SCIENCE FOR 5 PART 2

Chapter 5 Carbon Compounds

Activity 5.10 21st Century Skills

To prepare a review about a visit to a palm oil processing factory or to the • TPS, ISS, ICS
Malaysian Palm Oil Board (MPOB) • Inquiry-based activity

Instructions

1. Pay a visit to a palm oil processing factory or to the Malaysian Palm Oil Board (MPOB).
2. Gather and record information on the sequence of the industrial extraction process of palm

oil in your notebook.
3. Based on the information gathered, review the industrial extraction process of palm oil.

Components of Palm Oil

Palm oil is made up of two parts, namely glycerol and various types of fatty acids
(Figure 5.24).

Palm oil

Glycerol Fatty acids

Figure 5.24 Components of palm oil

Palm oil is made up of saturated fatty acids such as palmitic acid and stearic acid,
as well as unsaturated fatty acids such as oleic acid and linoleic acid.

Composition of Palm Oil and Other Vegetable Oils

The composition of palm oil and other vegetable oils is shown in Table 5.3.

Activity 5.11 21st Century Skills

To study the differences in composition such as glycerol and fatty acid in palm ICS
oil and other vegetable oils

Instructions

1. Carry out this activity in groups.
2. Conduct online searches through the Internet to gather information on the differences in

composition such as the glycerol and fatty acid content in palm oil and other vegetable oils.
3. Discuss the information gathered.
4. Present your findings using a graphic organiser.

5.5.3 5.5.4 5.5.5 163

Table 5.3 Comparing and contrasting the composition of palm oil with other vegetable oils
Weight percentage of fatty acids (%)

Ratio of Saturated Mono Poly
unsaturated
unsaturated unsaturated
fats/
Oil or fat saturated

fats Capric Lauric Myristic Palmitic Stearic Oleic Linoleic Alpha
acid acid acid acid acid acid acid linoleic

acid

Coconut 0.1 6 47 18 9 3 6 2-
oil

Corn oil 6.7 - - - 11 2 28 58 1

Olive oil 4.6 - - - 13 3 71 10 1

Palm oil 1.0 - - 1 45 4 40 10 -

Palm 0.2 4 48 16 83 15 2-
kernel oil 4.0
6.6 - - - 11 2 48 32 -
Peanut 5.7
oil --- 94 41 45 -

Sesame - - - 11 4 24 54 7
oil

Soya
bean oil

Source: MPOB, UCCS, NCBI and Oil Palm Knowledge Base

164 5.5.5

Chapter 5 Carbon Compounds

The Chemical Properties of Palm Oil

The chemical properties of palm oil are explained in the following aspects:

(a) Oxidation
Oxidation of palm oil occurs when its oil molecules combine with oxygen in the
air or from other reactants. The oxidation of palm oil produces free radicals and
compounds which are harmful to human health.

(b) Hydrolysis
Hydrolysis occurs in palm oil when palm oil molecules react with water. In the
hydrolysis process, the reaction between palm oil and water produces glycerol and
fatty acids.

(c) Esterification
Esterification of palm oil occurs when its fatty acid molecules react with alcohol to
produce ester (methyl ester), that is palm oil biodiesel.

Emulsification Process of Palm Oil Video

The emulsification of palm oil is a process where palm Emulsification
oil is broken into smaller droplets. This increases the process of oil
total surface area of the palm oil. How does the increase such as palm oil
in total surface area of palm oil influence the rate of http://buku-teks.
digestion of palm oil? The emulsification of palm oil by com/sc5165a
bile juice is shown in the video on the right.

Nutritional Content of Palm Oil My Malaysia

The nutritional content of palm oil are as follows: Scientists from the Malaysian
Palm Oil Board have
(a) Fats conducted various research
Palm oil is a balanced oil with the same amount of on the nutritional content of
saturated fats and unsaturated fats (Table 5.3). palm oil.
http://buku-teks.com/sc5165b
(b) Vitamins
Palm oil is a rich source of vitamin E and vitamin A.

5.5.6 5.5.7 5.5.8 165

(c) Antioxidants
Palm oil contains antioxidants such as carotene and vitamin E which slow down or
stop the oxidation process.

(d) Substances in palm oil which constitute less than 1%
Among the substances contained in palm oil include sterol, phosphatides, triterpene
and aliphatic alcohols. These substances add nutritional value, stability and facilitate
the filtration of oil.

Use of Palm Oil in Healthcare and Food

Besides a balanced content of saturated fats and unsaturated fats, palm oil contains
many nutrients suitable for use in various types of food such as cooking oil, vegetable
oil, margarine and chocolate.

Palm oil is also used to make non-food substances (Photograph 5.7).

Photograph 5.7 Examples of palm oil-based products

Activity 5.12 21st Century Skills

To study the use of palm oil-based products as well as their effects • ICS
on human health • Discussion

Instructions

1. Carry out this activity in groups.

2. Conduct online searches through the Internet to gather information on the uses of palm oil-

based products in:

(a) medicine (b) plastic surgery (c) cosmetics (d) prosthetics

3. Discuss the information gathered. Give reasons why the use of palm oil-based products and

their effects on human health need to be justified.

4. Present your findings using a graphic organiser or multimedia presentation.

166 5.5.8 5.5.9

Soap Production Chapter 5 Carbon Compounds

Soap is a fatty acid salt normally produced through Entrepreneurship
the reaction between palm oil and concentrated alkali
(concentrated sodium hydroxide or concentrated A soap business can be carried
potassium hydroxide) as in the following out from home. The substances
word equation: used are natural substances,
natural fruit extracts and
Oil + Alkali Fatty acid salt (soap) + Glycerol fragrances from approved
aromatic resources for making
organic soap.

Experiment 5.1

Aim: To produce soap through saponification

Problem statement: How is soap produced?

Materials: Palm oil, 5 mol dm–3 concentrated sodium hydroxide solution,
distilled water, sodium chloride, filter paper, red litmus paper and
blue litmus paper

Apparatus: Beaker, measuring cylinder, glass rod, Bunsen burner, tripod stand,
wire gauze, filter funnel, retort stand, spatula, test tube and conical flask

Procedure:

50 cm3 of 5 mol dm–3 Distilled water Sodium chloride Filter
sodium hydroxide solution paper

Soap

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Heat Heat

10 cm3 of palm oil Filtrate

(a) (b) (c) (d) (e) (f)

Figure 5.25 Process of soap production

1. Measure and pour 10 cm3 of palm oil into a clean beaker using a measuring cylinder.
2. Measure and pour 50 cm3 of 5 mol dm–3 concentrated sodium hydroxide solution into the

beaker (Figure 5.25(a)). Observe and record the changes of the mixture in the beaker.
3. Stir and boil the mixture in the beaker for 5 minutes (Figure 5.25(b)). Observe and record

the changes to the mixture in the beaker after heating.

5.5.10 167

4. Stop heating the mixture. Measure and pour 50 cm3 of distilled water as well as three
spatula full of sodium chloride into the solution in the beaker (Figure 5.25(c)). Observe and
record changes to the mixture in the beaker.

5. Stir and boil the mixture in the beaker again for 5 minutes (Figure 5.25(d)).
6. Filter the mixture in the beaker (Figure 5.25(e)).
7. Rinse the residue with distilled water and dry it.
8. Add a little water to the dried residue in a test tube and shake it. Observe and record the

changes when the residue is mixed with water and shaken, and when you touch it with your
fingers (Figure 5.25 (f)).
9. Test the mixture of the residue and water with red and blue litmus papers. Observe and
record the change in colour, if any, to the red and blue litmus papers.

Observations:

Record your observations for procedures 2, 3, 4, 8 and 9.

Conclusion:

What is the conclusion for this experiment?

Molecular Components of Soap and Cleansing Action of Soap

Molecular Components of Soap

Soap molecules are made up of two parts (Figure 5.26), namely:
(a) the ‘head’ or ‘hydrophilic’ part which can dissolve in water and is made up of an

ionic group.
(b) the ‘tail’ or ‘hydrophobic’ part which cannot dissolve in water but can dissolve in

oil or grease. This part is made up of a hydrocarbon chain.

Head Tail

Hydrophilic part Hydrophobic part

(can dissolve in water) (can dissolve in grease or oil)

Figure 5.26 Molecular structure of soap
Why is soap able to dissolve in water as well as in oil or grease?

168 5.5.10 5.5.11

Cleansing Action of Soap Soap Chapter 5 Carbon Compounds

The cleansing action of soap is as follows: Surface of Water
cloth
(a) when soap dissolves in water, the Greasy
surface tension of the water is dirt
reduced. Therefore, the surface of (a)
cloth becomes completely wet with
soap water. Water

(b) the hydrophobic part of the soap Surface of
molecules will dissolve and attach cloth
to the greasy dirt on the cloth
surface while the hydrophilic part (b)
will dissolve in water
(Figures 5.27(a) and (b)). Greasy Water
droplets
(c) scrubbing and brushing the cloth surrounded
will dislodge the greasy dirt from by soap
the cloth surface to form greasy molecules
droplets that are surrounded by
soap molecules and suspended in Surface of (c)
soapy water (Figure 5.27(c)). cloth

(d) soap bubbles produced by soapy
water trap greasy droplets in the
soapy water. When the soapy
water and bubbles are removed
during rinsing, the greasy dirt will
also be removed as well. In this
way, soap removes greasy dirt and
cleans the cloth.

Figure 5.27 Cleansing action of soap

Sustainable Management and its Importance in the
Palm Oil Industry

The scope of sustainable management and its importance in the palm oil
industry include:

(a) Land use
Replanting is carried out to optimise land use.

(b) Wastewater
Palm oil mill effluent (POME) (Photograph 5.8) produced from sterilisation
processes are made into organic fertilisers and biogas energy substances.

5.5.11 5.5.12 169

(c) Air quality
The quality of air improves
when carbon dioxide is
absorbed and oxygen is
released by oil palm trees
during photosynthesis.

(d) Oil palm waste
Sustainable management of
oil palm industry normally
practises zero waste concept
by converting oil palm waste
into various types of useful
products (Figure 5.28).

Photograph 5.8 POME from palm oil mill

Fronds made into fertilisers Tree trunks as Empty fruit bunches turned
wood replacement into compost

Types of biomass (Oil palm waste)

Shells are burnt Pulp fibre is made into POME turned into
to boil water carpets and textile biogas and fertilisers

Figure 5.28 Applications of the zero waste concept in the oil palm industry

170 5.5.12

Chapter 5 Carbon Compounds

Activity 5.13 21st Century Skills

To conduct a debate or forum on the efficient management of the palm oil • ICS, ISS, TPS
industry to counter the negative perceptions of Western countries on local • Debate
palm oil

Instructions

1. Carry out this activity in groups.
2. Gather information from the Internet, print media and other electronic media on the

negative perceptions of Western countries on local palm oil.

Example of negative perception
The oil palm industry has been linked to worldwide deforestation. This happens when
forests are burnt to provide agricultural land for planting oil palm trees.

3. Discuss and generate ideas on sustainable management to counter the negative perceptions
of Western countries on local palm oil. The scope of discussion should include:
(a) land use
(b) wastewater
(c) air quality
(d) oil palm waste

4. Conduct a debate or forum to discuss this topic.

Formative Practice 5.5

1. Name the oil extracted from the following parts of the oil palm fruit:
(a) pulp
(b) kernel

2. Why are the oil palm fruits steamed before oil is extracted?

3. What are the reactants that react with palm oil in the following processes?
(a) Hydrolysis
(b) Esterification

4. Name two antioxidants found in palm oil.

5.5.12 171

172 Summary

Alkane Saturated
hydrocarbons

Hydrocarbon Organic carbon Inorganic carbon Oil palm fruit
compounds compounds compounds

Alkene Unsaturated Its importance
hydrocarbons Carbon cycle

Pulp Kernel

Glucose or starch fermentation Alcohol

Palm oil Palm kernel oil

Physical properties of alcohol: Chemical properties Carbon Compounds Chemical Contents: Products:
• colour of alcohol: Fats properties: • unsaturated • soap
• odour • combustion • oxidation • medicine
• physical condition at room • esterification • hydrolysis fats • plastic
• esterification • saturated fats
temperature • vitamins surgery
• volatility • antioxidants • cosmetics
• boiling point • prosthetics

Saturated fats Unsaturated fats

Uses of alcohol:
• fuel
• medicine
• cosmetics
• industry

Excessive alcohol consumption

Alcohol addiction

Chapter 5 Carbon Compounds

Self-Reflection

After studying this chapter, you are able to:

5.1 Introduction to Carbon 5.5 Palm Oil
Compounds Describe the structure of oil
Identify carbon compounds palm fruit.
in nature. Identify the quantity of oil from pulp
Explain the importance of and kernel.
carbon cycle. Explain in order the process of palm
oil extraction in industry.
5.2 Hydrocarbons Describe components of palm oil.
Describe hydrocarbon compounds Compare and contrast the
and explain how carbon compounds composition of palm oil with other
are obtained from natural sources. vegetable oils.
Name members of the homologous State the chemical properties of
series of alkanes and alkenes from palm oil.
carbon 1 to carbon 6. Explain the emulsification process of
Communicate about alternative palm oil.
energy sources and renewable energy List the nutritional content of
in daily life. palm oil.
Justify the use of palm oil in
5.3 Alcohol healthcare and food.
Describe the preparation of alcohol. Carry out an experiment to produce
Identify the physical properties and soap through saponification.
chemical properties of alcohol. Communicate about the cleansing
Communicate about the uses of action of soap.
alcohol in daily life. Generate ideas on sustainable
Communicate about the effects of management and their importance in
excessive alcohol consumption. the palm oil industry.

5.4 Fats
State the content of fats and its
sources.
Compare and contrast between
saturated and unsaturated fats.
Explain with examples, the effects of
eating food containing excess fat
on health.

173

Summative Practice 5 Quiz
http://buku-
Answer the following questions: teks.com/
1. Figure 1 shows an experiment to study the preparation sc5174
of a type of carbon compound.

Test tube

Conical flask

Sugar solution Limewater
+ yeast

Figure 1

(a) Name the process in Figure 1.
(b) What type of carbon compound is prepared?
(c) State your observation of the limewater.
(d) State the inference for your answer in 1(c).

2. Figure 2 shows a cross section of an artery blocked by substance P which causes
the lumen of the artery to become narrow and disrupts or blocks blood flow.

Substance P

Lumen

Figure 2
(a) Name the condition.
(b) Name substance P.
(c) What class of food causes blocked arteries?
(d) Suggest two ways to avoid blocked arteries.

174

Chapter 5 Carbon Compounds

3. Figure 3 shows a cross section of an oil palm fruit.

X:
Y:

Z:

Figure 3

(a) Name the parts labelled X, Y and Z.
(b) Name the type of oil extracted from parts X and Y.
(c) Complete the flow chart for the extraction process of palm oil.

(i) Threshing (ii)

Purification (iii) Extraction

(d) Give three reasons why palm oil is suitable as cooking oil.

Enrichment Practice

4. Assume that you are tasked to build a new palm oil mill which operates based on
zero waste concept.

Figure 4
Build a graphic organiser to show how zero waste concept is applied in the oil palm
industry such as the conversion of oil palm waste into oil palm biomass.

175

6CHAPTER ELECTROCHEMISTRY

State three uses of electrolysis.

Name the process used in the treatment
of wastewater by applying electrolysis.

Give one example of a fruit and one
example of a plant part which can
be used to build a chemical cell that
produces electrical energy.

Let’s study

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176

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Charging the electric car battery Lithium-ion batteries in an electric car

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177

6.1 Electrolytic Cell

Electrochemistry is a study in chemistry of the relationship between electrical and
chemical phenomena like those occurring in two types of electrochemical cells
as follows:

(a) Electrolytic cell
In an electrolytic cell, electric current flows through an electrolyte to produce
a chemical reaction. Electrical energy is converted to chemical energy through
electrolysis.

(b) Chemical cell (voltaic cell or galvanic cell)
In a chemical cell, chemical changes that occur in the cell produce an electric
current. Chemical energy is converted to electrical energy in the cell.

Electrolysis Test tube

In Form 2, you studied about Carbon Distilled water
electrolysis that is used to determine electrodes + dilute
the composition of elements in water hydrochloric
molecules using an electrolytic cell acid
(Figure 6.1).
+–
Electrolysis is the decomposition
of a compound in the molten or Switch
aqueous state into its constituent
elements when electric current flows Figure 6.1 Electrolytic cell
through it. What are the decomposed
compound and constituent elements Rheostat Battery e-
produced in the electrolysis process Anode (+) +–
(Figure 6.1)? A
Cation e-
An electrolytic cell is made up of: Electrolyte
• an electrical source such as battery Cathode (–)
• an anode which is the electrode
+_ +
connected to the positive terminal
of an electrical source _ _ Anion
• a cathode which is the electrode _+
connected to the negative terminal
of an electrical source
• an electrolyte which contains positive
ions (cations) and negative ions
(anions) (Figure 6.2)

++

Figure 6.2 Electrolytic cell

178 6.1.1

Chapter 6 Electrochemistry

Electrical Source

The function of the electrical source in an electrolytic cell is to produce electric
current to carry out electrolysis. Electrolysis cannot take place if there is no electric
current flowing through the electrolyte.

Electrode

Electrode is the electric conductor that is connected to the battery and enables electric
current to enter or leave the electrolyte during electrolysis. The electrode connected to
the positive terminal of the electrical source is known as the anode while the electrode
connected to the negative terminal of the electrical source is known as the cathode.

Electrolyte

Substances in the molten or aqueous state which allow electric current to flow through
them and undergo chemical changes are known as electrolytes. Substances which
do not allow electric current to flow through them in the molten or aqueous state are
known as non-electrolytes.

Table 6.1 Examples of electrolyte and non-electrolyte

Examples of electrolyte Examples of non-electrolyte

• Molten lead(II) bromide, PbBr2 • Naphthalene, C10H8
• Molten sodium chloride, NaCl • Acetamide, CH3CONH2
• Glucose solution, C6H12O6
• Sodium hydroxide solution, NaOH • Ethanol, C2H5OH

• Copper(II) sulphate solution, CuSO4

Electrolytes are ionic compounds in the molten or aqueous state which consist

of positive ions, cations and negative ions, anions. For example, sodium chloride is
an electrolyte which is an ionic compound made up of sodium ions, Na+ (positively
charged ions) and chloride ions, Cl– (negatively charged ions).

NaCl Na+ + Cl–

Activity 6.1 21st Century Skills

To draw and label the structures of an electrolytic cell • TPS

Instructions

1. Carry out this activity individually.
2. Draw and label the electrolytic cell in Figure 6.1. The parts that need to be labelled include:

(a) anode
(b) cathode
(c) electrolyte
3. Present the drawing of the labelled electrolytic cell to the class.

6.1.1 179

Electrolysis Process

During the electrolysis process,
• positively charged ions (cations) move to the cathode (negative electrode)
• negatively charged ions (anions) move to the anode (positive electrode)

For example, during the electrolysis of molten lead(II) bromide, PbBr2, positively
charged lead(II) ions, Pb2+, move to the negatively charged cathode while negatively
charged bromide ions, Br–, move to the positively charged anode (Figure 6.3).

+Batter–y Positively Negatively

charged anode charged cathode

Anode Cathode

Molten Br– Pb2+ Pb2+
lead(II) bromide, Br– Br– Pb2+
PbBr2 Br–
Br– Lead(II) ion, Pb2+
Heat
Bromide Br–
ion, Br–

Figure 6.3 Movement of ions towards electrodes during
the electrolysis of molten lead(II) bromide, PbBr2

Electrolytes in the solid state cannot conduct electricity because there are no
free-moving ions to conduct the electricity.

Experiment 6.1

Aim: To study the electrolysis of ionic compounds in solid, molten and
aqueous states

Problem statement: Can ionic compounds in solid, molten and aqueous states be
electrolysed?

Hypotheses: 1. Ionic compounds in molten and aqueous states can be electrolysed.
2. Ionic compounds in solid state cannot be electrolysed.

Variables: (a) manipulated : State of ionic compound, namely solid, molten
or aqueous
Materials:
Apparatus: (b) responding : Condition of light bulb
180 (c) constant : Type of electrode

Solid lead(II) bromide, PbBr2 and 0.1 mol dm–3 copper(II) sulphate
solution, CuSO4

Battery, carbon electrodes, connecting wires with crocodile clips,
crucible, tripod stand, pipe clay triangle, Bunsen burner, switch, beaker,
light bulb, electrolytic cell, spatula and test tubes

6.1.1 6.1.2

Chapter 6 Electrochemistry

Procedure:

A Electrolysis of ionic compound in solid and molten states

Teacher’s demonstration (carried out in a fume chamber) CAUTION!
1. Put solid lead(II) bromide powder, PbBr2, into a dry
Bromine gas is poisonous. Do
crucible until it is half-full.

2. Place the crucible on a pipe clay triangle atop a tripod not inhale the bromine gas.

stand (Figure 6.4).

3. Complete the circuit by connecting the carbon electrodes, switch, battery and light bulb

with connecting wires and crocodile clips.

4. Turn on the switch. Observe and record the changes that happen to the light bulb.

5. Heat the solid lead(II) bromide, PbBr2, until it melts (Figure 6.5).
6. Repeat steps 3 and 4.

Switch Battery Switch +Batter–y
+–

Crocodile clip Light bulb Crocodile clip Light bulb

Crucible Carbon electrodes Crucible Carbon electrodes
Solid lead(II) bromide, Molten lead(II) bromide,
Pipe clay PbBr2 Pipe clay PbBr2
triangle triangle
Heat

Figure 6.4 Electrolysis of solid Figure 6.5 Electrolysis of
lead(II) bromide, PbBr2 molten lead(II) bromide, PbBr2

B Electrolysis of ionic compound in aqueous state

1. Prepare the apparatus set-up with an electrolytic cell half-filled with 0.1 mol dm–3
copper(II) sulphate solution, CuSO4, and two test tubes filled completely with
0.1 mol dm–3 copper(II) sulphate solution, CuSO4 (Figure 6.6).

0.1 mol dm–3 Test tube
copper(II) sulphate Carbon electrodes
solution, CuSO4

Crocodile clip

Switch +–

Light bulb

+–
Battery

Figure 6.6

2. Turn on the switch for 5 minutes. Observe and record the changes that happen to the
light bulb.

6.1.2 181

Observation: Condition of light bulb Inference
Material

Solid
lead(II) bromide, PbBr2

Molten
lead(II) bromide, PbBr2

0.1 mol dm–3
copper(II) sulphate solution, CuSO4

Conclusion:
Are the hypotheses accepted? What is the conclusion for this experiment?

Questions:
1. Why should the electrolysis of molten lead(II) bromide, PbBr2, be carried out in a

fume chamber?
2. What is the purpose of connecting a light bulb to the electrolytic cell?
3. Why does electrolysis not occur in ionic compounds that are in the solid state?

Factors Affecting the Products in Electrolysis

Three factors which affect the selection of ions to be discharged at the electrodes in the
electrolysis of aqueous solutions are:

• position of ions in the electrochemical series
• concentration of electrolyte
• types of electrode

Science

When a positive ion is discharged, the ion will receive one or more electrons, become neutral, and form
an atom or a molecule. When a negative ion is discharged, the ion will donate one or more electrons,
become neutral, and form an atom or a molecule.

182 6.1.2 6.1.3

Chapter 6 Electrochemistry

Position of Ions in the Electrochemical Series

In the electrochemical series, metals are arranged according to the tendency of their atom
to donate electron(s). The higher the position of a metal in the electrochemical series,
the easier it is for the metal to donate electron(s). Figure 6.7 shows the arrangement of
ions in the electrochemical series according to their tendency to be discharged.

Cation Ease of Anion
discharge
Potassium ion, K+ increases Fluoride ion, F –
Sodium ion, Na+ Sulphate ion, SO42–
Calcium ion, Ca2+
Magnesium ion, Mg2+ Nitrate ion, NO3–
Aluminium ion, Al3+ Chloride ion, Cl –
Zinc ion, Zn2+ Bromide ion, Br –
Iron(II) ion, Fe2+
Iodide ion, I –
Tin ion, Sn2+ Hydroxide ion, OH –
Lead(II) ion, Pb2+
Hydrogen ion, H+
Copper(II) ion, Cu2+
Silver ion, Ag+

Figure 6.7 Arrangement of ions in the electrochemical series according to their
tendency to be discharged

Ions at the bottom of the electrochemical series have higher tendencies to be discharged.

Example 1

Electrolysis of sodium sulphate solution
(a) Ions present in a sodium sulphate solution during electrolysis are sodium ions,

sulphate ions, hydrogen ions and hydroxide ions
(b) Cathode (negative electrode)

(i) Attracts positive ions, namely sodium ions and hydrogen ions
(ii) Hydrogen ions are selected to be discharged because the hydrogen ion is

less electropositive compared to the sodium ion
(iii) Hydrogen gas is produced at the cathode
(c) Anode (positive electrode)
(i) Attracts negative ions, namely sulphate ions and hydroxide ions
(ii) Hydroxide ions are selected to be discharged because the hydroxide ion is

less electronegative compared to the sulphate ion
(iii) Oxygen gas is produced at the anode

6.1.3 183

Example 2

Electrolysis of copper(II) sulphate solution
(a) Ions present in a copper(II) sulphate solution during electrolysis are copper(II)

ions, sulphate ions, hydrogen ions and hydroxide ions.
(b) Cathode (negative electrode)

(i) Attracts positive ions, namely copper(II) ions and hydrogen ions
(ii) Copper(II) ions are selected to be discharged because the copper(II) ion is

less electropositive compared to the hydrogen ion
(iii) Copper is deposited at the cathode
(c) Anode (positive electrode)
(i) Attracts negative ions, namely sulphate ions and hydroxide ions
(ii) Hydroxide ions are selected to be discharged because the hydroxide ion is

less electronegative compared to the sulphate ion
(iii) Oxygen gas is produced at the anode

Experiment 6.2

Aim: To study the effect of the position of ions in the electrochemical series
on the tendency of the ion to be discharged at the electrode

Problem statement: How does the position of ions in the electrochemical series affect the
tendency of the ion to be discharged at the electrode?

Hypothesis: The lower the position of an ion in the Cation Anion
Variables: electrochemical series, the easier it is K+ F–
for the ion to be discharged. Na+ SO42–
Materials: Ca2+ NO3–
Apparatus: (a) manipulated : Position of ion in the Cl –
electrochemical series Mg2+
Br –
(b) responding : Product at electrode Al3+
(c) constant : Concentration of I–
Zn2+
electrolyte and type OH–
of electrode Fe2+
Ease of
0.5 mol dm–3 magnesium nitrate Sn2+ discharge
solution, Mg(NO3)2, 0.5 mol dm–3 Pb2+ increases
sodium sulphate solution, Na2SO4 and H+
wooden splinter Cu2+
Ag+
Battery, carbon electrodes, connecting
wires with crocodile clips, electrolytic Figure 6.8 Arrangement of
cell, ammeter, test tubes and switch ions in the electrochemical
series according to their
tendency to be discharged

184 6.1.3

Chapter 6 Electrochemistry

Procedure: Test tube

1. Prepare the apparatus set-up with an electrolytic Carbon +– Magnesium
cell half-filled with 0.5 mol dm–3 magnesium nitrate electrodes nitrate
solution, Mg(NO3)2. +– solution,
Crocodile Battery Mg(NO3)2
2. Fill completely two test tubes with 0.5 mol dm–3 clip
magnesium nitrate solution, Mg(NO3)2, and invert Switch A Ammeter
both test tubes in the electrolytic cell (Figure 6.9).
Figure 6.9
3. Turn on the switch. Observe and record the
changes that occur at the anode and cathode.

4. Turn off the switch when the test tube is almost
full with gas released from the electrode.

5. Test the gas released using a glowing wooden
splinter and a burning wooden splinter.

6. Observe and record the results.
7. Repeat steps 1 to 6 by replacing magnesium nitrate

solution, Mg(NO3)2, with sodium sulphate solution,
Na2SO4.

Science Glowing Burning wooden splinter Burning
wooden test (test for hydrogen gas) wooden
Glowing wooden splinter splinter • Bring a burning wooden splinter
test (test for oxygen gas)
• Insert a glowing wooden splinter close to the mouth
of the test tube containing
splinter into the test tube the gas.
containing the gas. • If the gas explodes with a
• If the glowing wooden ‘pop’ sound, the gas in the
splinter ignites, the gas in test tube is hydrogen.
the test tube is oxygen.

Observation: Test for gas released at

Electrolyte anode cathode
Magnesium nitrate
solution, Mg(NO3)2 Glowing wooden splinter test: Glowing wooden splinter test:

Sodium sulphate Burning wooden splinter test: Burning wooden splinter test:
solution, Na2SO4
Glowing wooden splinter test: Glowing wooden splinter test:
Burning wooden splinter test: Burning wooden splinter test:

Conclusion: 185
Is the hypothesis accepted? What is the conclusion for this experiment?

6.1.3

Questions:

1. Name the ions in the following solutions:
(a) magnesium nitrate solution, Mg(NO3)2
(b) sodium sulphate solution, Na2SO4

2. Based on your observations in Experiment 6.2, name the gas produced at the anode and
cathode for each electrolyte in the table below.

Electrolyte Product formed at

Magnesium nitrate solution, Mg(NO3)2 anode cathode
Sodium sulphate solution, Na2SO4

3. Name the ion selected to be discharged at the anode and cathode for each electrolyte in
the table below.

Electrolyte Ion selected to be discharged at

Magnesium nitrate solution, Mg(NO3)2 anode cathode
Sodium sulphate solution, Na2SO4

Concentration of Electrolyte

The concentration of ions in an electrolyte also affects the selection of ion to be discharged.
Negative ions which are more concentrated in an electrolyte are more likely to be discharged
at the anode. However, the selection of positive ions to be discharged at the cathode is still
influenced by the position of the positive ions in the electrochemical series.

Example

Electrolysis of concentrated sodium chloride solution and dilute
sodium chloride solution
(a) Ions present in a concentrated or dilute sodium chloride solution during

electrolysis are sodium ions, chloride ions, hydrogen ions and hydroxide ions.
(b) Cathode (negative electrode)

(i) Attracts positive ions, namely sodium ions and hydrogen ions
(ii) Hydrogen ions are selected to be discharged because the hydrogen ion is

less electropositive compared to the sodium ion
(iii) Hydrogen gas is produced at the cathode
(c) Anode (positive electrode)
(i) Attracts negative ions, namely chloride ions and hydroxide ions
(ii) The negative ion discharged at the anode is influenced by the concentration

of the negative ion in the electrolyte as follows:

186
6.1.3

Chapter 6 Electrochemistry

• the concentration of chloride ion is higher than the concentration of
hydroxide ion in a concentrated sodium chloride solution such as
1.0 mol dm–3 sodium chloride solution, therefore the chloride ion will be
selected to be discharged even though the position of the chloride ion is
higher than the hydroxide ion in the electrochemical series. Chlorine gas is
produced at the anode.

• the concentration of chloride ion is lower than the concentration of
hydroxide ion in a dilute sodium chloride solution such as
0.0001 mol dm–3 sodium chloride solution, therefore the hydroxide ion will
be selected to be discharged because it is less electronegative compared to
the chloride ion. Oxygen gas is produced at the anode.

Experiment 6.3

Aim: To study the effect of concentration CAUTION!
of ions in electrolytes on the selection
of ion to be discharged at the anode Chlorine gas is poisonous.

Problem statement: How does the concentration of hydrochloric acid, HCl, influence
the selection of ion to be discharged at the anode?

Hypothesis: Ions of a higher concentration will be selected to be discharged
at the anode

Variables: (a) manipulated : Concentration of ion in electrolyte
(b) responding : Product at anode
(c) constant : Type of electrode

Materials: 1.0 mol dm–3 hydrochloric acid, HCl, 0.0001 mol dm–3 hydrochloric acid,
HCl and wooden splinter

Apparatus: Battery, carbon electrodes, connecting wires with crocodile clips,
electrolytic cell, ammeter, test tubes, litmus paper and switch

Procedure: Test tube

1. Prepare the apparatus set-up with an Carbon Hydrochloric acid,
electrolytic cell half-filled with electrodes HCl
1.0 mol dm–3 hydrochloric acid, HCl.
Crocodile clip +–
2. Fill completely two test tubes with
1.0 mol dm–3 hydrochloric acid, HCl, and Switch +–
invert both test tubes in the electrolytic Battery
cell (Figure 6.10). A Ammeter

3. Turn on the switch. Observe and record
the changes which occur at the anode.

4. Turn off the switch when the test tube
is almost filled with gas released from
the anode.

Figure 6.10

6.1.3 187

5. Test any gas released using a glowing wooden splinter, and moist blue and red litmus papers.

6. Observe and record the results of the gas tests.
7. Repeat steps 1 to 6 by replacing 1.0 mol dm–3 hydrochloric acid, HCl, with

0.0001 mol dm–3 hydrochloric acid, HCl.

Science

Moist blue litmus paper test Moist blue Moist red litmus paper test Moist red
• Place a piece of moist blue litmus paper • Place a piece of moist red litmus paper

litmus paper close to the litmus paper close to the

mouth of the test tube mouth of the test tube

containing the gas. containing the gas.

• If the moist blue litmus paper • If the moist red litmus paper

turns red, the gas in the test turns blue, the gas in the test

tube is acidic. tube is alkaline.

• If the colour of the moist blue • If the moist red litmus paper

litmus paper bleaches, the gas in does not change colour, the

the test tube is halogen gas. gas in the test tube is acidic

• If the moist blue litmus paper or neutral.

does not change colour, the gas in

the test tube is alkaline or neutral.

Observation: Test for gas produced at the anode

Electrolyte Glowing wooden splinter test:
1.0 mol dm–3 Moist blue litmus paper test:
hydrochloric acid, HCl Moist red litmus paper test:

0.0001 mol dm–3 Glowing wooden splinter test:
hydrochloric acid, HCl Moist blue litmus paper test:
Moist red litmus paper test:

Conclusion:
Is the hypothesis accepted? What is the conclusion for this experiment?

Questions:
1. What is the difference in the concentration of chloride ion, Cl–, between 1.0 mol dm–3

hydrochloric acid, HCl and 0.0001 mol dm–3 hydrochloric acid, HCl?
2. Based on your observations in Experiment 6.3, name the product formed at the anode of

each of the following electrolytes:
(a) 1.0 mol dm–3 hydrochloric acid, HCl
(b) 0.0001 mol dm–3 hydrochloric acid, HCl
3. Name the ion selected to be discharged at the anode of each of the following electrolytes:
(a) 1.0 mol dm–3 hydrochloric acid, HCl
(b) 0.0001 mol dm–3 hydrochloric acid, HCl

188 6.1.3

Chapter 6 Electrochemistry

Types of Electrode

The type of electrode used also affects the selection of ion to be discharged as follows:

(a) If the metal used as the anode is the same as the metal ion in the electrolyte, then
• at the anode, the metal atoms will ionise to form positive ions that dissolve into
the electrolyte
• at the cathode, the metal ions will discharge to form atoms of the metal which
are then deposited at the cathode
• the concentration of metal ions in the electrolyte does not change because the
rate of metal atoms ionised to form metal ions at the anode is the same as the
rate of metal ions discharged to form metal atoms which are then deposited at
the cathode

(b) If the type of substance used as the anode is not the same as the type of metal
ion in the electrolyte, then
• the atoms of the anode do not dissolve in the electrolyte. Negative ions in the
electrolyte are discharged at the anode
• at the cathode, the less electropositive ion will be selected to be discharged

Example

Electrolysis of silver nitrate solution using:

• Silver electrode
(a) Ions present in a silver nitrate solution during electrolysis are silver ions,
nitrate ions, hydrogen ions and hydroxide ions.
(b) Cathode (negative electrode)
(i) Attracts positive ions, namely silver ions and hydrogen ions
(ii) Silver ions are selected to be discharged because the silver ion is less
electropositive compared to the hydrogen ion
(iii) Silver is deposited at the cathode
(c) Anode (positive electrode)
(i) Forms silver ions when silver atoms at the anode ionise. Nitrate ions and
hydroxide ions are not discharged
(ii) The silver electrode dissolves in the electrolyte
(d) The concentration of silver ions in the electrolyte does not change because
the rate of silver atoms ionised to form silver ions at the anode is the same as
the rate of silver ions discharged to form silver atoms which are deposited at
the cathode.

• Carbon electrode
(a) Ions present in a silver nitrate solution during electrolysis are silver ions,
nitrate ions, hydrogen ions and hydroxide ions.

6.1.3 189

(b) Cathode (negative electrode)
(i) Attracts positive ions, namely silver ions and hydrogen ions
(ii) Silver ions are selected to be discharged because the silver ion is less
electropositive compared to the hydrogen ion
(iii) Silver is deposited at the cathode

(c) Anode (positive electrode)
(i) Attracts negative ions, namely nitrate ions and hydroxide ions
(ii) Hydroxide ions are selected to be discharged because the hydroxide ion is
less electronegative compared to the nitrate ion
(iii) Oxygen gas is produced at the anode

(d) The concentration of silver ions in the electrolyte decreases because the silver
ions from the electrolyte are discharged to become silver atoms and deposited
at the cathode.

Experiment 6.4

Aim: To study the effect of the type of electrode on the selection of ion to
be discharged at the electrode

Problem statement: How does the type of electrode affect the selection of ion to be
discharged at the anode?

Hypotheses: 1. If carbon electrodes are used during the electrolysis of
copper(II) sulphate solution, CuSO4, then the hydroxide ion, OH–,
is selected to be discharged at the anode.

2. If copper electrodes are used during the electrolysis of
copper(II) sulphate solution, CuSO4, then the copper(II) ion, Cu2+,
is formed at the anode.

Variables: (a) manipulated : Type of electrode (carbon or copper)
(b) responding : Product of electrolysis at the anode
(c) constant : Type and concentration of electrolyte

Materials: 0.1 mol dm–3 copper(II) sulphate Carbon
Apparatus: solution, CuSO4 and wooden splinter electrodes

Battery, carbon electrodes, copper Copper(II) sulphate
electrodes, connecting wires with solution, CuSO4
crocodile clips, electrolytic cell,
ammeter, test tubes and switch

Procedure: Ammeter –
A+
1. Prepare the apparatus set-up with an electrolytic
cell half-filled with 0.1 mol dm–3 copper(II) sulphate +–
solution, CuSO4. Switch Battery

2. Fill completely a test tube with 0.1 mol dm–3 Figure 6.11
copper(II) sulphate solution, CuSO4 and then invert
the test tube at the anode (Figure 6.11).

190 6.1.3

Chapter 6 Electrochemistry

3. Turn on the switch for 15 minutes. Observe and record the changes that occur at
the anode.

4. Test any gas released using a glowing wooden splinter.
5. Observe and record the result of the gas test.
6. Repeat steps 1 to 4 by replacing the carbon electrodes with copper electrodes.

Observation:

Type of electrode Glowing wooden splinter test at anode
Carbon electrode
Copper electrode

Conclusion:
Are the hypotheses accepted? What is the conclusion for this experiment?

Questions:
1. Name the ions present in the electrolyte during electrolysis.
2. Name the ions selected to be discharged or the ions produced at the anode for the

following types of electrodes:
(a) carbon electrode
(b) copper electrode

Application of Electrolysis in Industries

Examples of applications of electrolysis in industries include:

(a) Extraction of metals
In Form 3, you have studied the position of metals in the reactivity series of metal
and methods of metal extraction from their ores. Metals like potassium, sodium,
calcium, magnesium and aluminium are extracted from their molten ores or salts
through electrolysis.

(b) Purification of metals
In the purification of metal, the impure metal is used as the anode while the
pure metal is used as the cathode. During electrolysis, the metal at the anode will
dissolve into the electrolyte to form ions. These ions will move to the cathode to be
discharged and deposited at the cathode as pure metal.

(c) Electroplating of metals
In the process of electroplating a metal, gold, platinum and silver are electroplated
on other metals to make the metal look more attractive and to withstand corrosion.

(d) Wastewater treatment using electrocoagulation
Electrocoagulation is an innovative technique to treat wastewater (Figure 6.12).
Electrocoagulation applies two processes, namely electrolysis and coagulation.

6.1.3 6.1.4 191

• Electrolysis

➊ At the anode, a metal Floc floating in

electrode such as e– hydrogen gas bubble e– Cathode

aluminium ionises in the Floating Al3+ 4 H2 2 such as
floc H+ carbon
electrolyte to produce 1 Hydrogen
Metal anode Al3+ OH– gas bubble
positively charged such as
aluminium ions, Al3+. aluminium 3 OH– H+ Pollutant
➋ At the cathode, hydrogen sheet
ions, H+ are selected to 5
Floc
be discharged to form

hydrogen gas. Hydrogen

gas bubbles are released Wastewater

from the cathode and rise Sedimented

to the water surface. floc

• Coagulation Figure 6.12 Electrocoagulation
➌ Coagulation occurs when

aluminium ions, Al3+, hydroxide ions, OH– and pollutants in the wastewater

combine to produce coagulants known as floc.

➍ Floc, trapped in hydrogen gas bubbles released from the cathode, are brought

up to the water surface.

➎ The remaining flocs sinks and accumulates at the base.

Formative Practice 6.1

1. Draw and label the structures of an electrolytic cell.
2. Describe the movement of ions to electrodes during electrolysis.
3. Give four examples of applications of electrolysis in industries.

6.2 Chemical Cell

A simple chemical cell is made up of two Voltmeter
different metals immersed in an electrolyte V
and connected to an external circuit with
connecting wires (Figure 6.13). –+

Observe the simple chemical cell which Magnesium Copper
is made up of magnesium and copper
electrodes in Figure 6.14 and the Copper(II) sulphate
electrochemical series in Figure 6.15. solution, CuSO4

Figure 6.13 Example of a simple
chemical cell

192 6.1.4 6.2.1

Chapter 6 Electrochemistry

V ION

Voltmeter Potassium ion, K+
Sodium ion, Na+
– + Calcium ion, Ca2+ Increasing electropositivity
Copper Magnesium ion, Mg2+
Magnesium Aluminium ion, Al3+
Zinc ion, Zn2+
Copper(II) sulphate Iron(II) ion, Fe2+
solution, CuSO4
Tin ion, Sn2+
Lead(II) ion, Pb2+
Hydrogen ion, H+
Copper(II) ion, Cu2+
Silver ion, Ag+

Figure 6.14 Simple chemical cell Figure 6.15 Electrochemical series
showing arrangement of ions in
order of electropositivity

By referring to the simple chemical cell in Figure 6.14, magnesium becomes the
negative terminal and copper becomes the positive terminal. This is because magnesium
is more electropositive than copper (Figure 6.15). Magnesium is more likely to donate
electrons compared to copper.

• Magnesium which donates electrons forms • Electrons from magnesium are received by the
magnesium ions and dissolves in the copper(II) ion from the electrolyte and not by the
electrolyte (copper(II) sulphate solution). hydrogen ion because the copper(II) ion is less
electropositive than the hydrogen ion.
• Magnesium acts as the negative terminal of
the chemical cell. • Solid copper is formed and deposited on the
copper strip.
• The released electrons will flow through the
external circuit from magnesium to copper • Copper acts as the positive terminal of the
which acts as the positive terminal of the chemical cell.
chemical cell.

• The flow of electrons from Flow of V Flow of
the negative terminal to the electrons Voltmeter electrons
positive terminal through
the external circuit will Magnesium –+ Copper
produce electrical energy.
Copper(II) sulphate
• Conversion of energy which solution, CuSO4
occurs in the chemical cell
is from chemical energy to
electrical energy.

Figure 6.16 Chemical reactions in a chemical cell with different metal electrodes

6.2.1 193

Activity 6.2 21st Century Skills

To build a simple chemical cell • TPS
• Inquiry-based activity

Materials

Sandpaper, two magnesium ribbons, two copper strips and 1.0 mol dm–3 sodium chloride
solution, NaCl

Apparatus
Measuring cylinder, beaker, connecting wires with crocodile clips and voltmeter

Instructions Magnesium Voltmeter
ribbon
1. Clean two magnesium ribbons and V
two copper strips with sandpaper.
Switch
2. Measure and pour 150 cm3 of 1.0 mol dm–3 –+
sodium chloride solution, NaCl into a clean
beaker using a measuring cylinder. Copper
strip
3. Immerse a magnesium ribbon and a copper
strip into the sodium chloride solution, NaCl, Sodium chloride
in the beaker. solution, NaCl

4. Connect the magnesium ribbon, copper Figure 6.17 Simple chemical cell
strip and voltmeter with connecting
wires (Figure 6.17).

5. Turn on the switch. Observe and record the
voltmeter reading.

6. Repeat steps 1 to 5 by replacing the
magnesium ribbon and copper strip with
a pair of magnesium ribbons and a pair of
copper strips.

Result

Pair of metals Voltmeter reading (V)
Magnesium – copper
Magnesium – magnesium
Copper – copper

Application of Chemical Cell Concept in Generating Electrical
Energy from a Variety of Sources

Can fruits or other parts of a plant and seawater be used to generate electrical energy?
Let us carry out Activity 6.3 to generate ideas on how the concept of chemical cell can
be applied to generate electrical energy from a variety of sources.

194 6.2.1 6.2.2

Chapter 6 Electrochemistry

Activity 6.3

To generate electrical energy from fruits or other plant parts and seawater 21st Century Skills
Instructions
• TPS, STEM
• STEM project-

based activity

1. Carry out this activity in groups to generate ideas on how the concept of
chemical cell can be applied to generate electrical energy from a variety of sources.
Study the following statement:

The generation of electrical energy can be obtained from a variety of sources.
For example, a simple chemical cell is a device which can convert chemical energy
into electrical energy.

2. Plan and carry out a project based on the STEM approach. Build a simple chemical cell
which can convert chemical energy into electrical energy from various sources such as fruits
or other plant parts and seawater.

3. Gather and discuss information or ways to construct a simple chemical cell from fruits or
other plant parts and seawater from the following websites:

Related websites
(a) Electrical energy produced from fruits

http://buku-teks.com/sc5195a

(b) Electrical energy produced from vegetables
http://buku-teks.com/sc5195b

4. Present your simple chemical cell design to the class.

Formative Practice 6.2

1. What is a simple chemical cell?
2. Draw and label a simple chemical cell.
3. How does the position of an ion in the electrochemical series determine the

positive terminal and the negative terminal in a simple chemical cell?

6.2.2 195

196 Summary

Electrochemistry

Study in the field of chemistry on the relationship between chemical and electrical phenomena

Electrolytic cell Chemical cell

Anode, cathode, anion, cation, electrolyte and electrical source Electrolyte and two different types of metals

Electrical energy to chemical energy Chemical energy to electrical energy

Electrolysis Chemical changes that occur in cell
at
Products of electrolysis Applications in industries
Metal rod, electrolyte
affected by factors Extraction of metal, purification
of metal, electroplating of metal,
Position of ions in the treatment of wastewater through
electrochemical series, electrocoagulation
concentration of electrolyte
and types of electrode

Chapter 6 Electrochemistry

Self-Reflection

After studying this chapter, you are able to:

6.1 Electrolytic Cell 6.2 Chemical Cell
Understand electrolysis. Explain the energy change in a
Carry out experiments to study simple chemical cell.
electrolysis of ionic compounds in Generate ideas on the application
various conditions. of the chemical cell concept in
Carry out experiments to study generating electricity from a variety
the factors affecting the products of sources.
in electrolysis.
Communicate about the application
of electrolysis in industries.

Summative Practice 6 Quiz
http://buku-
Answer the following questions: teks.com/
sc5197
1. Figure 1 shows an apparatus set-up to study the electrolysis
–
of an aqueous copper(II) sulphate solution, CuSO4 using
different electrodes as shown in electrolytic cell P and

electrolytic cell Q.

+– +

Carbon Copper

Aqueous

copper(II) sulphate
solution, CuSO4

Electrolytic cell P Electrolytic cell Q

Figure 1

(a) State the meaning of electrolysis.

(b) State all the ions present in the aqueous copper(II) sulphate solution.

(c) Name the ions discharged at the anode and cathode for the following

electrolytic cells:

(i) electrolytic cell P (ii) electrolytic cell Q

at anode: at anode:

at cathode: at cathode:

(d) Name one example of the application of electrolysis in industries which applies
the electrolysis concept of electrolytic cell Q.

197

2. Figure 2 shows an apparatus set-up to study the electrolysis of aqueous
sodium nitrate solution, NaNO3, using carbon electrodes labelled P and Q.

Electrode P Aqueous sodium
nitrate solution, NaNO3

Electrode Q

+ –

Ammeter A

+–

Battery

Figure 2

(a) (i) State all the cations present in the electrolyte.
(ii) State all the anions present in the electrolyte.

(b) Which electrode acts as the anode?
(c) Name the ion chosen to be discharged at:

(i) electrode P:
(ii) electrode Q:
(d) Explain your answer in 2(c)(ii) based on the selection of ion to be
discharged.

3. Rohani found a rusted iron nail. Using your knowledge of electrolysis, describe a
simple way to prevent the rusting of the iron nail.

Enrichment Practice

4. You are given three potatoes, three iron nails, three copper rods, light bulb and
connecting wires with crocodile clips. Using these materials, design a simple
chemical cell with the following features:

(a) simple chemical cell that can light up a light bulb with maximum brightness.
(b) simple chemical cell that can last the longest when lighting up a light bulb.

198

3HEME The Swedish 1-m Solar
Telescope in La Palma, Spain
Energy and has a convex lens as the
Sustainability objective lens with a diameter of
of Life approximately 1.10 m. Why do
astronomers need to observe
outer space through the
telescope all the time, that is,
24 hours a day?

The drone is a scientific
invention that is becoming
increasingly popular.
Name one physics
principle applied in the
flight of a drone.

Click@Web

Biggest telescope in
the world
http://buku-teks.com/sc5199a

Look through a
‘live’ telescope
http://buku-teks.com/sc5199b

199

7CHAPTER LIGHT AND
OPTICS

Name the types of lenses used
to correct long-sightedness
and short-sightedness.

State one advantage of liquid
lens compared to glass lens.

Besides thickness, name
one factor which affects
the focal length of lens.

Let’s study

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t 0QUJDBM JOTUSVNFOUT

200

Science Bulletin

Nowadays, the use of lenses in optical instruments is
expanding. For example, the telephone which was originally an
audio communication device has been developed into a
smartphone which can function as an audio-visual
communication device using a camera to take photographs
and videos.

Handphone without Smartphone with
camera five cameras

Camera quality is normally related to the type or
quality of lens attached to the camera. This is because
the image in the camera is formed by the lens. Besides
transparent glass and plastic, any transparent material
including water can be used to make lenses. The concept
of liquid lens is shown in the photograph below.

Concept of liquid lens

Keywords r 3BZ EJBHSBN r .BHOJGZJOH QPXFS
r 1SJODJQBM BYJT r 5FMFTDPQF
r $POWFY MFOT r 0QUJDBM DFOUSF r /PSNBM BEKVTUNFOU
r $POWFSHJOH MFOT r 0CKFDU EJTUBODF r CCTV
r $PODBWF MFOT r *NBHF EJTUBODF r -FOTFT JO PQUJDBM
r %JWFSHJOH MFOT r .JDSPTDPQF
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201

7.1 Formation of Images by Lenses

Convex Lens and Concave Lens

A lens is a transparent medium such as glass which has one or two curved surfaces.
Lenses are divided into two types, convex lens and concave lens as shown in
Figure 7.1.

Biconvex Planoconvex Convex meniscus

Convex lens

Biconcave Planoconcave Concave meniscus
Concave lens

Figure 7.1 Convex lens and concave lens

Figure 7.2 shows the path of light rays before and after passing through a
convex lens and a concave lens. What happens to the light rays after passing through
these lenses?

Figure 7.2 Refraction of light rays after passing through a convex lens and a concave lens

Based on Figure 7.2, light rays converge after passing through a convex lens while
light rays diverge after passing through a concave lens. Therefore, a convex lens is known
as a converging lens while a concave lens is known as a diverging lens.

202 7.1.1

Chapter 7 Light and Optics

For convex lenses, the focal point, F is a point where light rays parallel to the
principal axis converge after passing through the convex lens (Figure 7.3(a)).

Convex lens Concave lens

Principal axis Focal point, Focal point Principal axis
F F

Focal length, f Focal length, f

(a) Convex lens (b) Concave lens

Figure 7.3 Focal point and focal length for convex lens and concave lens

When light rays which diverge after passing through a concave lens are extrapolated
backwards, the light rays will intersect at a point. This point is the focal point, F for
the concave lens (Figure 7.3(b)).

Let us carry out Activity 7.1 to study some properties of convex lenses and concave
lenses using an Optical Ray Kit.

Activity 7.1 21st Century Skills

Use the Optical Ray Kit to: • TPS
(a) show the convex lens as a converging lens and the concave lens as a • Inquiry-based activity

diverging lens
(b) determine the focal points of convex lenses and concave lenses

Materials
White paper (sized 86 cm × 86 cm)

Apparatus

Optical Ray Kit containing ray box, cylindrical biconvex lens, cylindrical biconcave lens,
triple slit plate, ruler and pencil

Note: This activity is best suited to be carried out in the dark.

7.1.1 203

Instructions

Ray box Triple slit Cylindrical
plate biconvex lens

Path of parallel rays

White paper

Figure 7.4

1. Prepare the apparatus set-up shown in Figure 7.4. Video
2. Trace the shape of the convex lens onto a piece of white

paper using a pencil. Mark the centre point of the convex Eduweb TV:
lens, that is the optical centre, O on the tracing of the Physics – lenses
convex lens. http://buku-teks.
3. Direct three parallel light rays from the ray box in the com/sc5204

direction of the convex lens. Observe the path of light (Medium: bahasa

rays before and after passing through the convex lens. Melayu)

4. Make two marks, one near to the lens and another far

from the lens, on each path of the light rays before and

after passing through the convex lens. Remove the convex lens from the white paper.

5. Draw a straight line using a pencil and ruler to connect the two marks on each path of the

light rays before and after passing through the convex lens (Figure 7.3(a)).

6. Mark the point of intersection of the three light rays as the focal point, F for the

convex lens.

7. Repeat steps 1 to 5 by replacing the convex lens with a concave lens.

8. Extrapolate the light rays which diverge after passing through the concave lens backwards

until a point of intersection (Figure 7.3(b)).

9. Mark the point of intersection of the three light rays as the focal point, F for the

concave lens.

Questions

1. Why is it more suitable for this activity to be carried out in the dark?
2. What happens to light rays after passing through the following lenses?

(a) Convex lens
(b) Concave lens
3. Describe the observations made in this activity that show the following properties of lenses:
(a) convex lens as a converging lens
(b) concave lens as a diverging lens

204 7.1.1

Chapter 7 Light and Optics

Determining the Focal Length of a Convex Lens

Before carrying out Activity 7.2, let us understand optical terms (Table 7.1).

Axis of lens

Object

Principal axis O F 2F
2F F Image

ff

uv

(a) Convex lens
Axis of lens

Object

Principal axis Image O
F
2F F 2F
v

ff
u
(b) Concave lens

Figure 7.5 Convex lens and concave lens

Table 7.1 Optical terms and their explanations

Optical term Explanation
Optical centre, O
Point at the centre of the lens. Light rays which pass through the
Principal axis optical centre do not refract.

Axis of lens A straight line which passes through the optical centre of a lens and the
focal point, F.
Focal point, F
(refer to Straight line which passes through the optical centre and is perpendicular
Figure 7.3) to the principal axis.

Focal length, ƒ • For convex lens, the focal point, F is a point on the principal axis,
Object distance, u where light rays parallel to the principal axis converge after passing
Image distance, ν through the lens.

• For concave lens, the focal point, F is a point on the principal axis,
where light rays parallel to the principal axis appear to diverge from it
after passing through the lens.

The distance between the focal point, F and the optical centre.

The distance between the object and the optical centre.

The distance between the image and the optical centre.

7.1.2 205

Let us carry out Activity 7.2 to determine the Parallel oF
focal length of a convex lens using a distant light rays O
object by applying the concept that light rays from a
from a distant object are parallel (Figure 7.6). distant f
object

Activity 7.2 Figure 7.6

To determine the focal length of a convex lens using a distant object 21st Century Skills
Materials
• TPS
Convex lens, lens holder, white screen and metre rule • Inquiry-based activity

Instructions

1. Prepare the apparatus set-up as shown Laboratory window

in Figure 7.7.

2. Position the convex lens towards a Convex lens White screen

distant object seen through an open

window. Lens holder
3. Adjust the position of the white screen

until a sharp image of the distant

object is formed on the screen. Figure 7.7
4. Measure and record the distance

between the centre of the convex lens and the screen, that is the focal length, f of the

convex lens using a metre rule.

Questions

1. Why are laboratory objects not used to determine the focal length of a convex lens in
this activity?

2. State the characteristics of the image formed on the white screen.
3. If the convex lens in this activity is replaced with a concave lens, can the focal length of the

concave lens be estimated? Explain your answer.

Ray Diagrams to Determine the Characteristics of Images
Formed by Convex Lenses and Concave Lenses

Besides carrying out activities using appropriate apparatus Video
such as in Activity 7.2, the position and characteristics of
images formed by convex lenses and concave lenses can be Steps to draw
determined using ray diagrams. ray diagrams
http://buku-teks.
Study and understand Table 7.2 which explains the com/sc5206
method of drawing ray diagrams by drawing two principal (Medium: bahasa
light rays to determine the characteristics of the images Melayu)
formed by convex lenses and concave lenses.

206 7.1.2 7.1.3

Chapter 7 Light and Optics
Table 7.2 Method for drawing ray diagrams

Convex lens
1 A light ray parallel to the principal axis refracts and passes through the focal point, F.

Object 1 1
F F

2 A light ray heading towards the optical centre continues in a straight line through the
optical centre without refracting.

Object 1
2
1 Real image
F F

2

Concave lens

1 A light ray parallel to the principal axis refracts and appears to come from the
focal point, F.

1

Object 1

FF

2 A light ray heading towards the optical centre continues in a straight line through the
optical centre without refracting.

Object 1 1
F
2
2
F Virtual
image

7.1.3 207

Tables 7.3 and 7.4 show the positions of object, ray diagrams, positions of image and
characteristics of images for convex lens and concave lens, respectively.

Table 7.3 Ray diagrams to determine the characteristics of images formed by a convex lens

Position of Ray diagram Position of Characteristics
object
image of image

Object is Object F 2F Image is • Real
further than 2F Image between F • Inverted
2F and 2F • Diminished

F

Object is Image is at • Real
at 2F 2F • Inverted
• Same size as
Object F F 2F
2F Image object

Object is Object F 2F Image is • Real
between F 2F further • Inverted
and 2F than 2F • Magnified

F

Image

Object is Image is at • Virtual
at F infinity • Upright
• Magnified
Object F 2F
2F F

Object is Image Image • Virtual
between F distance • Upright
and optical is further • Magnified
centre than F

(Used as a Object F
magnifying F
glass)
7.1.3
208

Chapter 7 Light and Optics

Table 7.4 Ray diagrams to determine the characteristics of images formed by a concave lens

Position of Ray diagram Position of Characteristics
object
image of image

Object is Between • Virtual
further
than 2F optical • Upright

Object centre and • Diminished

F Image focal point

2F F 2F

Object is Between • Virtual
between F
and optical optical • Upright
centre
Object centre and • Diminished
2F F Image
focal point

F 2F

Note: The characteristics of images formed by concave lenses for any object distance are:

• virtual BRAIN
• upright TEASER
• diminished

• positioned between the object and the concave lens Reinforcement practice

http://buku-teks.com/sc5207

Formative Practice 7.1

1. Name the type of lens found in the human eye.
2. Figure 1 shows two types of lenses.

Lens X Lens Y

Figure 1

(a) Name the following types of lenses:

(i) Lens X (ii) Lens Y

(b) (i) Which lens functions as a diverging lens?

(ii) Which lens functions as a converging lens?

(c) Mark the focal point of lenses X and Y with the letter F.

3. How is the convex lens used as a magnifying glass?

7.1.3 209

7.2 Optical Instruments

The function of optical instruments is normally related to the type of image, whether
real or virtual, and the size of image formed by the lens. The ray diagrams in Tables 7.3
and 7.4 show that the image size
formed by a lens depends
on the position of the object
from the centre of the lens.

Magnifying glass Microscope Astronomical telescope

Photograph 7.1 Optical instruments

Photograph 7.1 shows three optical instruments. Describe the characteristics of the final
image formed by these three optical instruments.

Formation of the Final Image by a Microscope Scan
Page

Study the two ray diagrams in Figure 7.8.

(a) Object is between F and 2F (b) Object is between F and the optical centre, O
Objective lens Eyepiece

Object F 2F F O F
2F F
O Object
Image Image

Image position: Image is further than 2F Image position: Image is further than F
Image characteristics: • Real Image characteristics: • Virtual

• Inverted • Upright
• Magnified • Magnified

Figure 7.8 Ray diagrams for the images formed by the objective lens and eyepiece of a microscope

210 7.2.1

Chapter 7 Light and Optics

Based on your understanding of the two ray diagrams in Figure 7.8, the formation of
the final image by a microscope is shown in Figure 7.9.

Objective lens Eyepiece

Object First Construction lines
Fe
2Fo image,
Fo Fe Io
Virtual
final Fo
image,
I

Figure 7.9 Ray diagram showing the formation of the final image in a microscope

Determining the Magnifying Power of a Microscope

Magnifying power of microscope
= Magnifying power of objective lens × Magnifying power of eyepiece

Example Science

Photograph 7.2 shows a microscope containing an Identify the
eyepiece with a magnifying power of 4 times and an objective lens
objective lens with a and eyepiece of
magnifying power a microscope
of 40 times. http://buku-teks.
com/sc5211

Photograph 7.2 211

Calculate the magnifying power of the microscope.

Solution
Magnifying power of microscope
= Magnifying power of objective lens × Magnifying power of eyepiece
= 40 × 4
= 160 times

7.2.1

Formation of the Final Image by a Telescope

Study the two ray diagrams in Figure 7.10.

(a) Object at infinity (b) Object at F
Objective lens
Eyepiece

FF 2F F F 2F
Image Object

Image position: Image at F Image position: Image at infinity
Image characteristics: • Real Image characteristics: • Virtual

• Inverted • Upright
• Diminished • Magnified

Figure 7.10 Ray diagrams for the images formed by the objective lens and eyepiece of
a telescope

Based on your understanding of the two ray diagrams in Figure 7.10, the formation of
the final image by a telescope is shown in Figure 7.11.

Parallel incident fo fe Fe
rays from a
distant object Fo
Fe
Fo First image, Io

Objective lens Virtual final image Eyepiece
at infinity, I

Figure 7.11 Ray diagram showing the formation of the final image in a telescope

In normal adjustment, the distance between the objective lens and eyepiece = ƒo + ƒe
where ƒo = focal length of objective lens,

ƒe = focal length of eyepiece
so that the image can be viewed more comfortably.

212 7.2.1