine with detergent ions.
(soap ion) (scum)
Ca2+(aq) + 2C17H35COO–(aq) → (C17H35COO)2Ca(s)
stearate ion calcium stearate
(soap ion) (scum)
5 4 Soaps are also not effective in acidic water, Disadvantages of Detergents
for example, rainwater containing dissolved
acids. H+ ions from acids will react with soap 1 Most detergents have branched hydrocarbon
ions to produce fatty acid molecules of large chains and are non-biodegradable. As a
molecular size that are insoluble in water. result, non-biodegradable detergents cause
water pollution.
C17H35COO–(aq) + H+(aq) → C17H35COOH(s)
stearate ion stearic acid 2 Phosphates in detergents act as fertilisers and
promotes the growth of water plants and
(soap ion) algae. When the plants die and decay, they
use up the oxygen dissolved in water. This will
5 Stearic acids and other fatty acids do not decrease the oxygen content in water and kill
act as cleansing agents because they exist fishes and other aquatic organisms.
mainly as molecules and do not have anionic
hydrophilic ends (‘heads’) that dissolve in 3 Detergents produce a lot of foam in water. The
water. layer of foam that covers the water surface will
prevent oxygen from dissolving in water. This
Advantages of Detergents condition will cause fish and other aquatic
life to die from oxygen starvation.
1 Detergents are cleansing agents that are
effective in soft water as well as hard water. 4 Additives such as sodium hypochlorite
This is because detergents do not form scum (bleaching agent) releases chlorine gas in
with Mg2+ ions and Ca2+ ions found in hard water that is acidic. Chlorine gas is highly
water. toxic and kills aquatic life.
2 The detergent ions (R – O – SO3–) react with The cleansing agents for window glass or mirrors are
Mg2+ and Ca2+ ions in hard water. However, volatile liquids. The chemicals usually used in the
the magnesium salts and calcium salts which cleansing agents are isopropyl alcohol (propan-2-ol).
are formed are soluble in water. Ammonia is added to enhance the cleansing power.
2R – O – SO3–(aq) + Mg2+(aq) → (R – O – SO3)2Mg(aq)
alkyl sulphate ion magnesium alkyl sulphate
(detergent) (dissolves in water)
Chemicals for Consumers 506
2 ’06
The following chemical equations show the reactions C The concentration of stearate ions decreases.
between alkyl sulphate ions, ROSO3– and stearate D The concentration of stearate ions remains
ions, CH3(CH2)16COO– with magnesium ions, Mg2+ in
hard water. R represents long hydrocarbon chain. unchanged.
2ROSO3–(aq) + Mg2+(aq) → (ROSO3)2Mg(aq) Comments
The equation shows that alkyl sulphate ions do not
2CH3(CH2)16COO–(aq) + Mg2+(aq) → form a precipitate with Mg2+ ions but stearate ions form
(CH3(CH2)16COO)2Mg(s) a precipitate with Mg2+ ions. As CH3(CH2)16COO–
What is the effect of adding magnesium ions to a (aq) reacts with Mg2+(aq) to form a precipitate
solution containing alkyl sulphate ions or stearate of (CH3(CH2)16COO)2Mg, the concentration of
ions? CH3(CH2)16COO–(aq) decreases.
Answer C
A The concentration of alkyl sulphate ions decreases.
B The concentration of alkyl sulphate ions increases.
5
Cleansing agents
Soaps Detergents
• Detergents are synthetic cleansing
• Soaps are cleansing agents made from
animal fats or vegetable oils. agents made from petroleum products.
History of soap making Preparation of soap by Preparation of detergent from
• In ancient times, soaps were saponification petroleum fractions
made from ashes and soda. Fats or oils + NaOH(aq) • Sodium alkyl sulphate
• Ernest Solvay and Michel → soap + glycerol
∆ ROSO3H + NaOH(aq) → ROSO3Na + H2O
Chevreul are the chemists that
contributed to the development Soap is RCOONa (R is a
of the soap industry in the past. long hydrocarbon chain)
Effectiveness of the cleansing Cleansing action of soaps and detergents
action of soaps and detergents • The ‘head’ dissolves in water.
• Soaps are ineffective in hard
water or acidic water because of –COO– (in soaps) and OSO3– (in detergents)
the formation of precipitates that
are insoluble in water. • The ‘tail’ (long hydrocarbon chain) dissolves in oil.
• Soaps react with Mg2+ and Ca2+ • Agitation of water causes grease to lift off the surface.
in hard water to form scum.
• Detergents are effective in both Additives in detergents
hard water and acidic water
because no scum is formed. • Builders: soften water
• Detergents cause water pollution.
• Whitening agents: remove coloured stains
• Biological enzymes: remove protein stains
• Brighteners: make clothes look brighter and whiter
• Drying agent: to keep the detergent dry
• Perfume: to make clothes smell fresh
• Stabilisers • Antiseptics
507 Chemicals for Consumers
55
Chemicals for Consumers 508
55
509 Chemicals for Consumers
3 ’07
(a) Name the type of reaction that has occured in the Solution
following reaction. (a) Saponification (alkaline hydrolysis)
(b) Glycerol
Vegetable oil + NaOH → soap + compound X (c) Soap is precipitated out.
(b) State the name of compound X.
(c) What happens when sodium chloride is added to
the soap mixture?
5.1 3 Complete the flowchart to compare the advantages
and disadvantages of soap and detergent.
1 (a) What is meant by soap?
(b) State the raw materials needed in the preparation Soap
5 of soap.
(c) A naturally occurring ester has the structural
Advantages Disadvantage
formula as shown below. (a)
O (b)
CH2 – O – C – C17H35
O Detergent
CH – O – C – C15H31 Advantages Disadvantages
O (a)
CH2 – O – C – C17H35 (b)
Write an equation to show the reactions involved
when soap is prepared from this ester.
2 Sodium alkyl sulphate acts as a detergent and has
the formula shown below.
C12H25 – O – SO3–Na+
(a) State the characteristics of sodium alkyl sulphate
that enable it to act as a detergent.
(b) Using sodium alkyl sulphate as an example,
describe the action of detergents on the greasy
stains found on a piece of cloth.
5.2 Uses of Food Additives (a) making food last longer by preventing the
growth of microorganism,
Types of Additives and Examples
(b) making food last longer by preventing the
1 Food preservatives have been used since
ancient times. Ancient civilisation used salt oxidation of fats and oils by oxygen in air,
to preserve meat and fish, herbs and spices to
improve the flavour of food. (c) making food taste or smell better,
(d) improving the texture of food and to
2 Food additives are chemicals that are added to
food in small quantities for specific purposes prevent food from becoming liquid,
such as
(e) restoring the colour of food destroyed
during food processing, and
(f) adding colouring to food so as to make
the food look fresher, more interesting or
more appetising.
Chemicals for Consumers 510
3 There are six types of food additives as shown
below.
Preservatives Antioxidants Drying fruits and meat is one of the oldest methods of
food preservation. Drying is effective because water is
Stabilisers Type Thickeners necessary for the growth of microorganisms.
of food
additives Salt and sugar can also be used for food preservation
because the dissolved salt and sugar will cause water
Flavouring agents Dyes to flow by osmosis from the microorganisms to its
surroundings. The dehydration process stops the growth
of microorganisms.
Functions of Food Additives SPM
’09/P1, ’10/P2, ’11/P1, P2
Preservatives
1 Preservatives are chemicals that are added to food to retard or to prevent the growth of microorganisms 5
such as bacteria, mould or fungus so that the food can be stored for a longer period.
2 In ancient times, food additives from natural sources such as salt, sugar and vinegar were used to
preserve food and to make the food taste better.
3 Nowadays, synthetic preservatives are used. Table 5.2 shows the types of preservatives commonly
used. Many of the preservatives are organic acids and salts of organic acids.
Table 5.2 Types of preservatives and their uses
Preservative Molecular formula Uses
Sodium nitrite NaNO2 • To preserve meat, sausage, cheese and dried fish
Sodium nitrate NaNO3 • To prevent food poisoning in canned foods
• To maintain the natural colour of meat and to make
them look fresh
Benzoic acid C6H5COOH • To preserve sauces (oyster, tomato or chili), fruit juice,
Sodium benzoate C6H5COONa jam and margarine
SO2
Sulphur dioxide Na2SO3 • Used as bleaches and antioxidants to prevent browning
Sodium sulphite in fruit juices
• Maintain the colour and freshness of vegetables
• To prevent the growth of microorganisms
Antioxidants
1 Antioxidants are chemicals that are added to foul odours (for example, butanoic acid,
food to prevent the oxidation of fats and oils 3 ACn3Hti7oCxOidOanHts).are added to fats, oils, cakes,
by oxygen in the air.
sausages, biscuits and fried food to slow
2 Food containing fats or oils are oxidised and down the oxidation process.
become rancid when exposed to air. This makes 4 Ascorbic acid, citric acid and sodium citrate
the food unfit for consumption. The rancid are examples of antioxidants.
products are volatile organic compounds with
511 Chemicals for Consumers
Flavouring Agents
1 There are two types of flavouring agents: in food and drink. However, the use of
artificial flavours and flavour enhancers. They saccharin is banned in many countries
because it is a suspected carcinogen.
are added to food to make them taste better. 5 Many esters have fruity odours and tastes
2 Flavour enhancers have little or no taste of and are used as artificial flavours. Table 5.3
shows some examples of esters that are used
their own. They are chemicals that are added in making drinks.
to food to bring out the flavours or to enhance Table 5.3 Uses of esters as flavouring agents
the tastes of food. An example of a flavour Ester Benzyl Octyl Ethyl
enhancer is monosodium glutamate (MSG).
3 Artificial flavours include sweeteners and ethanoate ethanoate butanoate
other flavours such as peppermint or vanilla.
Aspartame and saccharin are examples of Flavour Strawberry Orange Pineapple
artificial sweeteners.
4 Both aspartame and saccharin can be used as
a substitute for sugar to enhance the sweetness
Stabilisers and Thickening Agents
5 1 Stabilisers and thickening agents improve the of chocolate milk, oil and vinegar in salad
texture and the blending of food. dressing will separate as soon as mixing is
stopped.
2 Stabilisers are chemicals that are used to enable oil 5 Thickening agents are chemicals that are
and water in the food to mix together properly in added to food to thicken the liquid and to
order to form an emulsion. Examples of stabilisers prevent the food from liquefying. Thickening
are gelatin, acacia gum, lecithin and pectin. agents (also called thickeners) absorb water
and thicken the liquid in food to produce a
3 Stabilisers are added to improve the texture of jelly-like structure.
food. For example, stabilisers are added to ice 6 Most thickening agents are natural
cream and peanut butter to keep them smooth carbohydrates. Gelatin and pectin are added
and creamy. to help jams and jellies set.
4 Without stabilisers, ice crystals would form in
ice cream, particles of chocolate would settle out
Dyes
1 Dyes (colouring agents) are chemicals that are added to food to • Pectin, gelatin and acasia gum
can be used as both stabilisers
give them colour so as to improve their appearance. and thickeners.
2 Some food are naturally coloured, but the colour is lost during
• Some food are hygroscopic,
food processing. The food industry uses synthetic food colours to that is, they absorb moisture
from the air and become lumpy.
(a) restore the colour of food lost during food processing, Anticaking agents such as
calcium silicate and magnesium
(b) enhance natural colours, so as to increase the attractiveness silicate are added to table salt
and baking powder to keep them
of food, dry.
(c) give colour to food that do not have colour. • Other food additives include
3 Some dyes are natural plant pigments while others are synthetically – acidity regulators (to control
prepared. The synthetic colours used in food are azo and triphenyl pH of food)
compounds. Both these compounds are organic compounds. – antifoaming agents
4 The synthetic dye, brilliant blue, is an example of triphenyl – bulking agents (like starch to
increase food bulk)
compound. The synthetic dye, tartrazine and sunset yellow are – humectants (prevent food
from drying out)
examples of azo compounds.
5 Azo compounds are organic compounds containing the diazo
group, – N = N –, and are usually yellow, red, brown or black in
colour. Triphenyl compounds are organic compounds containing
three phenyl groups, –C6H5, and are usually green, blue or purple
in colour.
Chemicals for Consumers 512
Naturally occurring colouring agents can be extracted Brain damage
from the flowers, leaves or roots of plants.
For example, beta-carotene, the orange-red substance Excessive intake of nitrites for a prolonged
in carrots and a variety of plants is an example of period of time can cause brain damage. In this
natural food colour. Beta-carotene is added to butter condition, the supply of oxygen to the brain is
and margarine. disrupted and this causes brain damage.
Effects of Food Additives on Health SPM Hyperactivity
’10/P2 1 Food additives such as tartrazine can cause
hyperactivity.
1 The types of food additives allowed and the
quantity permitted are controlled by the 1983 2 Children who are hyperactive become very
Food Act and the 1985 Food Regulation. active, find it difficult to relax or sleep and
are very restless.
2 The permissible quantity depends on the type
of food and the food additives. For example, Reading the Food Label
benzoic acid added must not exceed 800 mg
per kg in cordial drinks, whereas sodium 1 You must read the label on the food package 5
nitrite must not exceed 100 mg per kg in meat to identify
products. (a) brand name,
(b) the net weight,
3 The excessive intake of food additives for a (c) the halal symbol for Muslim consumers,
prolonged period of time will ruin our health. (d) the nutrient content (for example, carbohy
The side effects arising from taking food drates, proteins and fats, minerals and
additives are allergy, cancer, brain damage and vitamins),
hyperactivity. (e) food additives used,
(f) expiry date,
Allergy (g) address of the manufacturer.
1 Food additives such as sodium sulphite 2 Food additives listed in the food labels are
(preservative), BHA and BHT (antioxidants), usually represented by the code number
MSG (flavouring) and some food colours – E. This code number shows that the food
(e.g. Yellow No. 5) can cause allergic reactions additives have been approved.
in some people.
3 Figure 5.5 shows a typical food label for an
2 The symptoms of MSG allergy are giddiness, orange drink.
chest pain and difficulty in breathing. This
condition is called the ‘Chinese restaurant ascorbic sodium expiry
syndrome’. acid benzoate date
3 The presence of sodium nitrate or sodium XYZ Orange drink
nitrite in food can cause ‘blue baby’ syndrome
that is fatal for babies. This syndrome is due Ingredients: Water, sugar, Use before
to the lack of oxygen in the blood. Hence,
the use of nitrate and nitrite is not allowed
in baby food.
citric acid, E330 31-1-2009
Cancer Stabilisers: E466, preservative E211
1 Chemicals that cause cancer are called Sweetener: aspartame
carcinogens. Sodium nitrite (a preservative)
is a potent carcinogen. Colouring agents: E110, E102, vitamins A and D
2 The nitrite reacts with the amines in food yellow-orange tartrazine
to produce nitrosamine which can cause
cancer. (dye) (dye)
Figure 5.5 A typical food label
513 Chemicals for Consumers
5 The Rationale for Using Food Additives Disadvantages
Advantages 1 Eating food additives such as preservatives,
antioxidants and flavour enhancers in excess
1 To prevent food spoilage quantities over a long period of time is
(a) Oxidation and microorganisms (bacteria, detrimental to health. These additives have
fungi) are the main causes in the little nutritional value.
decomposition of food. In a hot climate, meat
and fish rot easily. The use of preservatives is 2 Some of the synthetic food additives can cause
an effective way to prevent food spoilage. allergy, cancer and hyperactivity.
(b) If preservatives are not used, food spoilage
might drastically reduce the food supply, Life Without Food Additives
making for costlier food.
(c) Few deaths are associated with the use Imagine life without food additives. The following
of food additives. However, many people situations will occur.
have died due to food poisoning caused 1 Food spoilage will drastically reduce the food
by bacterial toxins.
supply. This will result in food shortages
2 For medical reasons around the world.
(a) Aspartame and sorbitol are used to make 2 Diseases will flourish again due to deficiencies
food and drink sweet without using sugar. of vitamins and minerals in our food.
These food additives are particularly useful as 3 Loss of appetite will be common particularly
artificial sweeteners for diabetic patients. among the younger generation because our
(b) Artificial sweeteners give the sweet taste food will not look, taste and smell good and
but without adding calories to the food. this will affect their appetites.
Thus, they can be used to reduce obesity.
Uses of food additives
• To make food last longer (to extend the shelf life)
• To make food taste better and look better
Types of food additives Functions of food additives Effects on health
• Preservatives: sodium nitrite, • Preservative: to inhibit or prevent • Allergy: MSG
• Carcinogenic: NaNO2
sodium benzoate the growth of moulds, yeasts and • Brain damage
• Antioxidant: ascorbic acid bacteria that spoil food • Hyperactivity
• Flavouring: MSG, aspartame • Antioxidants: to prevent spoilage
• Stabiliser and thickener: gelatin of food due to oxidation by
oxygen
and acacia gum • Flavouring agents: to enhance the
• Dye: azo compounds, triphenyl taste of food
• Stabilisers and thickeners: to
compounds improve the texture of food
• Colouring agents: to restore the
Chemicals for Consumers colour or to enhance the natural
colour of food
514
5.2 2 Traditional medicine are medicine derived 5
from natural sources such as plants and animals
1 (a) What is meant by food additives? without being processed chemically.
(b) State two methods of food preservation which
The source and uses of some animals and animal
’03 are used in our daily lives. Explain how these parts as medicine are shown below.
methods work. • Sea horses – For treating respiratory disorders such
2 State the function and application of as asthma and skin ailments
(a) acacia gum, • Soft-shelled turtles – Improve blood circulation
(b) aspartame in the food industry. • Tiger bones – For curing joint pain and stiffness, back
3 Explain the advantages and disadvantages of using pain and rheumatism
artificial colourings as food additives. • Bear bile (from bear gall bladder) – To treat illnesses
5.3 Medicine ranging from liver cancer to haemorrhoids (common
name: piles) to conjunctivitis
Sources and Uses of Traditional The use of animals or animal parts as medicine should
Medicine be banned. This is because killing animals or removing
animal parts is a cruel act. Furthermore, many of these
1 Medicine is a substance used to prevent or cure animals are endangered and should be protected.
diseases or to reduce pain and suffering due
to illnesses. 3 Medicine obtained from plants are known
as herbal medicine. The sources and uses of
some herbal medicine are shown in Table 5.4.
Table 5.4 Some examples of herbal medicine
SPM Plant Part of the plant used Uses
’06/P2
Garlic Corm • For preventing flu or asthma attacks
• For reducing high blood pressure
Ginger Rhizome (horizontal • For treating stomach pain due to wind in the
underground stem) stomach
• For supplying heat energy to keep the body
warm
• For preventing flu attack
Aloe vera Leaves • For treating itchy skin
Lemon (lime) • For treating burns (scalding) on the skin
Quinine
Ginseng Fruits • For treating boils or abscesses on the skin
• For preventing flu attack
Lemon grass • For treating skin diseases
Tongkat ali
Bark of Cinchona tree • For treating malaria
• For preventing muscle cramps
Roots • As a tonic to improve the overall health of
human beings
• For increasing energy, endurance and reducing
fatigue
Stem/leaves • Has antibacterial and antifungal properties
• For treating coughs
Roots • As a tonic for after birth and general health
515 Chemicals for Consumers
Modern Medicine
1 Modern medicine can be classified as follows Modern drugs have a trade name and a generic
based on their effects on the human body: name. For example, the analgesic aspirin (generic name)
(a) Analgesics
(b) Antibiotics is sold under different brand names such as Caprin
(c) Psychotherapeutic drugs and Disprin. Similarly, paracetamol (generic name) is
sold under the trade name of Panadol.
2 Some examples of modern medicine are
shown in Table 5.5. Function of Each Type of Modern Drugs SPM
Table 5.5 Examples of modern drugs ’04/P1
’04/P2
’05/P1
Type of modern drug Example Analgesics
(a) Analgesics Aspirin, paracetamol, 1 Analgesics are medicine that relieve pain.
codeine Examples of analgesics are aspirin, paracetamol
and codeine. Analgesics are sometimes called
(b) Antibiotics Penicillin, painkillers.
streptomycin
2 Aspirin and paracetamol are mild painkillers
(c) Psychotherapeutic Stimulant, whereas codeine is a powerful painkiller.
drugs antidepressant 3 Analgesics relieve pain but do not cure the
disease. Table 5.6 shows the chemical aspect
5 and antipsychotic and functions of some analgesics.
Table 5.6 Types of analgesics and their functions
Type of analgesic Chemical aspect Function
Aspirin IUPAC name: Acetyl salicylic acid • Relief pain and has anti-inflammatory
Functional groups: a carboxylic acid action
group and an ester group
• Used to
COOH carboxylic group – reduce fever
– relieve headaches, muscle aches and
O joint aches
– treat arthritis, a disease caused by
inflammation of the joints
– act as an anticoagulant. It prevents
O – C – CH3 the clotting of blood and reduce the
risk of heart attacks and strokes
ester group
Thus, aspirin is acidic in nature
Paracetamol Structural formula: • Similar to aspirin in its effects but it
does not reduce inflammation
SPM H O
• Reduces or relieves flu symptoms such
’07/P1, | as fever, bone aches and runny nose
’09/P1
HO – – N – C – CH3
Thus, unlike aspirin, paracetamol is
neutral in nature
Codeine Codeine is an organic compound that • Used to relieve minor to moderate
contains the elements carbon, hydrogen, pain. It is more powerful than aspirin
oxygen and nitrogen and paracetamol but less powerful than
morphine. Codeine and morphine are
narcotic drugs
• Also used in cough mixtures for
suppressing coughs
Chemicals for Consumers 516
Antibiotics: Antibacterial Medicine (c) Penicillin is only effective on certain
bacteria. For example, it cannot be used to
1 Antibiotics are chemicals that destroy or prevent treat tuberculosis.
the growth of infectious microorganisms.
5 Streptomycin is the antibiotic that is effective
2 Two examples of antibiotics are penicillin and in treating tuberculosis.
streptomycin.
Psychotherapeutic Medicine
3 Antibiotics are used to treat diseases caused by
bacteria and are not effective against diseases 1 Psychotherapeutic medicine are a group of
caused by viral infections such as influenza, drugs that change the emotions and behaviour
measles or small pox. of the patient and are used for treating mental
or emotional illnesses.
4 Penicillin
(a) Penicillin is derived from the mould 2 Table 5.7 shows the types and functions of
Penicillium chrysogenum. psychotherapeutic drugs.
(b) Penicillin is used to treat diseases, caused by
bacteria, such as pneumonia, gonorrhoea
and syphilis.
Table 5.7 Types and functions of psychotherapeutic drugs
Type of Functions Examples Comments 5
psychotherapeutic drug
Stimulants • To maintain or Caffeine • It is found in coffee, tea
These are drugs that increase alertness Amphetamine and Cola drinks
stimulate (excite) the
activity of the brain • To counteract normal • It is a weak, naturally
and the central nervous fatigue occurring stimulant
system
• To elevate mood • A strong synthetic
stimulant
• It increases the heart and
respiration rates as well as
blood pressure
Antidepressants • To alleviate depression • Tranquiliser • They are substances
These are drugs that • To relieve anxiety or • Barbiturate that depress the central
increase the brain’s level nervous system and cause
of neurotransmitters and tension drowsiness
thus improve mood • To make a person feel
calm and sleepy
Antipsychotic medicine • To treat mental illness • Lithium carbonate • Mental (psychotic)
such as schizophrenia • (CLhi2loCrOop3)romazine patients have extreme
(madness) • Haloperidol mood swings. Their mood
changes rapidly from high
spirits to deep depression
• Antipsychotic medicine
do not cure mental illness
but it can reduce some of
the symptoms to help the
person live a more normal
life
517 Chemicals for Consumers
4 ’07 Side Effects of Traditional Medicine
Which of the following can relieve joint and 1 It is generally believed that traditional medicine
have little side effects compared to modern
muscle aches? medicine.
I Paracetamol 2 However, taking high doses of quinine for
a prolonged period may cause hearing loss.
II Barbiturate German health officials reported 40 cases of
liver damage which were linked to the herbal
III Aspirin medicine containing kava-kava.
IV Streptomycin 3 While the use of traditional medicine is rising
globally, health experts have insufficient data
A I and II only C II and IV only about how it affects patients.
B I and III only D III and IV only 4 The World Health Organisation (WHO) hopes
to set up a global monitoring system to monitor
Comments the adverse side effects of traditional medicine.
Analgesics such as aspirin, paracetamol and
codeine are used to relieved pain.
Answer B
Side Effects of Modern Medicine
5 1 Table 5.8 shows the side effects of modern medicine.
Table 5.8 Side effects of modern medicine
Type of modern drug Side effects
Aspirin
Amphetamine • Can cause bleeding in the stomach because aspirin is very acidic
• Can cause allergic reactions, skin rashes and asthmatic attacks
Codeine
Penicillin • People who abuse amphetamines are excitable and talkative
Streptomycin • Psychologically addictive and can cause heart attack
Stimulant • Can cause anxiety, sleeplessness, aggressive behaviour and decrease appetite
Antidepressant • Can cause enlarged pupils, heavy perspiration and trembling hands
Antipsychotic drug
• Can cause addiction
• Can cause allergic reactions
• Can cause death to people who are allergic to it
• Can cause nausea, vomiting, dizziness, rashes and fever
• Can cause loss of hearing following long-term use
• Can cause addiction
• Can cause addiction
• Can cause headaches, grogginess and loss of appetite
• Can cause dry mouth, blurred vision, urinary retention, constipation
• Can cause tremor and restlessness
• Sedation (make people calmer or make people sleepy)
2 Correct ways of using medicine Discuss with your doctor and listen to him
In taking any medicine, we should know why
the medicine is prescribed, how the medicine concerning the medicine to be taken.
should be used, what special precautions should (b) Follow the instructions given
be followed, what special diet should be
followed, what are the side effects and what Follow the instructions given by your doctor
storage conditions are needed. In addition, we or pharmacist concerning the dosage and
should note the following points: method of taking the medicine.
(a) Self-medication Dosage: Never take larger or more frequent
Do not prescribe medicine for yourself doses and do not take the drug for longer
(self-medication) or for other people.
than directed.
Method of taking: Different drugs are taken
in different ways. For example, medicine
Chemicals for Consumers 518
that are acidic (such as aspirin) must be 5.3
taken after food. If taken on an empty
stomach, the medicine will damage the 1 (a) State the difference in the effect of using
stomach lining. Conversely, antacid tablets aspirin and paracetamol as medicine.
are usually taken before food.
(c) Medicine for adults and children (b) Give a simple chemical test that can be used
Medicine for adults should not be given to distinguish aspirin from paracetamol.
to children and vice versa.
(d) Use of antibiotics 2 State two similarities and one difference between
Complete the whole course of antibiotic penicillin and streptomycin.
treatment given by your doctor. Do not
stop taking the antibiotic just because you are 3 State
already feeling well. If not, the remaining (a) the use of aspirin,
bacteria will mutate and develop resistance (b) the side effects of aspirin.
to the antibiotic and render it ineffective
in the future. Traditional medicine
(e) Side effects • Derived from plants and animals
Visit the doctor immediately if there are
symptoms of allergy or other side effects • Types and functions 5
of the drugs. of medicine
(f) Expiry date Medicine
Like food, medicine also have expiry dates. • Side effects of modern
Do not take medicine after their expiry and traditional
dates. medicines
• Correct usage of
modern and traditional
medicines
Addiction to certain medicine causes psychological Modern medicine
dependence, physical dependence and tolerance.
• Psychological dependence: an uncontrollable desire Analgesics Antibiotics Psychotherapeutic
• Aspirin • Penicillin drugs
for the medicine. • Paracetamol • Streptomycin
• Physical dependence: acute withdrawal symptoms • Codeine • Stimulants
• Antidepressants
such as convulsions. • Antipsychotics
• Tolerance for the medicine is shown by the increasing
5.4 Appreciating the
dosage required to produce the same effect. Existence of Chemicals
5 ’05 1 Since the last 100 years, thousands of new
chemicals are synthesised. These new chemicals
Which of the following statements about aspirin include synthetic polymers, composite materials,
are correct? antibiotics, detergents and modern medicine.
I It is an analgesic. These chemicals improve the quality of life.
II It destroys bacteria.
III It can relieve headache. 2 Modern chemical substances have brought
IV It calms down the emotions of the patient. enormous benefits to mankind. However,
the chemicals have side effects on life and
A I and III only C I, II and III only
B II and IV only D II, III and IV only
Comments
Aspirin is an analgesic and is used to relieve pain.
Answer A
519 Chemicals for Consumers
the environment. We must practise proper In recent years, food irradiation is used in food
management of chemicals towards a better preservation. It is well known that gamma rays can kill
life, hygiene and health. insects, parasitic worms (such as trichinae in pork) and
3 Modern living depends on chemical substances. bacteria such as Salmonella sp. and E. coli (in beef) .
Try to imagine the world without chemicals.
For example, without petroleum, the transport In food irradiation, the food is exposed to high-
system will break down; without modern energy gamma radiation. Irradiation can extend the
medicine, diseases will spread and without soap shelf lives of food for weeks or even months.
and detergent, the world will become more
dirty and less hygienic.
1 Soaps are the sodium or potassium salts of long 11 Food additives that are commonly used are
chain fatty acids.
preservatives, antioxidants, flavouring agents, stabilisers,
2 Detergents are the sodium salts of alkyl hydrogen
sulphate. thickening agents and dyes.
5 3 Soap is prepared by the saponification (alkaline 12 Preservatives (sodium nitrite and sodium benzoate)
hydrolysis) of vegetable oils or animal fats.
are used to retard the growth of bacteria, mould or
Vegetable oil + NaOH(aq) ⎯bo→il glycerol + soap
fungus.
4 The structure of a soap ion or a detergent ion consists
of a hydrophobic part and a hydrophilic part. The 13 Antioxidants (ascorbic acid and sodium citrate) are
hydrophobic part is the long chain hydrocarbon
which is soluble in grease but insoluble in water. used to prevent the oxidation of fats and oils by air.
5 For a soap ion, the hydrophilic part is –COO–. For 14 Flavouring agents such as monosodium glutamate
the detergent ion, the hydrophilic part is –OSO3–.
The hydrophilic part is negatively-charged and is (MSG) enhance the taste of food.
soluble in water but insoluble in grease.
15 Stabilisers and thickening agents (gelatin and
6 The following additives are added to detergents to
increase their cleaning power. acacia gum) improve the texture and the blending
• Builders
• Whitening agents of food.
• Biological enzymes
• Brighteners 16 Dyes (azo compound and triphenyl compound) are
7 Builders – to remove Mg2+ and Ca2+ ions in hard colouring agents added to food to give them colour
water
so as to improve their appearance.
Whitening agents – to remove coloured stains
Biological enzymes – to remove protein stains 17 Traditional medicine are medicine derived from
Brighteners – make fabrics appear whiter and
natural sources such as plants and animals without
brighter
8 Soaps do not cause water pollution because they being processed chemically.
are biodegradable. However, they are not suitable 18 Garlic is used for reducing high blood pressure and
for use in hard water (or acidic water) because they
form scum and their cleansing action is reduced. ginger is used to remove wind in the stomach.
9 Detergents cause water pollution because they are
non-biodegradable. However, they are suitable for 19 Modern medicine can be classified as follows:
use in hard water (or acidic water) because they do
not form scum. • Analgesics • Psychotherapeutic drugs
10 Food additives are chemicals that are added to
food in small quantities for specific purposes. • Antibiotics
20 Analgesics are used to relief pain. Examples of
analgesics are aspirin, paracetamol and codeine.
21 Antibiotics are used to treat diseases caused by
bacteria. Examples of antibiotics are penicillin and
streptomycin.
22 Psychotherapeutic medicine are drugs used for
treating mental or emotional illness.
23 Examples of psychotherapeutic medicine:
• Stimulants (for example, amphetamine)
• Antidepressants (for example, barbiturate)
• Antipsychotic medicine – to treat mental illness
24 Most medicine have side effects. For example,
• aspirin can cause bleeding in the stomach,
• amphetamine, codeine, stimulants and antide
pressants can cause addiction.
Chemicals for Consumers 520
5
Multiple-choice Questions
5.1 Soaps and Detergents Which statement about the ’03
1 Which of the following is produced reaction is correct? Which of the following
when a mixture of palm oil and A It is a saponification reaction. statements about the carbon
concentrated sodium hydroxide B It is an esterification reaction. compound is true?
solution (in excess) is boiled? C It is used to make detergent. A It is a detergent ion.
A Fatty acids only D The product glycerol is a B Part X and part Y are both
B Salt of the fatty acids only
C A mixture of glycerol and cleaning agent. soluble in water.
fatty acids C Part X and part Y are both
D A mixture of glycerol and salt 6 Which of the following ions
of the fatty acids soluble in grease.
reacts with soap solution to D Part X is soluble in grease
form scum? and part Y is soluble in water.
A Na+ C Cl– 12 Soaps and detergents
A are salts of fatty acids.
B Ca2+ D SO42– B contain the same functional
group.
2 Which of the following is an ester? 7 Which of the following C form scum with strongly 5
A Palm oil chemicals is not needed in the acidic solution.
B Soap D contain the hydrophobic part
C Sodium palmitate preparation of the detergent, that is soluble in oil and grease.
D Glycerol
sodium alkyl sulphate? 13 Which of the following statements
3 Which of the following is A Sodium hydroxide are true regarding soaps?
correctly matched with the B Concentrated sulphuric acid
manufacturing process? C Alkylbenzene sulphonic acid I Soaps are biodegradable.
D Alcohol with large molecular II Soaps lather readily in hard
size water.
III Soaps are ineffective in acidic
Chemical Manufacturing 8 Which of the following statements
process about detergent is true? water.
A Detergents are covalent IV Soaps are prepared from
A Soap Neutralisation of
vegetable oils compounds. sulphonic acid.
B Detergents are made from A I and III only
B Soap Alkaline B II and IV only
hydrolysis of petroleum. C I, III and IV only
vegetable oils C Detergents contain the D I, II, III, and IV
C Detergent Neutralisation –COO– group in its molecules. 14 A sodium compound has the
of long chain D Detergents are less effective following formula:
alcohol
than soap in hard water. ’08 O
D Margarine Oxidation of 9 The hydrophilic group in the
unsaturated fats detergent, sodium dodecyl R – O – S – O–Na+
(lauryl) sulphate is
4 In the soap industry, sodium ABC –––OOCOSSOOO43–2–– O
chloride is used to D CH3(CH2)10CH2–
A prevent the formation of scum. R is a long hydrocarbon
B decrease the surface tension 10 Which of the following substances chain. Which of the following
of water. acts as a whitening agent? statements are true regarding
C produce a softer soap. A Sodium borate this compound?
D decrease the solubility of B Sodium perborate I The compound is used as a
soap in soap solution. C Sodium tripolyphosphate
D Biological enzyme detergent.
5 The following equation shows a
chemical equation. 11 The diagram shows the structure
of a carbon compound.
’09 Fat + NaOH →
Glycerol + sodium salt
521 Chemicals for Consumers
II The molecule has a part that 19 Which of the following is true 5.3 Medicine
is insoluble in water. about soap or detergent? 24 A student has a headache.
’06 A Soap forms scum in soft water.
III The compound is an example Which of the following medicine
B Detergent forms scum in ’05 will relieve his headache?
of sodium alkyl sulphate.
hard water. A Streptomycin C Aspirin
IV The compound can break large C Scum decreases the B Amphetamine D Insulin
droplets of grease into smaller effectiveness of soap as a 25 Which of the following modern
medicine is matched correctly
droplets of grease. cleansing agent.
A I and III only D The presence of sulphate ’09 with its function?
B II and IV only
C I, II and III only ion in detergent forms
D I, II, III and IV
scum.
15 Amylase and lipase are additives Medicine Function
added to detergent. 5.2 Uses of Food Additives A Aspirin Antibiotic
B Insulin Antibiotic
What is the function of these 20 Which of the following are the C Paracetamol Analgesic
functions of food additives? D Streptomycin Analgesic
additives?
A They act as drying agents. ’09 I To enhance the flavour of food 26 Which of the following belongs
B They act as bleaching agents II To increase the rate of
C They remove protein stains. to the class of medicine called
D They make clothes look metabolism
III To decrease the rate of psychotherapeutic drugs?
brighter.
oxidation of food
5 16 Which of the following molecules IV To make food more digestible A Codeine C Penicillin
act as cleansing agents? A I and II only B Aspirin D Stimulant
B I and III only
I CH3(CH2)3COONa C II and IV only 27 A patient is experiencing
IIVIIAII CCCIHHHa333n(((dCCCHHHII222o)))111n566lCCOyOH SO3O3NNaa D I, III and IV only
depression and has difficulty in
21 Which of the following food
sleeping. Which of the following
B III and IV only additives is used to stop the
medicine is suitable for treating
C II, III and IV only activity of microorganisms in
this patient?
D I, II, III and IV food? A Barbiturate
A Ascorbic acid B Codeine
17 A section of the anion of a B Benzoic acid C Lithium carbonate
cleaning agent is shown below. C Citric acid D Paracetamol
D Triphenyl compounds
’04 CH3(CH2)14COO– 28 Which of the following medicine
22 Which of the following food
Which of the following is true have antibacterial properties?
about the ion? additives is used to improve the
A It is glycerol. I Barbiturate
B It is a detergent ion. texture of ice cream?
C It is palmitate ion. A Pectin II Penicillin
D It is stearate ion. B Citric acid
C Sodium nitrate III Paracetamol
D Aspartame
IV Streptomycin
A I and III only
B II and IV only
C III and IV only
D I, II and III only
18 When a concentrated sodium 23 Which food additive is matched 29 Which of the following modern
chloride solution is added to correctly with its function? medicine can cause addiction?
solution Q, a white precipitate is A Streptomycin C Codeine
formed. Solution Q most likely ’11 B Paracetamol D Aspirin
contains Food Function 30 A patient complained of pain in
additive
I sodium stearate the stomach after taking aspirin.
A Thickener Tartrazine
II sodium palmitate ’08 Which substance will help to
B Flavouring Acasia gum
III lead(II) nitrate relieve the pain?
C Antioxidant Ascorbic A Ammonia
IV methyl ethanoate acid B Ethanoic acid
A I and II only C Sodium chloride
B III and IV only D Preservative Aspartame D Magnesium hydroxide
C I, II, and III only
D I, II, and IV only
Chemicals for Consumers 522
Structured Questions
1 The following equation shows the reaction between palm oil and concentrated potassium hydroxide solution. [1 mark]
’05 Palm oil + potassium hydroxide ⎯b⎯oil→ potassium palmitate + glycerol
[1 mark]
(a) What is the name of this reaction? [1 mark]
[1 mark]
(b) (i) Which of the chemicals in the above equation is a soap?
(ii) Name the homologous series to which palm oil belongs.
(iii) Complete the anion part of the palmitate ion.
CH2 CH2 CH2 CH2 CH2 CH2 CH2
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2
(c) Diagram 1 shows part of the washing action of a detergent particle, sodium alkyl sulphate on a cloth stained with
grease.
5
Diagram 1 [1 mark]
[1 mark]
(i) Write the anion part of sodium alkyl sulphate.
(ii) State the part of sodium alkyl sulphate that is soluble in grease. [2 marks]
(iii) Identify the particles represented by + and – in Diagram 1. [3 marks]
(iv) Based on Diagram 1, explain the cleansing action of detergents. [1 mark]
[1 mark]
(d) (i) State what happens to the grease particles on further agitation.
(ii) Complete Diagram 2 to illustrate your statement in (d)(i).
Diagram 2
2 A student carries out four experiments to study the effectiveness of two cleansing agents, X and Y, on an
oil-stained cloth in hard and soft water. Table I shows the arrangement of apparatus, the type of water used
and the observations for Experiments I, II, III and IV.
Experiment I II III IV
Arrangement of
apparatus
Observation Oily stains disappear Oily stains disappear Oily stains remain Oily stains disappear
Table 1
Chemicals for Consumers
523
(a) Based on the observation shown above, deduce (iii) How is ginger used to treat this illness?
which of the cleansing agents, X or Y, is [1 mark]
(i) a detergent, 4 (a) State three reasons why food additives are used
(ii) a soap? [2 marks] in the food industry. [3 marks]
(b) Describe the observation (if any) when solutions (b) Pineapple jelly contains gelatin.
X and Y are separately shaken with hard water. What is the role of gelatin in the jelly? [1 mark]
[2 marks] (c) Modern medicines are classified based on their
(c) Predict the observation if hard water in Experiment effects on the human body.
III is replaced by unpolluted river water. [1 mark]
Explain the terms analgesics and psychotherapeutic
(d) What inference can be drawn regarding the
drugs. [2 marks]
effectiveness of X and Y as cleansing agents?
(d) Complete the table to show the type of medicine
[2 marks] to which the following medicines belong to.
(e) State the variables involved in this experiment.
(i) Manipulated variable Name of medicine Type of medicine
(ii) Responding variable Aspirin
(iii) Constant variable [3 marks]
3 (a) Toothpaste contains the following chemicals: Barbiturate
Sodium lauryl sulphate: CH3(CH2)11OSO3Na Amphetamine
Calcium pyrophosphate: Ca2P2O7
Magnesium hydroxide: Mg(OH)2 Codeine
Silicon(IV) oxide: SiO2
5 Mint oil [4 marks]
Cellulose gum
Saccharin (e) State one side effect of taking (i) aspirin,
(ii) barbiturate for a prolonged period. [2 marks]
5 Aspirin has the following structural formula:
(i) What is the purpose of using sodium ’04
lauryl sulphate, mint oil and saccharin in
toothpaste? [3 marks]
(ii) In the food industry, cellulose gum is used as a
thickening agent. What is meant by thickening
agent? [1 mark]
(iii) Suggest a reason why magnesium hydroxide
is used in toothpaste. [1 mark]
(iv) State the names of chemicals needed for
the preparation of sodium lauryl sulphate.
[2 marks]
(v) Write the equations for the reactions.
[2 marks] (a) What is the molecular formula of aspirin? [1 mark]
(b) Ginger can be used as a traditional medicine. (b) Write the formulae of the ions produced when
Diagram 3 shows a ginger plant.
aspirin is added to water. [1 mark]
’06
(c) (i) State two observations for the reaction that
occurs when aspirin is added to sodium
carbonate solution. [2 marks]
(ii) Name one important application of aspirin.
[1 mark]
(d) State one side effect of aspirin. [1 mark]
(e) What is the correct way of taking aspirin? [1 mark]
(f) Give the name of a medicine that can be used
Diagram 3 as a substitute for aspirin. [1 mark]
(i) What illness can be cured by using ginger? (g) An aspirin pill contains 0.32 g of aspirin. Calculate
[1 mark] the volume of 0.050 mol dm–3 of sodium
(ii) Which of the parts W, X, Y or Z, is used to carbonate needed to neutralise the aspirin pill.
treat the illness in (i)? [1 mark] [3 marks]
(Relative atomic mass: H, 1; C, 12; O, 16)
Chemicals for Consumers 524
Essay Questions
1 (a) Describe one experiment to prepare a sample of (d) State three wrong methods of taking medicine
soap using coconut oil in the school laboratory. and the problems that may arise. [6 marks]
[8 marks]
(b) Describe four types of additives in liquid 3 (a) What is meant by food additives? [3 marks]
detergents. Give one example of the additives (b) A label on a box of ice-cream states that it
’08 contains the following food additives:
and state its function. [7 marks]
• Azo compounds
(c) Describe the differences between soaps and • Citric acid
• Benzyl ethanoate
detergents in terms of their effectiveness • Sodium benzoate
• Sucrose
as cleansing agents and their effects on the
environment. [5 marks]
2 (a) What is meant by (i) medicine and (ii) traditional
medicine? [3 marks] State the function of each of the food additives
(b) Give two examples of traditional medicine derived used. [12 marks]
from plants and state their functions. [2 marks]
(c) What are the advantages and disadvantages of
(c) Describe the types of modern medicine and
using food additives. [5 marks]
their examples. State the function of each type of
modern medicine. [9 marks]
5
Experiment
1 You are asked to devise an experiment to compare the effectiveness of the cleansing action of soaps and
detergents in soft water and hard water.
Your explanation must contain the following:
(a) Aim of experiment
(b) All the variables
(c) Statement of the hypothesis
(d) Lists of materials and apparatus
(e) Procedure of the experiment
(f) Tabulation of data [17 marks]
525 Chemicals for Consumers
PAPER 1 (50 marks) Time: 1 hour 15 minutes
Instructions: Question 1 to Question 50 are followed by four options A, B, C and D.
Choose the best option for each question.
1 The chemical used to coagulate I V 1.12 gram of acrolein contains Compound Relative
formula
latex into solid rubber is 1.2 3 1023 molecules. mass
A ammonia A I and III only
B methanoic acid B II and III only I CH3C6H2(NO2)3 227
C sodium chloride C I, II and III only 180
D calcium carbonate D I, II, III and IV II HOOCC6H4COOCH3 278
228
2 The element 14 X 5 Graphs I and II show the III FeSO4.7H2O
7 heating of two samples of
I has 5 valence electrons. naphthalene. IV Cu(NH3)4SO4
II is located in Period 3 of the A I, II and III only
B I, III and IV only
Periodic Table. C II, III and IV only
D I, II, III and IV
III forms a negatively charged temperature (°C)
ion of charge –3. graph I
IV has 7 protons and 14 7 Which of the elements below
neutrons. 80 X Y are inert?
A I and III only I: 2W III: 8Y
B II and IV only II: 4X IV: 10Z
A I and only
C I, II and III only time (s) III
graph II
D I, III and IV only temperature (°C) B I and IV only
3 The electronic configuration of C II and III only
the ion X2+ is 2.8.18.18.8. 80 P Q D II and IV only
The ion X2+ has 81 neutrons. 8 Brilliant blue is used as a food
Determine the nucleon number colouring. Its molecular formula
of the atom of element X. time (s) is C47H50N3O7S2 .
Calculate the number of moles
A 133 C 136 Why is the region XY of graph I
shorter than region PQ of graph of brilliant blue in 2.08 gram of
B 135 D 137 II?
A Sample II used is purer than the compound.
4 The diagram shows the
structural formula of the sample I. [Relative atomic mass: H, 1;
compound acrolein. B Sample I is heated earlier
C, 12; N, 14; O, 16; S, 32]
H2C == CH — C == O than sample II. A 0.0025 mol
| C Sample I is heated more B 0.0030 mol
H C 0.0050 mol
strongly than sample II. D 0.0060 mol
D Sample I is heated using a
Which statements below are 9 Which of the following
true concerning acrolein? water bath whereas sample II
is heated directly. hydrocarbons burns with the
[Relative atomic mass: H, 1;
C, 12; O, 16; Avogadro number 6 Which compound in the table most soot?
= 6 3 1023 mol-1] below is correctly matched with
I Acrolein is soluble in ethanol. its relative formula mass? [Relative atomic mass: H, 1; C, 12]
II Acrolein has a low melting
point. [Relative atomic mass: H, 1; C, AB CC25HH212 DC CC97HH1240
III Acrolein can undergo 12; N, 14; O, 16; Na, 23; P, 31;
addition polymerisation. S, 32; Ca, 40; Fe, 56; Cu, 64] 10 The table shows the proton
numbers of four elements P, Q,
R and S.
526
Element Number Number of 15 Which of the following metallic 19 Streptomycin is an antibiotic.
of protons neutrons Its molecular formula is
P oxides is amphoteric? C21H39N7O12.
Q 3 4 A Aluminium oxide, tin(II) oxide
R Calculate the number of
S 8 8 and lead(II) oxide streptomycin molecules contained
B Aluminium oxide, lead(II) in 1.162 gram of the compound.
9 10
oxide and silicon(IV) oxide [Relative atomic mass: H, 1;
11 12 C Magnesium oxide, tin(II) C, 12; N, 14; O, 16; Avogadro
number = 6 3 1023 mol–1]
Which of the following pairs oxide and lead(II) oxide A 1.2 3 1021 C 1.5 3 1022
of elements react to form a D Magnesium oxide, aluminium B 1.5 3 1021 D 1.5 3 1023
compound with the relative
formula mass of 54? oxide and tin(II) oxide
A P and Q
B P and R 16 Concentrated sodium chloride 20 Magnesium sulphate salt is used
C R and S solution is electrolysed using
D Q and R carbon electrodes. as laxative. 10 g of magnesium
11 The chemical that can be used At the anode, gas X is produced oxide is reacted with excess
to differentiate dilute sulphuric first followed by gas Y.
acid and dilute hydrochloric acid dilute sulphuric acid solution.
solutions is What is gas X and gas Y?
I sodium carbonate solution Calculate the maximum mass
II silver nitrate solution
III lead(II) nitrate solution Gas X Gas Y of magnesium sulphate salt
IV barium nitrate solution A Oxygen Chlorine
A I and III only B Oxygen Hydrogen formed.
B II and IV only C Chlorine Hydrogen
C I, II and IV only D Chlorine Oxygen [Relative atomic mass: O, 16;
D II, III and IV only
Mg, 24; S, 32]
A 12 g C 24 g
B 28 g D 30 g
21 X and Y form a covalent
17 Potassium iodide solution of compound with the formula YX3.
concentration 1 mol dm–3 Which of the following is the
is electrolysed using carbon
electrodes. likely proton numbers of X and
Which of the following half- Y?
equations represent the reactions
12 20.00 cm3 of sulphuric acid occurring at both electrodes? Proton Proton
number of number of
neutralises 25.0 cm3 of 2 mol atom X atom Y
dm–3 sodium hydroxide solution. Anode Cathode A 13 9
2H+ + 2e–
Calculate the concentration of A 4OH– → → H2 B 17 13
2H2O + O2
the sulphuric acid solution in + 4e– 2H+ + 2e– C 15 17
→ H2
mol dm–3. B 2I– → 2I– → D 17 15
A 0.40 mol dm–3 I2 + 2e– I2 + 2e–
B 0.80 mol dm–3 4OH– → 22 The diagram below shows a
C 1.25 mol dm–3 C 2H+ + 2e– +2H42eO– + O2 chemical cell.
D 2.50 mol dm–3 → H2
A
13 As we go down Group 1, D 2H+ + 2e–
A reactivity decreases → H2 zinc iron
B electropositivity decreases
C melting point decreases 18 Calculate the volume of oxygen
D density decreases
gas needed for complete
14 Which of the following sodium
statements is true about combustion of 3.2 g of methane chloride(aq)
halogens? at room temperature and How can the voltage of the cell
A Chlorine is more reactive be increased?
pressure. I Increase the concentration of
than fluorine. sodium chloride solution
B Iodine reacts with iron to [Relative atomic mass: H, 1; C, II Replace the iron electrode
with copper electrode
produce iron(III) iodide. 12; 1 mol of gas occupies 24 III Replace the sodium chloride
C Bromine exists as gas at room solution with iron(II) sulphate
dm3 at r.t.p.] solution
temperature and pressure. A 2.4 dm3
D Bromine is more B 4.8 dm3
C 9.6 dm3
electronegative than chlorine. D 12.0 dm3
527
volume II volume I time
of of II
IV Replace the zinc electrode volume
I Sodium iodidCeO2s(oclmu3ti)on C vColOum2 (ecm3) II time of
with magnesium electrode time CO2 (cm3)
A I and III only II Potassium sulphate solutioI n of I
B II and IV only CO2 (cm3) I
C I, II and IV only III Hydrochloric acid solution
D II, III and IV only
IV Ammonia solution
A I, II and III only time
B I, II and IV only
D volume
23 Which of the following is a C II, III and IV only
of
composite material? D I, II, III and IvVolume CO2 (cm3) II
A Fibreglass of
B Borosilicate glass 29 The diagram I
C Lead glass shCoOw2 s(cmso3)me
D Soda glass 50
cents coins. II
24 The bite of fire ants contains the time time
compound with the molecular 31 The diagram below shows a
formula HCOOH. graph obtained when hydrogen
Which of the following chemicals peroxide decomposed to oxygen
can be used to counter the The composition of elements in when manganese(IV) oxide is
added into the solution.
effect of this chemical? the coins are
A Ethanoic acid A 10% tin and 90% copper volume of
B Ethyl ethanoate B 30% zinc and 70% copper oxygen gas
C Sodium bicarbonate C 50% tin and 50% lead V (cm3)
D Ethanol D 25% nickel and 75% copper
25 10.0 gram of sodium hydroxide 30 The table shows the volumes 90 150 time
is dissolved in V cm3 of distilled and concentrations of (s)
hydrochloric acid added to
water. 10 g of marble (in excess) in From the graph we can
experiments I and II.
The solution obtained has a conclude that
concentration of 0.5 mol dm–3. I the rate of decomposition of
Calculate the value of V.
[Relative atomic mass: H, 1; hydrogen peroxide decreases
O, 16; Na, 23] Experiment Volume of Concentration with time.
A 200 cm3 C 500 cm3 hydrochloric of hydrochloric II the average rate of
B 250 cm3 D 1000 cm3 acid (cm3) acid
(mol dm–3) decomposition of hydrogen
peroxide is —9V—0 cm3 s—1.
26 Which of the solutions below I 50 1.0 III the rate of reaction at time
II 100 0.5
has the lowest pH value? 150 second is zero.
A 25 cm3 of 1.0 mol dm–3
Which of the following graphs of IV all the hydrogen peroxide
sulphuric acid
B 25 cm3 of 1.5 mol dm–3 total volumes of carbon dioxide had decomposed at 90
nitric acid collected against time for both seconds.
C 25 cm3 of 2.0 mol dm–3
experiments I and II is correct? A I, II and III only
ethanoic acid
D 45 cm3 of 1.0 mol dm–3 A volume B I, III and IV only
hydrochloric acid of II volume C III,I, III and IV only
CO2 (cm3) of II, III aInI d IV
CO2 (cm3)D
I 32 T2hSeO2r(agte) + Oth2e(ga)b→ove2SreOa3c(tgio)n
of
27 nCHCH3CH2 →I -(CHCH3CH2)n-
The reaction I represented by above can be increased by
the equation above is time A adding vthanetaimrdeeiaucmtiopnovwedseser.l.
B cooling
A cracking
B C increasing the pressure.
B polymerisation
raeddduitciotinonreraecatCovciooftOilnou2m n(cem3) oCvofvoCOlofuO2lmu(2cme(mcem3)3) I I volume D immediately removing the
C II of suIlIphur Itrioxide formed.
D CO2 (cm3)
II
33 Which of the following
28 Which of the following reagenIts
can be used to differentiate II compounds does sulphur have
lead(II) nitrate and aluminium the highest oxidation state?
nitrate solutions?
time titmimee BA SHO2S2 timeDC HH22SSO2O37
volume I volume 528 I
of
CO2 (cm3) of II
CO2 (cm3)
34 W, X, Y and Z are four metals. III M x+ ion accepts electron acid, the heat energy released
during the reaction. increases the temperature of the
Consider the reactions below acid to y oC. Determine the heat
IV M x+ ion releases electron of reaction between zinc and
involving these metals: during the reaction. hydrochloric acid.
X + Z sulphate → [Relative atomic mass: Zn, 65;
A I and III only C II and III only Specific heat capacity of water
Z + X sulphate B I and IV only D II and IV only = 4.2 J/g oC]
W + Z sulphate → A —16——.5—3 3 100 3 4.2 3
Z + W sulphate 38 The diagram below shows (y – x) kJ/mol
W + X sulphate → three iron nails wrapped with B —16——.5—3 3 —1——1——00——00——0— 3 4.2 3
No reaction metals P, Q and R and then (y – x) kJ/mol
Y + Z sulphate → left in agar-agar solution added C —16——.—53 3 100 3 4.2 3
No reaction with a few drops of potassium (y – x) kJ/mol
Arrange the metals W, X, Y hexacyanoferrate(III) for 1 day. D —16——.5—3 3 —1——1——00——00——0— 3 4.2 3
(y – x) kJ/mol
and Z in decreasing order of agar-agar solution + a few drops of potassium
hexacyanoferrate(III) 41 Which of the following
electropositivity. statements is not true
A X, W, Z, Y C W, X, Z, Y I II III concerning soap?
B Y, Z, W, X D Y, Z, X, W A Soap does not pollute
river water because it is
35 P Alkene Q biodegradable.
Alcohol B Cleansing action of soap is
not affected in acidic water
Alkane S Chloroalkane iron nail + P iron nail + Q iron nail + R but the cleansing action of
soap is lower in hard water.
An alcohol can be converted to The results of the experiment C Soap is produced by alkaline
chloroalkane via three processes are tabulated below: hydrolysis of fat molecules.
P, Q and R. D Part of the soap molecule
Test tube Observation dissolves in greasy stain
Name the processes P, Q and and a part of the molecule
R. I Large amount dissolves in water.
of dark blue
PQR precipitate formed
A Fermentation Hydrogenation Substitution II No dark blue
precipitate formed
B Fermentation Hydrolysis Substitution
III Small amount
C Dehydration Hydrogenation Hydrolysis of dark blue
precipitate formed
D Dehydration Hydrogenation Substitution
Arrange the metals P, Q and
36 The IUPAC name for the R in decreasing order of 42 The diagram shows the content
compound shown below is electropositivity. of a box of ice cream.
A P, R, Q C Q, R, P
C2H5 B P, Q, R D Q, P, R Contents : Vanillin, Lecithin,
Sugar, Full cream milk
CH3CHCH2CHCH3 39 The heat of combustion of an Manufactured date :
Sept 2012
C3H7 alkane X is 2020 kJ mol–1.
A 2,4-dimethyloctane When 11 g of the alkane X is
B 3,5-dimethyloctane
C 2-ethyl-4-methylheptane burned, 505 kJ of heat is released.
D 2-ethyl-4-propylpentane
Determine the molecular What is the function of vanillin
37 Mx+ → My+ and lecithin?
The element M has two formula of alkane X.
oxidation numbers. The [Relative atomic mass: H, 1; C, 12] Vanillin Lecithin
conversion of Mx+ to My+ is a A Emulsifier Colouring
reduction reaction if AB CC32HH68 CD CC54HH1102 B Emulsifier Flavouring
I the value of x is more than C Flavouring Colouring
40 The initial temperature of D Flavouring Emulsifier
y. 100 cm3 dilute hydrochloric acid
II the value of y is more than solution is x °C. When 1.3 g of
zinc powder is added to the
x.
529
43 Which of the following medicine is correctly categorised? 48 Which of the statements below
are true?
Analgesic Antibiotic Psychotherapeutic
I Vulcanised rubber is more
A Streptomycin Colouring Valium
elastic than natural rubber.
B Aspirin Flavouring Codeine
II Vulcanised rubber is less
C Paracetamol Streptomycin Ketamine
stretchable than natural
D Aspirin Insulin Barbiturate
rubber.
44 The table shows the proton Which of the following
numbers of four elements. experiments will produce graph III Vulcanised rubber is harder
Q?
Element WX Y Z than natural rubber
Experiment Manipulated variable
Proton number 9 11 17 19 IV The melting point of
I 5 grams of zinc
powder added to vulcanised rubber is higher
50 cm3 of 0.5 mol
dm–3 HCl at 30 °C than natural rubber.
A I, II and III only
II 5 grams of B I, III and IV only
granulated zinc C II, III and IV only
added to 25 cm3 of D I, II, III and IV
1.0 mol dm–3 HCl at
Which of the following pairs 30 °C 49 The diagram shows an
apparatus set-up of an
of elements reacts most III 5 grams of experiment used to prepare gas
granulated zinc X.
vigorously? added to 50 cm3 of
A W and Z 0.5 mol dm–3 HCl at mineral wool aluminium
B X and Y 40 °C soaked oxide
C X and Z in ethanol gas X
D W and X IV 5 grams of
granulated zinc
45 When a mixture of bromine added to 50 cm3 of heat water
1.0 mol dm–3 HCl at
water, potassium iodide and 30 °C Which of the statements below
is true about gas X?
carbon tetrachloride is shaken, A I and III only A Rekindle a glowing splint
B II and IV only B Decolourises brown colour of
I the iodide ions will be C I, II and III only
D I, III and IV only bromine water
oxidised. C Produces a ‘pop’ sound when
II redox reaction will take place. tested with a burning splint
D Changes colour of acidified
III iodide ions act as reducing
potassium dichromate from
agent.
orange to green
IV the carbon tetrachloride layer
will turn brown.
A I, II and III only
B I, III and IV only
C II, III and IV only
D I, II, III and IV
46 The diagram shows graph P 47 Consider the reaction:
obtained when 5 grams (in
excess) of granulated zinc is phosphoric potassium acidified
added to 50 cm3 of 0.5 mol acid dichromate(VI)
dm–3 hydrochloric acid at 30 oC. potassium
C3H6 + steam ⎯⎯→ X ⎯⎯⎯→ Y dichromate(VI) butanol
What is the molecular formula 50 CTh3He7fOloHwc⎯ha⎯rt ⎯ab→oveA ⎯⎯→ B
of X and Y? shows
total volume P XY the conversion of C3H7OH to
of H2 (cm3) products A and B.
Q
A C3H7OH C3H7COOH What of the following is the
B C3H7OH C2H5COOH
C C3H6(OH)2 C3H7COOH molecular formula of product B?
D C3H6(OH)2 C2H5COOH
time (s) CBDA CCCC2332HHHH7575CCCCOOOOOOOOCCCC4343HHHH9779
530
PAPER 2 Time: 2 hour 30 minutes
Section A (60 marks)
Answer all questions in this section.
The time suggested to complete this section is 90 minutes.
1 Table 1 shows a list of elements labelled P, Q, …… phenolphthalein (b) Two drops of
V. phenolphthalein is
nitric acid added
The letters are not the actual symbols of the into the sodium
elements. 20 hydroxide solution.
20
Element 7 P 162Q 174R 168S T27 U V35 40 (c) A burette is filled
3 20 with nitric acid of
13 17 20 30 concentration 2.0
30 mol dm–3.
Electronic The initial burette
configuration reading is 0.00 cm3.
The sodium
Table 1 hydroxide in the
conical flask is then
(a) Write the electronic configuration of the elements titrated with the
nitric acid until the
in the spaces provided. [1 mark] neutral point.
(b) (i) Complete Table 2 below by writing the (d) Diagram shows
formula of the compound formed between the final burette
a pair of elements given. reading.
(ii) State whether the compound formed is
ionic or covalent.
(iii) Determine the relative formula mass of the
compound.
Pair of Formula of Ionic or Relative
elements compound covalent formula mass
Q and S
P and R Table 2 [7 marks] 30
T and U
R and U Diagram 1
V and R
Q and U (a) Name the apparatus P used in measuring
T and S
25.0 cm3 of the sodium hydroxide solution.
(c) Hydrogen (H) and R form a covalent compound. [1 mark]
Draw the Lewis structure of this compound. (b) State the colour change of the phenolphthalein
[2 marks] indicator at the neutral point. [1 mark]
2 Diagram 1 shows the steps involved in preparing a (c) (i) State the volume of nitric acid needed to
neutralise the sodium hydroxide solution.
salt.
[1 mark]
(a) 25.0 cm3 of
P sodium hydroxide (ii) The experiment is repeated by adding
solution of this volume of nitric acid in (c)(i) above
sodium concentration to 25.0 cm3 sodium hydroxide solution
hydroxide 2.0 mol dm–3 is of concentration 2.0 mol dm–3 without
measured using addition of phenolphthalein indicator.
apparatus P and
then transferred Why was the experiment repeated without
into a conical flask. the addition of phenolphthalein indicator?
Write the chemical formula of this
compound. [1 mark]
531
(d) (i) Write a balanced equation for the 0.2 g of lithium was added into 200 cm3 of water in
a conical flask at room temperature and pressure.
neutralisation reaction. [1 mark] The gas collected was recorded at 20-second intervals.
The result was tabulated below:
(ii) Calculate the maximum mass of salt
formed.
[Relative atomic mass: N, 14; O, 16;
Na, 23] [2 marks] Time (s) 0 20 40 60 80 100
0 250 310 355 360 360
(iii) State one use of this salt. [1 mark] Gas syringe
reading (cm3)
(e) The salt formed remained in the solution. Describe
how the salt is removed from the solution.
[2 marks] (a) Write a chemical equation for the reaction
3 The flowchart below shows the steps involved in the between lithium metal and water. [1 mark]
production of ammonia in industry.
(b) Sketch a graph of volume of gas evolved against
time. [3 marks]
Unreacted nitrogen volume
and hydrogen of gas
(cm3)
Nitrogen Catalyst Ammonia
chamber
Compression
chamber
Hydrogen Liquid ammonia
(a) How are (i) nitrogen (ii) hydrogen obtained? time (s)
[2 marks]
(b) To what pressure is the mixture of nitrogen and
hydrogen compressed? [1 mark] (c) (i) State how the reaction rate changes with
(c) Name the catalyst used in the catalyst chamber. time. [1 mark]
[1 mark]
(ii) Explain your answer. [1 mark]
(d) To what temperature is the catalyst heated?
[1 mark] (d) Calculate the number of moles of gas collected.
(e) After all these conditions are attained, the [1 mol of gas occupies a volume of 24 dm3 at
nitrogen and hydrogen react to form ammonia. room temperature and pressure] [2 marks]
Write a equation for the reaction. [1 mark]
(f) How is the liquid ammonia removed from the
reaction chamber? [1 mark]
(g) State two uses of ammonia. [2 marks]
4 Diagram 2 shows the apparatus set-up used to
study the rate of reaction between lithium metal and
water.
(e) The experiment was repeated as stated below:
hydrogen gas Experiment II : 0.2 g of lithium was added to
200 cm3 of water at 40 °C.
Experiment III : 0.1 g of lithium was added to
conical burette 200 cm3 of water at 30 °C.
flask
lithium Sketch the shape of the graphs for each of these
experiments on the same axes as graph (b)
above. [2 marks]
Diagram 2 5 Diagram 3 shows the apparatus set-up to study the
reactivity of metals P, Q, R and S with oxygen.
532
potassium glass Metal P (d) Identify the metal
chlorate, KCIO3 wool (i) P (ii) S [2 marks]
(e) (i) Identify metal Q : [1 mark]
(ii) Name the product formed when metal Q
heat heat was used in the reaction. [1 mark]
(iii) Write a chemical equation for this reaction.
[1 mark]
Diagram 3 (f) Suggest another experiment which can be carried
The P metal powder was heated strongly first. Then out to determine the position of the metals in
the potassium chlorate was heated. On heating, the
potassium chlorate decomposes to give oxygen gas. the reactivity series. [1 mark]
The reactivity of the reaction between the hot metal
and oxygen gas was recorded. The experiment was 6 Table 3 below shows four categories of medicine.
repeated by replacing P metal powder with Q, R and
S metal powders. Category Example
The result of the experiment is shown in the table P Streptomycin
below:
Q Valium
Results
R Aspirin
Hormone Insulin
Table 3
Metals Observation Colour of product formed (a) Name the category of the following medicine
when…
(i) Streptomycin (iii) Aspirin
Hot Cold (ii) Valium [2 marks]
P Burns brightly Yellow White (b) State the function of each category of medicine.
(i) P (ii) Q (iii) R [3 marks]
Q Glows dimly Black Black
(c) (i) Name a disease that can be treated with
R Burns very White White
brightly streptomycin. [1 mark]
S Glows brightly Brown Yellow (ii) A patient must complete the dosage of
streptomycin prescribed by the doctor.
(a) What is the function of the glass wool in the Explain why. [1 mark]
experiment? [1 mark] (d) (i) Aspirin cannot be prescribed to small
(b) Write a balanced chemical equation for the children. Explain why. [2 marks]
decomposition of potassium chlorate when (ii) Name an alternative medicine to aspirin for
heated. [1 mark] small children. [1 mark]
(c) Arrange the metals P, Q, R and S in decreasing (e) Valium cannot be used for prolonged period.
order of reactivity. [2 marks] State a reason why. [1 mark]
Section B (20 marks)
Answer any one question from this section.
The time suggested to complete this section is 30 minutes.
7 (a) Table 4 shows the products formed at the (ii) Using half-equations, explain how these
carbon electrodes when dilute and concentrated products are formed at the electrodes.
sodium chloride are electrolysed.
[10 marks]
Electrolyte Electrodes Products at
Anode Cathode (b) Electroplating can be used to coat an iron chain
with a thin coat of silver.
Explain how you carry out the process. [7 marks]
Dilute sodium chloride Carbon Gas P Gas Q 8 (a) Starting with magnesium oxide, describe how you
solution
can prepare a sample of magnesium carbonate
Concentrated sodium Carbon Gas R Gas S salt. [10 marks]
chloride solution
(b) You are given four solutions each containing
Table 4 sulphate, nitrate, carbonate and chloride ions.
Describe experiments on how you can identify
(i) Name the gases P, Q, R and S released at the ions present in each solution. [10 marks]
the electrodes. [3 marks]
533
Section C (20 marks)
Answer any one question from this section.
The time suggested to complete this section is 30 minutes.
9 (a) With the aid of an energy level diagram, explain (c) Describe an experiment to determine the heat
the meaning of of precipitation of silver chloride. Your answer
(i) exothermic reaction should include:
(ii) endothermic reaction [6 marks] (i) Procedure of experiment
(ii) Tabulation of result
(b) Table 5 shows the heat of displacement (iii) Calculation [8 marks]
Displacement reaction Heat of 10 (a) Using pentane as an example, define the term
displacement
(kJ mol–1) isomerism. [5 marks]
(b) With an example, explain the meaning of
23MFCeAZug(nl(((ss(ss))s)))+++++CF23ueAAZSSl2ngOO(NSS44OOO((aa434(qq()aa))3q(qa→))q→→) ΔH1 substitution reaction. [6 marks]
2Ag(s) + Mg(NO3)2(aq) ΔH2
Table 5 ΔH3 (c) X =anCd6YH1a2re two Y = C6H14
X organic compounds.
(i) Write the general formula of each
compound. [2 marks]
(ii) Describe an experiment on how you can
differentiate both compounds. [5 marks]
(iii) X can be converted to Y.
Arrange the values of the heat of displacements Name the reaction of this conversion.
of the three reactions above in increasing order. [1 mark]
[2 marks] Write a chemical equation for the reaction.
Explain your answer above. [4 marks] [1 mark]
Paper 3 (50 marks) Time: 1 hour 30 minutes
Instructions: Answer all questions. below the water level. A thermometer is placed in
the boiling tube.
1 Diagram 1 shows the apparatus set-up to determine
the melting point of a substance X. (d) The water bath is heated with a slow fire.
thermometer retort stand (e) After some time the stopwatch is started and the
temperature of the substance X is recorded at
boiling tube 30-second intervals.
beaker
(f) The diagram below shows the temperature
substance X readings of the substance at 30-second intervals.
water
80 80 80 80 80 80
70 70
heat tripod stand 80 80
Diagram 1 70 70 70 70
(a) 3 spatulas of substance X are added into a boiling Time: 0 minute Time: —12— minute
tube. Temperature = Temperature =
(b) A 500 ml beaker is filled with water until it is 80 80
a bout —34— -full and placed on a tripod stand.
(c) The boiling tube containing substance X is then
clamped in the water bath with the substance X
534 80 80
8800 80 8080 80 80 8800 (a) 80Rpreocvoidrdedt.h e temperature80reading in the spaces
80 80 80 80 [3 marks]
(b80) 8C0onstruct a table to tabulate the results of the
experiment above. [3 marks]
(c) Plot a graph of temperature against time. [3 marks]
(d) Explain why a water bath is used to heat substance
X. [3 marks]
7700 70 7070 70 70 7700 (e) 70What can you say abou7t0 the temperature from
Time: 1 mi7n0ute70 Time: 17—120— 70 70 7 t0ime 1 minute to 212— minutes? [3 marks]
Temperature = Explain your answer.
minutes
Temperature = (f) 90 (i) What is the melting90point of substance X?
[3 marks]
80
8800 80 8800 80 80 80 (ii) If the melting point of substance X from
80 80
another laboratory is determined and is
80 80 80 80
80 80 found to be lower than this value, what can
you say about the sample? [3 marks]
7700 70 7700 70 70 2 Diagram 2 below shows the apparatus used in an
9800 80 70 exp8e0riment carried out in 8th0e school laboratory to
70 70 study the property of oxide of elements in Period 3 of
Time: 2 min7u0te7s0 70 the Periodic Table.
Temperature =
Time: 270—21—70minutes 70 70 magnesium magnesium
9900 90 Temperature = glass omxaidgenesium moxaidgenesium
rgoladss oxide oxide
80 80 90 90 rod90 90 glass
80 rgoladss
90 90 rod
80
8700 70 8800 80 80 80 nitric acid after sodium MgO after
nitric acid satifrtreinr g hsyoddroiuxmide MgO satifrtreinr g
70 70 80 80 80 80 stirring hydroxide stirring
70 70
Experiment I
Time: 3 minutes Time: 3—21— minutes
Temperature = Temperature = Observation :
90 glass silicon(IV) glass silicon(IV)
groladss soixliicdoen(IV) groladss osixliicdoen(IV)
rod oxide rod oxide
90
80 80 SiO2 after sodium after
sodium hydroxideSiO2 satifrtreinr g hsyoddroiuxmide satifrtreinr g
Time: 4 minutes stirring hydroxide stirring
Temperature = sodium hydroxide
Experiment II glass aluminium
Observation : aaoxlluuidmmeiinniiuumm rgoladss oaxluidmeinium
rod oxide
oxide
glass
rgoladss
rod
535
stirring hydroxide stirring
aluminium aluminium (b) Record your observations in the spaces provided.
oxide oxide
[3 marks]
glass glass (c) What conclusions can you make from the result of
rod rod
the experiment above? [3 marks]
(d) Name another oxide that has the same property
as
(i) magnesium oxide :
(ii) silicon(IV) oxide :
(iii) aluminium oxide : [3 marks]
nitric acid after sodium after 3 “Cleansing power of soap is lower in hard water
stirring hydroxide stirring
whereas the cleansing power of detergent is unaffected
Experiment III in hard water”.
Observation :
Describe an experiment to prove the above
statement.
Diagram 2 Your planning should include the following:
The oxides of the elements are added into dilute nitric (a) Problem statement
acid and dilute sodium hydroxide.
(b) Hypothesis
The mixtures are stirred. The results are shown in
Diagram 2. (c) Variables of the experiment
(d) Apparatus and chemicals used in experiment
(a) State three variables that must be kept constant (e) Procedure of experiment
in the experiment. (f) Tabulation of result [17 marks]
[3 marks]
536
Answers
Form 4 Structured Questions (ii) Volume of water
1 Introduction to Chemistry 1 (a) (i) Concentration of hydrochloric (iii) Mass of salt that dissolved in
acid solutions 100 cm3 of water 3
Self Assess 1.1 (ii) Time taken for the 5 cm (c)
1 Field
Chemicals used length of magnesium ribbon
to dissolve
Agriculture Fertilisers and pesticides (iii) The length of magnesium
Medicine Antibiotics and analgesic ribbon 3
drugs
(b) The higher the concentration of
Food Food preservatives and the hydrochloric acid solution,
processing food flavourings the shorter the time taken for
Self Assess 1.2 the magnesium ribbon to
1 (a) Table salt is soluble in water but
dissolve. 1
not in kerosene.
(b) (i) Manipulated variable: (c) (i)
Solvents used, that is, water 4 F
and kerosene O
(ii) Responding variable: (d) (i) The solubility of the salts R
Solubility of table salt M
(iii) Constant variable: increases with the increase 4
Volume of solvent
(c) Apparatus: Two test tubes, glass in the temperature of the
rod, 10 cm3 measuring cylinder,
electronic balance, filter paper water.
and spatula.
Materials: Water, kerosene and (ii) The solubility of salt Q is
table salt.
(d) (i) 2 grams of table salt is higher than that of salt P. 2
weighed onto a filter paper.
(ii) 5 cm3 of water is measured 3 (a) The higher the temperature of
using a measuring cylinder and
then poured into a test tube. the water, the greater the mass
(iii) The salt is added to the
water and the mixture is 5 of sugar that can dissolve in
stirred using a glass rod.
(iv) The procedure above is it. 1
repeated by adding 2 grams
of salt to kerosene and (ii) 0.425 mol dm–3 1 (b) (i) Temperature of water
stirred.
(e) 2 (a) Volume of water 1 (ii) Mass of sugar that dissolves
(b) (i) Temperature of water (iii) Volume of water 3
3 (c) Temperature of Initial mass of beaker Final mass of beaker Mass of sugar CHAPTER 1
water (°C) P and contents (g) P and contents (g) dissolved (g)
Solvent Water Kerosene 30 92.50 87.50 5
40 87.50 77.50 10
Solubility of salt Soluble Not soluble 50 77.50 62.50 15
60 62.50 42.50 20
Self Assess 1.3 70 42.50 17.50 25
1 (a) Add concentrated acid to the water.
2
(b) Make sure the mouth of the
test tube is not directed at any (d) tartrazine) and food enhancer
student.
(i.e. monosodium glutamate). 4
(c) Carry out the experiment in a
fume cupboard. (b) Pharmacist, dentist, agriculturist,
chemical engineer, biochemist
SPM Exam Practice 1 and geologist. 6
Multiple-choice Questions
(c) The government can collect tax
1 B 2 D 3 C 4 A 5 A
6 B 7 C 8 D 9 A 10 D from the export of these chemicals.
11 A 12 C 13 A 14 B 15 C
16 C 17 A 18 B 19 B 20 B 3 Jobs are created by these
21 D 22 C 23 A 24 D 25 B
26 D 27 A 28 D (e) 12.5 gram 1 industries.
4 (a) Food preservatives (i.e. potassium The country saves on foreign
nitrate), antioxidant (i.e. ascorbic exchange if the chemicals needed
acid), food colouring (i.e. are produced locally. 3
537 Answers
(d) Cooperate with fellow classmates (b) (i) Making an observation, Responding variable Mass of salt
when carrying out an experiment. making an inference, making that dissolved
Be honest in recording the results a hypothesis, identifying Constant variable
obtained in the experiment. variables, planning the Temperature of water 3
Do not waste chemicals and only procedure of the experiment, (d) Apparatus 100 cm3 measuring
take the required amount needed carrying out an experiment, cylinder, electronic balance,
for the experiment. collecting data, interpreting 100 cm3 beaker and spatula.
Always follow safety procedures data and making a conclusion. Materials Water and common
while carrying out an experiment. 8 salt. 3
Clean the apparatus after carrying (ii) An inference is an initial (e) Procedure
out an experiment. 5 opinion based on an (i) Initial mass of beaker A and
(e) Urea as nitrogenous fertiliser to observation. salt is taken (x g).
enhance growth. Paraquat as a A hypothesis is a statement (ii) 50 cm3 of water is measured
using a measuring cylinder
herbicide to kill the weeds which that relates a manipulated and poured into a 100 cm3
compete with the crop for variable to a responding
nutrients from the ground. 2 variable. An experiment has beaker.
Essay Questions to be carried out to prove the Salt is added to 50 cm3 of
1 (a) Apparatus Two test tubes, two
validity of the hypothesis. 4 water a little at a time while
rubber stoppers, test tube rack,
sandpaper, 100 cm3 beaker, Bunsen (iii) In graphical form, a pie stirring the mixture until
no more salt can further
chart or tabulation. 6
burner, tripod stand and wire gauze. Experiments dissolve.
Materials Water, iron nails,
1 (a) To determine the effect of the (iii) The final mass of beaker A
cooking oil. 3
F volume of water on the solubility and salt is taken (y g).
O (b) (i) Water with air and water
R of salt 3 The mass of salt that
M without air
4 (b) The greater the volume of water, dissolved is (x – y) gram.
(ii) Rusting of iron nail
the greater the amount of salt (iv) The experiment is repeated
(iii) Presence of water in both sets
that dissolves. 3 by dissolving the salt in
of experiments 3
(c) Manipulated variable Volume of 30 cm3, 40 cm3, 60 cm3 and
(c) Procedure
water 70 cm3 of water. 3
(f) Tabulation of data
Volume of Initial mass of beaker Final mass of beaker Mass of salt
water (cm3) A and contents (g) A and contents (g) dissolved (g)
30 x y (x –y)
CHAPTER 1 & 2 (i) Two iron nails are cleaned 40
with sandpaper. 50
60
(ii) A 100 cm3 beaker is filled 70
with water. The water is
heated until boiling to expel 3
the air from the water.
2 (a) Manipulated variable (d) (i) pH = 13.55
(iii) The boiled water is then
poured into test tube A. Concentration of NaOH solution (ii) 0.25 mol dm–3 3
(iv) Cooking oil is poured onto Responding variable pH value 3 (a) (i) Mass of catalyst
the water in test tube A to
prevent air from dissolving in Constant variable (ii) Time taken to collect 50 cm3
the water.
Volume of solution 3 of oxygen gas
(v) Tap water is poured into test
tube B. (b) The higher the concentration of (iii) Volume and concentration of
(vi) An iron nail is then dropped sodium hydroxide solution, the hydrogen peroxide solution
into each of the tubes above
higher the pH value. 3 3
and left for three days. 10
(d) Results (c) (b) The greater the quantity of
catalyst added, the shorter the
time taken to collect 50 cm3 of
oxygen gas. 3
Test tube A B 2 The Structure of the Atom
Observation Iron nail does Iron nail Self Assess 2.1
after 3 days not rust rusts 1 (a) Molecules
(b) lons
4 (c) Atoms
(d) lons
2 (a) Scientific method is a systematic (e) Atoms
(f) Molecules
approach taken when carrying out
scientific research. 2 3
Answers 538
2 (a) T2 3 Carbon-14, 146C. (b) t3 minute 1
(b) Mixture of solid and liquid Radioisotope is an isotope that is (c) 115 °C 1
unstable and will decay by emitting
naphthalene. radioactive rays. Carbon-14 is used (d) Heat is absorbed to overcome
(c) The heat is absorbed to in dating the age of archaeological
artifacts. the forces of attraction between
overcome the forces of attraction
between the naphthalene Self Assess 2.4 the solid particles.
molecules. 1
(d) Heat absorbed is equal to the
heat supplied in heating. 1
(e)
2 (a) (i) Five valence electrons
Self Assess 2.2 (ii) 15 protons. (Number of
1 (a) Proton number = 92
protons is equal to the total 2
Nucleon number = 92 + 143 Y: 2.8.1
= 235 number of electrons) 3 (a) V: 2.4 W: 2.6 X: 2.6
Z: 2.8.6 2
Nuclear symbol is 23952U. (b) Nucleon number
(b) It has 53 protons and 53 (b) Four 1
= Number of protons +
electrons. (c)
Nucleon number Number of neutrons
= proton number +
= 15 + 16 = 31
number of neutrons
127 = 53 + number of neutrons (c) X31 F
Number of neutrons O
= 127 – 53 15 R
= 74 M
The 53 protons and 74 neutrons SPM Exam Practice 2 2 4
are located in the nucleus of the Multiple-choice Questions
atom, whereas the electrons are 1 C 2 C 3 B 4 D 5 B (d) Three electron-filled shells. 1
arranged in shells surrounding the 6 B 7 B 8 A 9 C 10 A
nucleus. 11 B 12 B 13 D 14 A 15 C (e) Nucleon number is the sum of
2 (a) B and E are atoms of the same 16 C 17 B 18 C 19 A 20 D
element because they have the 2 1 D 22 C 23 A 24 B 25 C the number of protons and the
same proton number. 26 B 27 D 28 A 29 B 30 D
(Note: Atoms of different 31 C 32 A 33 C 34 A 35 D number of neutrons. 1
elements have different proton 3 6 B 37 B 38 D 39 A 40 C
numbers) (f) 23 – 11 = 12 neutrons. 1
(b) Al is the symbol for aluminium. It Structured Questions
has 13 protons, 13 electrons and 1 (a) (i) (g) (i) Isotopes are atoms with the
14 neutrons (27 – 13 = 14).
(Note: In a neutral atom, the Atom Proton number Nucleon number same proton number but
number of protons is equal to the
number of electrons) 12 C 6 12 different nucleon numbers. CHAPTER 2
6 14
2
14 C 6 (ii) W and X. 1
6
2 4 (a) Bromine and naphthalene. 1
(ii) 126C has six neutrons while 146C (b) Iron 1
has eight neutrons. 1 (c) (i) Iron 1
(b) (ii)
Self Assess 2.3
1 Isotopes are atoms with the same
number of protons but different
number of neutrons. 2 1
Each has 92 protons. The number (c) In carbon dating: To determine (d) Sodium ions and chloride ions 1
of neutrons in each isotope are 142, the age of archaeological (e) (i) T1 1
(ii) The heat is absorbed to
143 and 146 respectively. specimens. 1
overcome the forces of
(Note: The number of neutrons are (d) 4 valence electrons 1 attraction between the
obtained by deducting the proton 2 (a) (i) Solid naphthalene molecules. 2
number from the nucleon number) (ii) Mixture of solid and liquid (iii) The speed of movement of
the particles increases during
2 B127 and E131 are isotopes because (iii) Liquid
53 53 heating from R to S. 1
they have the same proton number
(iv) Mixture of liquid and gas
but different nucleon numbers.
(v) Gas 3
539 Answers
Essay Questions (ii) Nucleon number is the total
1 (a) Solid Liquid Gas number of protons and
neutrons in the nucleus of an
P ar ticle Particles are The particles are The particles are 2 atom. 1
arrangement closely packed. still closely packed very far apart. (iii) Valence electrons are the
but there are more electrons in the outermost
empty spaces electron shell. 1
between the (b) (i) Isotopes are atoms with the
particles. same proton number but
F or ces of The forces The forces of The forces 2 different nucleon numbers.
attraction of attraction attraction between of attraction
between the the particles are between the 3
particles are weaker than in a particles are very
(ii) 168O and 188O are isotopes of
oxygen. 2
strong. solid but stronger weak. (iii) Six uses of isotopes:
than in a gas. 1 Medicine
K in etic energy The kinetic The kinetic energy The kinetic energy 2 (a) Cobalt-60 is used to kill
energy of the of the particles is of the particles is 2 malignant cancer cells in
particles is low. high on average. very high. radiotherapy.
C om pressibility Low Low High (b) Some medicine, surgical
gloves, bandages, plastic
(vi) The experiment is repeated hypodermic syringes which
(b) Apparatus Boiling tube, retort cannot be sterilised by boiling
F stand and clamp, tripod stand, by replacing substance X with are sterilised using gamma
Bunsen burner, wire gauze, substance Y. 6 radiation. 2
O thermometer (0 – 110 °C), Tabulation of results 2 Agriculture
R 500 cm3 beaker, 250 cm3 Substance X (a) Radioactive 14CO2 is used
M conical flask, test tube holder and to trace the path of carbon
stopwatch. 1 Time 0 30 60 90 120 … during photosynthesis.
(s)
4 Material X and Y, water 1 (b) Radioactive 32PO43– ions are
Procedure Temp used to determine the rate
(°C) of absorption of phosphorus
Substance Y by the plant. 2
3 Industry
Time 0 30 60 90 120 … (a) Beta radiation is used to
(s) control the thickness of
paper, plastic, metals and
Temp rubber made in industry.
(°C)
(b) Radioisotope is used to
CHAPTER 2 1 detect leaks in pipes carrying
A graph of temperature
against time is plotted for both gas. 2
substances. The melting point of
the substance is obtained from 4 Archaeology
the region where the temperature
(i) Three spatulas of X powder remains constant at T. 1 The activity of the carbon-14 still
If the melting point of the
are put into a boiling tube. substance is 65 °C, then the remaining in an archaeological
substance is naphthol.
(ii) A 500 cm3 beaker is filled If its melting point is 80 °C, specimen can be used to
then the substance is
with water until it is atbripooudt –34 naphthalene. 1 estimate the age of the
full and placed on a
specimen. 2
stand. 5 Food preservation
(iii) The boiling tube containing (a) Fungus, bacteria and larvae
X powder is then clamped in that cause the rotting of food
the water bath with the level can be killed by irradiating
of X powder below the water the food with radiation.
level. (b) Budding in potatoes and
(iv) The water bath is heated onions is slowed down by
until it reaches a temperature irradiation, thus extending
of about 55 °C. Then the their shelf-life. 2
water is heated with low 6 Electricity generation
flame. The nuclear energy released
(v) The stopwatch is started when uranium-235 decays
and the temperature of the 1 spontaneously is used to heat
water into steam which then
substance X is recorded 2 (a) (i) Proton number is the
every 30 seconds. The result number of protons in the drives turbines of the generator to
is then tabulated. nucleus of an atom. 1 produce electricity. 2
Answers 540
Experiments Initial 30 60 90 120 150 180 210 1 (b) Let the number of carbon atoms
1 (a) Time (s) that has the same mass as one
80.0 80.0 82.0 85.0 95.0 3 Mo atom be n.
Temp (°C) 70.0 78.0 80.0 12n = 96
3 n = —9——6 = 8
(b)
Materials Pure naphthalene, 12
a mixture of naphthalene with
(c) some acetamide and water. 3 (c) Let relative atomic mass of
(d) Procedure phosphorus = m
3 (i) 3 spatulas of naphthalene Mass of five aluminium atoms F
= mass of six lithium atoms + O
(d) 80 °C 3 powder are put into a boiling mass of three phosphorus R
tube. atoms M
(ii) A 500 cm3 beaker is filled with (5 27) = (6 7) + 3m 4
water until it is about —43 full 3m = 135 – 42
(e) A mixture of solid and liquid and is then placed on a tripod m = —9——3 = 31
stand.
naphthalene. 3 (iii) The boiling tube containing 3
naphthalene is then clamped
(f) The heat energy absorbed is in the water bath with the (d) (i) Relative atomic mass of Th
level of naphthalene powder = (6 7) + (2 39) +
used to overcome the forces below the water level. (2 56) = 232
(iv) The water bath is heated until
of attraction between the it reaches a temperature of (ii) Assume that the mass of n
about 65°C. Then the water is W atoms
naphthalene molecules. Hence, heated with a low flame.
(v) The stopwatch is started = mass of two X atoms +
the temperature remains constant and the temperature of the mass of one Y atom +
naphthalene is recorded at mass of one Z atom
during the melting process. 3 30-second intervals until the
temperature reaches 90 °C. 7n = (2 39) + 56 + 195
(g) The results are tabulated. n = 47 atoms CHAPTER 2 & 3
(vi) The experiment is repeated 2 (a) Relative molecular mass of
3 by replacing the pure C17H35COONa
naphthalene with a mixture = 17(12) + 35(1) + 12 + 2(16)
2 (a) Aim To show that the presence of naphthalene with + 23
acetamide. 3 = 204 + 35 +12 +32 +23 = 306
of acetamide as an impurity will (b) Relative formula mass of
(e) Tabulation of results Cu(NH3)4SO4
lower the melting point of Pure naphthalene = 64 + 4(14 +3) + 32 + 4(16)
= 64 + 68 +32 +64 = 228
Time (min) 0 –12– 1 1 –12–
Temp (°C) There are four ammonia,
NH3 molecules
3 Assume the relative atomic mass of
the element X is a.
Relative molecular mass of X2B4O7
= 202
2a + 4(11) + 7(16) = 202
a = 23
The relative atomic mass of X is 23.
Thus, X is sodium atom.
2 2–21– 3 3 –12– 4 4 –21– 5
naphthalene. 3
(b) Manipulated variable Pure Mixture of naphthalene and acetamide
naphthalene and a mixture of
naphthalene with some acetamide. Time (min) 0 –12– 1 1 –21– 2 2–21– 3 3 –12– 4 4 –21– 5
Responding variable Melting
point of substance Temp (°C) 3
Constant variable Atmospheric
pressure, constant stirring during
heating. 3 3 Chemical Formulae and Equations
(c) Apparatus 500 cm3 beaker, two Self Assess 3.1
1 (a) The relative atomic mass of Pt atom = 5 relative atomic mass of K atom
boiling tubes, thermometer, stop-
= 5 39 = 195
watch, retort stand and clamp,
tripod stand, wire gauze.
541 Answers
Self Assess 3.2 (b) 1 mol of C10H14N2 1 mol of C6H12O6 contains
= 10(12) + 14 + 2(14) g 6 1023 molecules.
1 ( a) —61— 6 1023 = 162 g 0.2 mol of C6H12O6 contains
= 1 1023 copper atoms 0.2 6 1023 molecules
4.05 g of C10H14N2 = —41—.60—25 mol = 1.2 1023 molecules
(b) 0.0625 6 1023 = 5 (a) The molecule consist of 10
3.75 1022 water molecules = 0.025 mol carbon atoms, 16 hydrogen atoms
(c) 1 mol of (NH4)3PO4 and one oxygen atom. Hence its
(c) 1.3 6 1023 = molecular formula is C10H16O.
7.8 1023 sodium ions = 3(14 + 4) + 31 + 4(16) Thus, the mass of 1 mol of
= 149 g C10H16O = 10(12) + 16 + 16 g
2 (a) 0.012 mol of C2H6 contains
0.012 6 1023 molecules. 1 .49 g of (NH4)3PO4 = —11—.44—99 mol = 152 g
(b) 1 mol of C10H16O = 152 g
One molecule of C2H6 has eight = 0.01 mol
atoms (two carbon and six (d) 1 mol of C2H5OH 0.02 mol of C10H16O
hydrogen atoms). = 0.02 152 g = 3.04 g
= 2(12) + 6 + 16 g (c) 1 mol of C10H16O =152 g
Therefore, the number of atoms = 46 g Hence, 7.6 g of C10H16O
= 8 0.012 6 1023 atoms = —17—5.62– mol
= 5.76 1022 atoms 2 .3 g of C2H5OH = —24—.63 mol
(b) 1.1 mol of SO3 contains = 0.05 mol
1.1 6 1023 molecules. = 0.05 mol 1 mol of C10H16O contains
One molecule of SO3 has four 3 (a) 1 mol contains 6 1023 atoms. 6 1023 molecules.
atoms (one sulphur and three
oxygen atoms). 3 1023 titanium atoms
= —3————1—0——23——a—t—o—m—— 1 mol
6 1023 atom 0.05 mol of C10H16O contains
= 0.5 mol 0.05 6 1023
= 3 1022 molecules.
Therefore, the number of atoms 1 mol of Ti = 48 g (d) 7.5 1022 molecules
0.5 mol of Ti = 0.5 48 g = —7—.5—————1—0—2—2 1 mol
F = 4 1.1 6 1023 atoms 6 1023
O = 2.64 1024 atoms = 24 g = 0.125 mol
R 3 (a) 1 mol of sodium ions contains (b) 1.2 1024 of argon atoms contain
M 6 1023 ions.
= —1—6.—2———1—01—02—3—24 mol
Therefore, 6 1022 sodium ions = 2 mol
4 = —66————11—00—2—223——ioi—on—n—ss— 1 mol-ion 1 mol of argon = 40 g 1 mol of C10H16O = 152 g
2 mol of argon = 2 40 g 0.125 mol of C10H16O
= 0.125 152 g = 19 g
= 0.1 mol-ion = 80 g
(b) 1 mol of H2S contains 6 1023 (c) 7.5 1022 molecules of Self Assess 3.4
molecules C12H16O14 1 1 mol of gas occupies a volume of
= —7—.6—5———1—10—02—3—22 mol
Therefore 1.8 1024 H2S = 0.125 mol 24 dm3 at room temperature.
= 1—.—8———1—0—2—4 —m——o—le—c—u—l—e–s 1 mol- 1 mol of C12H16O14 0.55 mol of gas occupies a volume of
6 1023 molecules molecule = 12(12) + 16 + 14(16) g 0.55 24 dm3 = 13.2 dm3
2 1 mol of gas occupies a volume of
= 3 mol-molecules
CHAPTER 3 = 384 g 22 400 cm3 at s.t.p.
Self Assess 3.3 0.125 mol of C12H16O14 The number of mol of gas in 672 cm3
1 (a) 1 mol of He = 4 g = 0.125 384 g
= 48 g is —226—74—20—0 mol = 0.03 mol
1.25 mol of He = 1.25 4 g 4 (a) 1 mol of S = 32 g 3 1 mol of C2H4 = 28 g
=5g 1 .4 g of C2H4 = —12–.—84 mol = 0.05 mol
4 g of S = —34—2 mol
(b) 1 mol of Co = 59 g 1 mol of gas occupies a volume of
= 0.125 mol 24 dm3 at room temperature
– 52– mol of Co = –25– 59 g 1 mol of S contains 6 1023 0.05 mol of gas occupies a volume of
atoms. 0.05 24 dm3 = 1.2 dm3
= 23.6 g 0.125 mol of S contains 4 (a) 1 mol of gas occupies a volume
(c) 1 mol of CuSO4.5H2O 0.125 6 1023 atoms
= 7.5 1022 atoms of 22.4 dm3 at s.t.p.
= 64 + 32 + 4(16) + 5(18) g (b) 1 mol of Cd = 112 g The number of mol of gas in
= 250 g
0.15 mol of CuSO4.5H2O 2 .24 g of Cd = —21—.12—24 mol 1 6.8 dm3 of gas is —21–62–..—84 mol
= 0.15 250 g
= 37.5 g = 0.75 mol
1 mol of CH4 = 16 g
(d) 1 mol of KMnO4 = 0.02 mol 0.75 mol of CH4 = 0.75 16 g
= 39 + 55 + 4(16) g 1 mol of Cd contains 6 1023 = 12 g
= 158 g atoms. (b) 1 mol of gas occupies a volume
0.05 mol of KMnO4 0.02 mol of Cd contains 0.02
= 0.05 158 g 6 1023 atoms of 22.4 dm3 at s.t.p.
= 7.9 g = 1.2 1022 atoms The number of moles of gas in
6720 cm3 of gas is —26—27—42—00—0 mol
2 (a) 1 mol of Fe = 56 g (c) 1 mol of C6H12O6 = 180 g
2.8 g of Fe = —25—.68— 1 mol 3 6 g of C6H12O6 = —1—386—0 mol
= 0.05 mol = 0.2 mol = 0.3 mol
Answers 542
1 mol of CO = 28 g 4 Assume that the relative atomic mass Relative molecular mass of gas is
0.3 mol of CO = 0.3 28 g of V is a. [12 + 3]n = 30
n = 2
= 8.4 g Element V O Therefore, its molecular formula
10.2 g 8g is C2H6.
5 (a) 3 .6 dm3 of gas = —32–.4—6 mol Mass —8— = 0.5
= 0.15 mol —1—0—a—.2— Self Assess 3.6
Number of 16
The number of molecules present moles 1 (a) 2Na(s) + 2H2O(l) →
is 0.15 6 1023 25 2NaOH(aq) + H2(g)
= 9 1022 molecules Simplest
ratio (b) Zn(s) + 2HCl(aq) →
(b) 1 200 cm3 of gas = —21—42—0—00—00 mol
= 0.05 mol 1 —— 00——a..——5 2 = —52— ZnCl2(aq) + H2(g)
The number of molecules present (c) CuCO3(s) + 2HNO3(aq) →
is 0.05 6 1023 a = —12—0—.—2–––0––.–5—5 = 51
= 3 1022 molecules Cu(NO3)2(aq) + CO2(g) + H2O(l)
5 Element N H (d) 2HCl(aq) + Na2S2O3(aq) →
6 9 1021 molecules of CO 12.5 %
= —9————1——0—2—1 = 0.015 mol Mass 87.5 % 2NaCl(aq) + SO2(g) + S(s) +
6 1023 —1—2—1—.5— H2O(l)
(e) 2Pb(NO3)2(s) heat→
The volume occupied by 0.015 mol = 12.5
of gas is 0.015 22.4 dm3 Number of —8—1—74—.5— 2PbO(s) + 4NO2(g) + O2(g)
= 0.336 dm3 at s.t.p. moles —61—2.—2—.55— 2 (a) 2SO2(g) + O2(g) → 2SO3(g)
(b) 2KOH(aq) + H2SO4(aq) →
= 6.25 =2
K2SO4(aq) + 2H2O(l)
Self Assess 3.5 Simplest —66——..22—55— (c) 2C2H6(g) + 7O2(g) → F
1 (a) AgNO3 ratio O
=1 4CO2(g) + 6H2O(l) R
(b) Na2S2O3 (d) Zn(s) + CuSO4(aq) → M
(c) (NH4)3PO4 (a) Empirical formula is NH2. 4
(d) Ca(OH)2 (b) Let its molecular formula be (NH2)n Cu(s) + ZnSO4(aq)
(e) MgCO3 (e) ZnCO3(s) hea→t ZnO(s) + CO2(g)
(f) Zn3P2 (14 + 2)n = 32
(g) Fe(OH)3 16n = 32 (f) PbO2(s) + 2H2(g) →
(h) Al2O3 n=2 Pb(s) + 2H2O(l)
(i) CrCl3
(j) CuSO4 3 (a) Fe(s) + 2HCl(aq) →
(k) NiCl
(l) Mg3N2 Its molecular formula is N2H4. FeCl2(aq) + H2(g)
2 Percentage by weight of hydrogen (b) (i) 1 mol of Fe (56 g) produces
= (100 – 87.5)% = 12.5 %
6 Element Fe O 1 mol of FeCl2 (127 g)
Hence, 2.8 g of Fe produce
Mass x g 5.04 g — 25—–.6—8 127 g = 6.35 g of FeCl2
Number of ——5—x6—— 5.04 (ii) 1 mol of Fe (56 g) produces
moles ——1—6——
1 mol of H2 (24 dm3)
Element Si H = 0.315 Hence, 2.8 g of Fe produce
Percentage 87.5 % 12.5 % Simplest 2 3 —25—–.—6824 dm3 CHAPTER 3
mass ratio
Number of —8——7—.5— —1—2—.—5— —0——.—35—x—61—— 5— = —32— =1.2 dm3 of H2.
moles 4 (a) 1 mol of CaC2(40 + 12 + 12) g
28 1
produces 1 mol of C2H2 (24
= 3.125 = 12.5 x = 11.76 g dm3) at room temperature and
Simplest ——3—.—1—2—5— ——1—2——.5— 7 Element C H pressure. Hence, 4.8 g of CaC2
ratio 3.125 produce 4—6—.48— 24 dm3 = 1.8 dm3
3.125
=1 Percentage 80 % 20 %
=4 by weight
Its empirical formula is SiH4. Number of —8—0— = 6.67 —2—0— = 20 of C2H2 gas.
3 Mass of oxygen that combines with tin moles 12 1 (b) 1 mol of CaC2(40 + 12 + 12) g
produces 1 mol of Ca(OH)2
is (7.55 – 5.95) g = 1.60 g Simplest 6.67 (40 + 17 + 17) g.
ratio
Element Sn O —6—.—6—7— 20 Hence, 4.8 g of CaC2 produce
1.6 g —6—.—6—7— —46—–.—48 74 g
Mass 5.95 g =1
1.6 =3
———
Number of 5.95 (a) Its empirical formula is CH3. = 5.55 g of Ca(OH)2
————— 16 (b) 1 mol of gas has mass of 1 mol of CH4(16 g) produces
moles 119 5 (a)
= 0.1 —42—2.–4–.48— 6 g = 30 g
= 0.05 Therefore, its relative molecular 3 mol (3 24 dm3) of H2.
——0—.—1— mass is 30. Hence, 60 dm3 of H2 is produced
Simplest —0——.0——5 0.05 (c) Assume its molecular formula is from
ratio 0.05 (CH3)n.
=2 = ———6—0——d—m——3——H—2—— 16 g
=1 3 24 dm3 H2
Its empirical formula is SnO2. = 13.33 g of CH4
543 Answers
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