SUCCESS CHEMISTRY

H H H H H H H H H H H H H H H
| | | | | | | | | | | | | | |

H–C–C–C–C–C–C–C–H H–C–C–C–C–C–C–C–C–H
| | | | | | | | | | | | | | |
H H H H H H H H H H H H H H H

heptane (C7H16) octane (C8H18)

H H H H H H H H H H H H H H H H H H H
| | | | | | | | | | | | | | | | | | |

H–C–C–C–C–C–C–C–C–C–H H–C–C–C–C–C–C–C–C–C–C–H
| | | | | | | | | | | | | | | | | | |
H H H H H H H H H H H H H H H H H H H

nonane (C9H20) decane (C10H22)

Physical Properties of Alkanes

1 On going down the alkane series, the physical properties change gradually as shown in Table 2.3.

Table 2.3 Physical properties of alkanes

Name of Molecular Relative molecular Melting point Boiling point Physical Density
alkane formula state (g cm–3)
2 Methane mass (°C) (°C) Gas
Ethane CH4 Gas —
Propane C2H6 16 –182 –162 Gas —
Butane C3H8 Gas —
Pentane C4H10 30 –183 –89 Liquid —
Hexane C5H12 Liquid 0.626
Heptane C6H14 44 –188 –42 Liquid 0.659
Octane C7H16 Liquid 0.684
Nonane C8H18 58 –138 –0.5 Liquid 0.703
Decane C9H20 Liquid 0.718
C10H22 72 –130 36 0.730

86 –95 69

100 –90 98

114 –57 126

128 –54 151

142 –30 174

2 Melting and boiling points of alkanes Figure 2.2 The boiling points of alkanes increase
(a) Alkanes exist as simple covalent molecules. with relative molecular mass
Alkanes have low melting and boiling
points because of the weak van der Waals
forces between molecules. Little energy is
required to overcome the weak forces of
attraction.
(b) When the number of carbon atoms per
molecule of alkane increases, the relative
molecular mass increases and the melting
point and boiling point increase. This
is because the larger the molecular size,
the stronger the van der Waals forces of
attraction between the molecules.

3 The physical states of alkanes
The first four members are gases as
their boiling points are below room
temperature (25 °C). The alkanes from C5

Carbon Compounds 344

to C18 are liquids with the rest of the alkanes SPM CH4 + Cl2 → CH3Cl + HCl
being solids.
4 Densitites of alkanes ’05/P1 chloromethane
Alkanes are less dense than water. The density
of alkanes increases gradually down the series CH3Cl + Cl2 → CH2Cl2 + HCl
as the molecular mass increases.
5 Solubility of alkanes dichloromethane
(a) All alkanes are insoluble in water. When
CH2Cl2 + Cl2 → CHCl3 + HCl
liquid alkane is shaken with water, two
separate layers of liquids are formed. trichloromethane
(b) Alkanes are soluble in organic solvents
such as propanone. CHCl3 + Cl2 → CCl4 + HCl
6 Electrical conductivity of alkanes
All alkanes do not conduct electricity because tetrachloromethane
they are covalent compounds, consisting of
molecules. In the substitution reaction obfoCnHds4, weiitthheCr lb2,otnhdeecdartbooHn
atom still has four covalent

atom or Cl atom.

Chemical Properties of Alkanes H Cl Cl

1 Reactivity of alkanes | Cl2 | Cl2 |
H — C — H ⎯→ H — C — H ⎯→ H — C — Cl
Alkanes are saturated hydrocarbons and are less 2

reactive compared to unsaturated hydrocarbons. | | |
H H H
2 Combustion of alkanes
CH3Cl CH2Cl2
(a) Alkanes undergo complete combustion
1 H substituted 2 H substituted
in the presence of excess air or oxygen to

produce carbon dioxide and water. Cl Cl

SPM For example Cl2 | Cl2 |
’05/P1,
’11/P2 CH4 + 2O2 → CO2 + 2H2O ⎯→ H — C — Cl ⎯→ Cl — C — Cl

methane | |

2C2H6 + 7O2 → 4CO2 + 6H2O Cl Cl

ethane CHCl3 CCl4
3 H substituted 4 H substituted
(b) The combustion of alkanes is highly
exothermic, that is, produces a lot of heat The Effects of Methane on Everyday Life
energy. Hence alkanes are used as fuels.
1 Methane, commonly known as natural gas, is
(c) Incomplete combustion of alkanes will used as a fuel.
produce carbon (black smoke), carbon
monoxide and water. 2 It is produced by the anaerobic decay of
plants and organic matter by bacteria.
(d) The larger the molecular size of the alkane Hence methane is found in landfills and peat
swamps.
molecule,
(i) the smokier or sootier the flame, 3 Methane is a greenhouse gas. It can trap
(ii) the more heat produced on complete radiation energy from the sun and also
contribute to global warming.
combustion.
3 Substitution reactions Methane is also known as marsh gas because it is
found in marshes and stagnant ponds. It can cause
SPM (a) When a mixture of alkane and chlorine fires in garbage landfills and peat swamps.
’10/P1 is exposed to sunlight or ultraviolet light,

substitution reaction occurs slowly and
a mixture of organic compounds and
hydrogen chloride is produced.
(b) In a substitution reaction, the hydrogen
atoms in an alkane are replaced gradually

by chlorine atoms.

For example The reaction between methane

and chlorine

345 Carbon Compounds

2.2 9 The names and molecular formulae of the first
nine members of the alkene series are shown
1 Name and give the molecular formula of an alkane in Table 2.4.
with
(a) three carbon atoms Table 2.4 The names and molecular formulae of the
(b) five carbon atoms first nine members of the alkene series
(c) six carbon atoms
Number of Prefix Name of Molecular
2 Petrol used in cars consists mainly of octane. carbon atoms alkene formula
(a) Give the molecular formula of octane. per molecule
(b) Write an equation for the complete combustion
of octane. 2 Eth Ethene C2H4

3 Ethane reacts with chlorine under certain conditions 3 Prop Propene C3H6
to form chloroethane.
(a) State the condition for reaction to take place. 4 But Butene C4H8
(b) Name the reaction that takes place.
(c) Write an equation for the reaction that occurs. 5 Pent Pentene C5H10

4 A saturated hydrocarbon X has a relative molecular 6 Hex Hexene C6H12
mass of 58. Identify X. [Relative atomic mass:
H, 1; C, 12] 7 Hept Heptene C7H14

2 2.3 Alkenes 8 Oct Octene C8H16

1 Alkenes are hydrocarbons with the general 9 Non Nonene C9H18
formula CnH2n, where n = 2, 3, 4….
10 Dec Decene C10H20
2 Alkenes are unsaturated hydrocarbons and
contain at least one double bond between 10 The structural formulae of the first nine
carbon atoms. straight chain alkenes with one terminal
double bond (double bonds at the end of a
3 The functional group in alkenes is the carbon- chain) are shown as follows:
carbon double bond (C=C).
H H
4 The molecular formula of an alkene can be | |
obtained by substituting n in the general
formula CnH2n with the number of carbon H–C=C–H
atoms. ethene

5 In the naming of alkenes according to the H H H
IUPAC system, all members of the alkene | | |
series have their names ending with -ene.
H–C–C=C–H
6 The first part (prefix) of the name of an alkene |
depends on the number of carbon atoms in H
the molecule.
propene
7 The first member of the alkene series is ethene,
C2H4 because there must be a minimum of two H H H H
carbon atoms to form a carbon-carbon double | | | |
bond (C=C). Hence methene does not exist.
H–C–C–C=C–H
8 Note that when writing the structural formula | |
of alkenes, H H
(a) there is a carbon-carbon double bond
(C=C) in the chain. butene
(b) each carbon atom forms four bonds (four
single bonds or one double bond + two H H H H H
single bonds). | | | | |
(c) each hydrogen atom should have one
single covalent bond. H–C–C–C–C=C–H
| | |
H H H

pentene

Carbon Compounds 346

H H H H H H 2 Similarly, the carbon chain of an alkane drawn as a
| | | | | | straight chain is the same as that drawn in a bent
chain.
H–C–C–C–C–C=C–H
| | | | H H H H
H H H H | | | |
H — C — C — C — C — H is the same as
hexene | | | |
H H H H
H H H H H H H H
| | | | | | | |
H—C—H
H–C–C–C–C–C–C=C–H H H
| | | | | | |
H H H H H
H—C—C—C—H
heptene | | |
H H H
H H H H H H H H
| | | | | | | | Physical Properties of Alkenes

H–C– C–C–C–C–C–C=C–H 1 The physical properties of alkenes are the 2
| | | | | | same as that of alkanes.
H H H H H H
Low melting and Insoluble in water
octene boiling points due to but soluble in
weak van der Waals organic solvents
H H H H H H H H H forces between molecules such as propanone
| | | | | | | | |
Physical properties
H–C–C–C–C–C–C–C–C=C–H of alkenes
| | | | | | |
H H H H H H H

nonene

H H H H H H H H H H Do not conduct Less dense than
| | | | | | | | | | electricity because water hence will float
they consist of on the surface of
H–C–C–C–C–C–C–C–C–C=C–H covalent molecules water
| | | | | | | |
H H H H H H H H

decene

1 In the drawing of the structural formula of an alkene, 2 The physical properties change gradually on
the hydrogen atom bonded to the carbon atom can going down the alkene series as shown in
be written as (a) bonded to the side or (b) to the top
or (c) bottom of the carbon atom. This is because Table 2.5.
the single covalent bond can be rotated freely. 3 Similar to that of alkanes, the melting points

H H H H and boiling points of alkenes increase down
| | | | the homologous series. When the number
H — C = C — H or C = C or H — C = C — H
| | | | of carbon atoms per molecule increases, the

H H H H molecular size increases. Thus the van der

Waals forces of attraction between molecules
increases, increasing the amount of heat
needed to overcome the forces of attraction
during melting or boiling.
4 Similar to that of alkanes, the density of
alkenes increases gradually down the series as
the molecular mass increases.

347 Carbon Compounds

Table 2.5 Physical properties of alkanes

Name of Molecular Relative Melting point Boiling point Physical state at Density
alkene formula room temperature (g cm–3)
Ethene molecular mass (°C) (°C)
Propene C2H4 Gas –
Butene C3H6 28 –169 –104 Gas –
Pentene C4H8 Gas –
Hexene C5H10 42 –185 –48 Liquid 0.64
Heptene C6H12 Liquid 0.67
Octene C7H14 56 –130 –6 Liquid 0.70
Nonene C8H16 Liquid 0.72
Decene C9H18 70 –138 30 Liquid 0.73
C10H20 Liquid 0.74
84 –140 64

98 –119 93

112 –104 122

126 –94 146

140 –66 171

2 Chemical Properties of Alkenes (c) Alkenes undergo addition reactions. During

1 Combustion of alkenes addition reactions, the carbon-carbon
SPM (a) Alkenes burns in excess air or oxygen to double bond breaks open to form two
’07/P1 form carbon dioxide and water. Heat energy new single bonds. In this process, the
unsaturated hydrocarbon is converted to
is released during combustion.
a saturated compound.
C2H4 + 3O2 → 2CO2 + 2H2O
2C3H6 + 9O2 → 6CO2 + 6H2O | | | |

(b) The combustion of an alkene is more —C=C—+X—Y→—C—C—
luminous and smokier than an alkane with
the same number of carbon atoms. This is alkene | |
because the percentage by mass of carbon in (unsaturated) X Y
an alkene is higher than that of an alkane.
Example (saturated)
Percentage by mass of carbon in hexene
(Mr of C6H12 = 84) one double bond two new single bonds
= —6—3—8—4—1—2 3 100 = 85.7%
Percentage by mass of carbon in hexane 3 The following are examples of addition
(Mr of C6H14 = 86) reactions between alkenes and other elements/
= —6—3—8—6—1—2 3 100 = 83.7% compounds:
(a) Hydrogen (hydrogenation)
(c) Incomplete combustion of alkenes (b) Halogens (halogenation)
produces carbon (black smoke) and carbon (c) Water (hydration)
monoxide. (d) Acidified potassium manganate(VII) solution
(e) Hydrogen halides
2 Addition reactions of alkenes
(a) Addition reactions are reactions in 4 Hydrogenation
which an unsaturated organic compound (a) Hydrogenation is the addition of a hydrogen
combines with another compound to molecule across a carbon-carbon double
form a single new saturated compound. bond in the presence of nickel or platinum
(b) Alkenes contain a double bond between as a catalyst. An alkene is converted to an
carbon atoms (C = C bond) which is very alkane.
reactive. Hence alkenes are more reactive
than alkanes. For example

SPM C3H6 + H2 ⎯N⎯i o⎯r Pt→ C3H8

’07/P1

propene propane

(b) Hydrogenation is used to make margarine
(in solid form) from vegetable oils (in liquid
form).

Carbon Compounds 348

5 Halogenation | |
—C ⎯ C—
SPM (a) The addition reactions between alkenes
’10/P1, | |
’11/P2 and halogens (chlorine and bromine) are OH OH

called halogenation.

(b) Bromination is used as a chemical test to (c) In the formation of a diol, two hydroxyl
(–OH) groups are added across the double
distinguish alkanes from alkenes. Alkenes bond in the alkene molecule.
For example:
decolourise the brown colour of liquid

bromine whereas alkanes do not decolourise

the brown colour of liquid bromine. C2H4 + H2O + [O] → C2H4(OH)2

For example: When ethene is passed into ethene ethane-1, 2-diol

liquid bromine, the brown colour of (d) Like liquid bromine, acidified potassium

bromine is decolourised immediately and manganate(VII) solution is used to

a colourless organic liquid is formed. distinguish between alkane and alkene

⎯tem⎯rpo⎯eorma⎯tur→e 1,2-diCbr2oHm4oBerth2ane

C2H4 + Br2 compounds. An alkene decolourises the
bromine
ethene purple colour of acidified potassium

(saturated) manganate(VII) solution whereas an alkane

6 Hydration does not.

(a) Hydration occurs when a water molecule is 8 Polymerisation

added across the double bond between the Alkenes undergo polymerisation to form

atoms in the presence of phosphoric(V) polymers. Activity 2.2 2

acid with H3PO4 as a catalyst at 300 °C. SPM (a) Ethene undergoes additional polymerisation
SPM (b) An alkene is converted to an alcohol in ’07/P1,
’07/P2 hydration. For example ’06/P1 to form polyethene.

H H H H
| | polymerisation |
eCth2eHne4 + H2O ⎯300⎯°H⎯C3P, ⎯O604⎯atm→ C2H5OH C C ⎯⎯⎯⎯⎯→ C |
nH — = — H — — C —
ethanol ethene | |

7 Reaction with acidified potassium H H n
manganate(VII) solution
(a) When an alkene reacts with acidified polyethene

potassium manganate(VII) solution, the (b) Propene undergoes polymerisation to
purple colour of potassium manganate(VII) form polypropene.
is decolourised immediately and an
organic compound called diol is formed. H H H H CH3
(b) A diol is a saturated alcohol with two | | | polymerisation | |
C C—C ⎯⎯⎯⎯→
hydroxyl (–OH) groups on adjacent carbon nH — = — H C—C
| | |
atoms.
H H H n

propene polypropene

To compare the chemical properties of alkanes and alkenes
having the same number of carbon atoms SPM

’11/P2

Apparatus Procedure
A Combustion of alkanes and alkenes in air
Porcelain dish, wooden splint, dropper and Bunsen
burner. EXUQLQJ VSOLQW ILOWHU SDSHU
SRUFHODLQ
Materials GLVK
Hexane, hexene, liquid bromine and acidified
potassium manganate(VII) solution.

KH[DQH KH[DQH
RU KH[HQH RU KH[HQH

Figure 2.3 Combustion of alkane and alkene

7&

349 Carbon Compounds

1 About 1 cm3 of hexane and hexene are placed 3 The mixture is shaken gently.
separately into two separate porcelain dishes. 4 The colour change that takes place in the test

2 The organic liquids are ignited with a burning tube is recorded.
splint. 5 Steps 1 to 4 are repeated using hexene.

3 A piece of filter paper is held above the C Reactions with acidified potassium
flames in each of the dishes to detect the manganate(VII) solution
amount of soot formed. 1 A few drops of potassium manganate(VII)
solution are placed in a test tube, followed
4 The sootiness of the flame and the amount by about 1 cm3 of dilute sulphuric acid.
of soot collected on the two pieces of filter 2 About 2 cm3 of hexane is then added to the
papers are recorded. acidified potassium manganate(VII) solution.
3 The mixture is shaken gently.
B Reactions with bromine 4 The colour change that occurs in the test tube
1 About 1 cm3 of liquid bromine is placed in a is recorded.
test tube. 5 Steps 1 to 4 are repeated using hexene.
2 About 2 cm3 of hexane is then added to the
liquid bromine.

Results

Test Observations
Combustion
2 Hexane Hexene
Reaction with liquid bromine
Burns in air with a sooty flame Burns in air with a more sooty
Reaction with acidified potassium yellow flame
manganate(VII) solution
The brown colour of liquid The brown colour of liquid
bromine remains unchanged bromine is decolourised

The purple colour of potassium The purple colour of potassium
manganate(VII) solution remains manganate(VII) solution is
unchanged decolourised

Conclusion

The chemical properties of hexene are different from those of hexane:
(a) Both hexane and hexene undergo combustion but the flame of hexene is sootier than that of hexane.
(b) Hexene decolourises the brown colour of liquid bromine whereas hexane does not.
(c) Hexene decolourises the purple colour of acidified potassium manganate(VII) solution whereas hexane does

not.

Discussion

1 The combustion of hexene produces more soot than the combustion of hexane. This is because the percentage
by mass of carbon in hexene is higher than that of hexane.

2 Hexene undergoes addition reaction with bromine:

C6H12 + Br2 → C6H12Br2

(brown) 1, 2-dibromohexane

(colourless)

3 Hexene undergoes addition reaction with acidified potassium manganate(VII)

C6H12 + H2O + [O] → C6H12(OH)2

from KMnO4 hexane-1,2-diol
(purple) (colourless)

Carbon Compounds 350

In the addition reaction of an alkene for example with Br H Br
chlorine, the product formed has the two Cl atoms | | |
bonded to the two C atoms adjacent to each other. C H — C — C — C — H
Products with two Cl atoms bonded to the same C | | |
atom or across another C atom are not formed. H H H
Example: Addition of chlorine to propene cannot form H H H
| | |
the following products: D H — C — C — C — Br
| | |
H H Cl H H H H H H

| | | | | | Solution
Propene undergoes addition reaction with Br2 at the
H — C — C — C — H and H — C — C — C — H carbon-carbon double bond, hence the product formed
has two Br atoms attached to two adjacent C atoms.
| | | | | |
Answer: B
H H Cl Cl H Cl

1 ’05 Homologous Series 2

The following is the equation that represents the 1 A homologous series is a family of organic
reaction between propene and bromine. compounds with the same functional group
and with similar chemical properties.
Propene + Br2 → P
2 A functional group is an atom or a group of
Which of the following is the structural formula of atoms that determines the chemical properties
P? of an organic compound.
Br H H
| | | 3 All members in the same homologous series
A H — C — C — C — H have the same functional group and the same
| | | chemical properties.
Br H H
4 All members in the same homologous series
H H Br (a) have the same general formula
| | | (b) can be prepared using similar methods
B H — C — C — C — H (c) show a gradual change in their physical
| | | properties
H Br H (d) have similar chemical properties
(e) differ from each other by a –CH2 group

5 General formulae of some homologous series
are shown in Table 2.6.

SPM

Table 2.6 General formulae of some homologous series ’07/P2

Homologous series General formula Functional group

Alkanes CnH2n+2 –
Alkenes CnH2n
Alcohols CnH2n+1OH – C = C – (double bond)
Carboxylic acids CnH2n+1COOH
– O – H (hydroxyl group)

O
i

– C – O – H (carboxyl group)

Esters CnH2n+1COOCmH2m+1 O
i

– C – O – (carboxylate group)

351 Carbon Compounds

CnH2n+2
alkane

– (CnH2n)n – Hydrogenation CnH2nX2
polymer H2/Ni, 180 °C

CnH2n+1OH Addition CnH2n Addition of halogen, X2
alcohol polymerisation alkene
Addition of hydrogen
Addition of water, halide, HX
H603PaOtm4, 180 °C,
Addition of CnH2n+1X
acidified KMnO4

CnH2n(OH)2
diol

2

2.3 4 Isomers have different physical properties
because they have different structural
1 (a) What is the general formula of alkene? formulae.
(b) Give the molecular formula of an alkene with
5 For methane, ethane and propane, there is
(i) three carbon atoms only one structure. Therefore methane, ethane
(ii) five carbon atoms and propane do not have isomers. All the
(iii) seven carbon atoms other alkanes, have isomers.

2 Propane and propene are both hydrocarbons. 6 There are two different ways of arranging the
(a) State two common physical properties between four carbon atoms and ten hydrogen atoms for
propane and propene. butane, C4H10. Thus butane has two isomers
(b) State one common chemical property between as follows:
propane and propene.
(a) Straight chain
3 Write chemical equations for the reactions between (all 4 C atoms form a straight chain)
propene with
(a) chlorine H H H H
(b) water | | | |
(c) hydrogen
(d) excess oxygen H—C—C—C—C—H
(e) acidified potassium manganate(VII) | | | |
H H H H
2.4 Isomerism SPM
(b) Branched chain
’10/P1, (3 C atoms form a straight chain with
’10/P2, 1 C atom forming a branch)
’11/P2
H
1 Isomers are compounds which have the |
same molecular formula but with different H—C—H
structural formulae. H H
| |
2 Isomerism is the existence of two or more
H—C—C—C—H
compounds that have the same molecular | | |
H H H
formula but with different structural formulae.
3 Isomers will have the same chemical properties

when they have the same functional group.

Carbon Compounds 352

7 There are three different ways of arranging the five carbon atoms and twelve hydrogen atoms in
pentane, C5H12. Thus C5H12 has three isomers.

(a) Straight chain (b) One branched chain (c) Two branched chains
(5 C atoms form a straight (4 C atoms form a straight (3 C atoms form a straight
chain) chain with 1 C atom chain with 2 C atoms
forming a branch) forming two branches)
H H H H H
| | | | | H H
H—C—C—C—C—C—H | |
| | | | | H—C—H
H H H H H H H H H—C—H
| | |
H—C—C—C—C—H H H
| | | | | |
H H H H
H—C—C—C—H
| |

H H

H—C—H
|

H

8 All the alkenes above propene have isomers. Butene, C4H8 has three isomers as follows: 2

(a) Straight chain with a (b) Straight chain with a double (c) Branched chain
double bond at the end of bond in the middle of the (3 C atoms form a straight
the chain chain chain with a double bond and
(4 C atoms form a straight (4 C atoms form a straight 1 C atom forming a branch)
chain with a double bond chain with a double bond H
at the first C atom) at the second C atom) |

H H H H H H H H H—C—H
| | | | | | | | H H
H—C=C—C—C—H | |
| | H—C—C=C—C—H
H H | | H—C=C—C—H
|
H H H

9 Naming of branched isomers of alkanes according to the IUPAC system

Step 1 For example:

Find the longest continuous chain of carbon H
atoms in the molecule and name the longest |
chain as the parent chain. H—C—H
H H H
| | |

H—C—C—C—C—H
| | | |
H H H H

The longest chain has four carbon atoms. The
name of the parent chain is butane.

353 Carbon Compounds

Step 2 Formula and name of alkyl groups
1 Name the branched chain attached to the
Number of carbon atoms Formula Name
parent chain as alkyl group. 1 Methyl
2 The alkyl groups are named according to the 2 –CH3 Ethyl
3 –C2H5 Propyl
number of carbon atoms present. –C3H7
The alkyl group has the general formula CnH2n+1
where n = 1, 2, 3… H –CH3 (methyl group)
| is attached to the
Step 3 H—C—H parent chain of four
Identify the position of the alkyl group that is
attached to the parent chain by number. H H H carbon atoms
(a) This is done by numbering the carbon atom in | | |
H—C—C—C—C—H
the parent chain using the lowest number.
(b) Use hyphens to separate words from numbers | | | |

in the name, for example: 2 – methyl. H H H H

2 Step 4
1 If there are more than one similar branch, use
For example:
the following prefixes
(a) di for two similar branched chains H
(b) tri for three similar branched chains |
(c) tetra for four similar branched chains
2 Name the positions of carbon atoms in the H—C—H –CH3 (methyl group)
parent chain containing the branches. For is attached to carbon
example, the positions of two branches may H H H number 2
be 2, 2 or 2, 3. | | |

H — C1 — C2 — C3 — C4 — H
| | | |

H H H H

The name of the alkane is 2-methyl butane

carbon side chain is parent chain has
no. 2 –CH3 four carbon atoms

For example: H
|

H—C—H

H H H
| | |

H—C—C—C—C—H
| | |

H H H
H—C—H
|

H

2,2–dimethyl butane

both –CH3 branches two –CH3 parent chain has
attached to carbon no. 2 branches four carbon atoms

Carbon Compounds 354

Step 5 For example:

If there are more than one alkyl group, list the H H C2H5 CH3 H H
names of the alkyl groups in alphabetical order. | | | | | |

H—C—C—C—C—C—C—H
| | | | | |
H H H H H H

3-ethyl,4-methylhexane

10 Naming of alkenes according to the IUPAC system SPM

’11/P1

Step 1 For example
H
1 Select the longest carbon chain with the |
double bond (C=C) as the parent alkene.
H—C—H
2 Name the parent alkene according to the
number of carbon atoms. H H
| |
2
H—C=C—C—H

|
lhoansgefosut rcchaaribnownitahtoCm=sC H

Step 2 H H H H double bond
| | | | present
1 Select the position of the double bond by
choosing the smallest number for the carbon H — C1 — C2 == C3 — C4 — H
atom with the C=C bond. | |
H H
2 Name the position of the double bond with a
number followed by a hyphen, for example: Correct name but-2-ene
2-ene.
parents chain has 4 double bond at
carbon atoms carbon no. 2

Wrong name but-3-ene

3, the larger number is not used

Step 3 Example methyl group at carbon
H no. 2
Identify the alkyl group and its position in the |
parent chain as fixed in Step 2.
H—C—H

H H H

| | |

H—C—C=C—C—H

| |

H H

2-methylbut-2-ene

–CH3 group at carbon no. 2 C=C at carbon no. 2

355 Carbon Compounds

1 To choose the longest carbon chain as the parent chain, count the number of carbon atoms which could be in a

straight chain or a bent chain.

For example: –C– This is the longest
| chain with 6 C atoms

–C–
|
–C–C=C–C–C–

2 The alkyl group bonded by a single covalent bond to a carbon atom can rotate in a molecule. It may be drawn as
up or down or at the side in a 2-D structural formula.
For example: These two structures below are not isomers, they are the same compound.

H
|
H—C—H

H H H H H H
| | | | | |
H — C — C = C — C — H H—C—C=C—C—H
| |
| |
H H H H

H—C—H
|
2 H

3 The following alkene does not exist because the central carbon atom has five covalent bonds.

C
|

C=C—C
|
C

4 The following alkene structures are the same, they are not isomers.

(a) C = C — C — C — C is the same as C — C — C — C = C

(b) C = C — C — C; C — C — C = C; C — C — C — C are the same isomer.
| | i
C C C

2.4

1 Give the IUPAC name of the following compounds: (c) H H H H

(a) H | | | | ⎯H
H ⎯C ⎯C ⎯C = C ⎯C
| | | | |
H—C—H
H H — C — H H — C — H H
H H H
|
| | | |
H—C—C=C—C—H H H

| | 2 Draw and name all the isomers for C5H10.
H H
3 Ethane reacts with chlorine in the presence of sunlight
(b) H
to form a substituted product with the molecular
|
formula of Cth2iHs 4pCrlo2.dDucrat.wWahnicdh name all the possible
H H — C — H H H H isomers of of the isomer is also

| | | | | formed when ethene reacts with chlorine in the
H⎯C⎯ C ⎯ C⎯ C=C⎯H
| | addition reaction?
|
H H H — C — H

|

H

Carbon Compounds 356

2.5 Alcohols 7 All alcohols above ethanol have isomers. The
position of the hydroxyl (–OH) group and
1 Alcohols have the general formula CnH2n+1OH the alkyl group are shown by numbering the
where n = 1, 2, 3… The CnH2n+1– group carbon atoms from the end of the carbon
represents the alkyl group. chain which gives the smallest number to the
–OH group.
2 The functional group of alcohol is the
hydroxyl (–OH) group. The hydroxyl (–OH) 8 Propanol, C3H7OH has two isomers:
group is joined to the carbon atom in the
alcohol molecule by a single covalent bond. Structural formula IUPAC name

3 The molecular formula of an alcohol can (a) H H H parent chain has three
be obtained by substituting n in the general | | | carbon atoms
formula CnH2n+1OH with the number of
carbon atoms. H–C–C–C–H Correct name propan-1-ol
| | |
4 Based on the IUPAC system of naming O H H position of the –OH group
straight chain alcohols, the letter e at the end | is at the first carbon atom
name of alkane is replaced by the suffix ol. For H
example Wrong name propan-3-ol
CH4 (methane) → CH3OH (methanol) The –OH group is at
C2H6 (ethane) → C2H5OH (ethanol) the first carbon atom 3, the bigger number
is not used
2

Alkane Alkane Alcohol Alcohol formula (b) H H H The parent chain has
Methane formula Methanol | | | three carbon atoms
(CnH2n+2) CH3OH
C2H5OH H–C–C–C–H propan-2-ol
CH4 C3H7OH | | |
C4H9OH H O H position of the –OH group
Ethane C2H6 Ethanol | is at the second carbon atom
H
Propane C3H8 Propanol
The –OH group is at the
Butane C4H10 Butanol second carbon atom

5 Note that when writing the structural formula 9 Butanol, C4H9OH has four isomers as
of alcohols, follows:
(a) each carbon atom should have four single
covalent bonds. Structural formula IUPAC name
(b) each hydrogen atom should have one
single covalent bond. (a) parent group has
(c) each oxygen atom has two single covalent H H H H four carbon atoms
bonds. | | | |
(d) the carbon atoms are connected by single H–C–C–C–C—H butan-1-ol
bonds. | | | |
O H H H position of the –OH group
6 Methanol and ethanol has one structural | is at the first carbon atom
formula each. Hence they have no isomers. H
parent group has
H H H (b) four carbon atoms
⎮ ⎮ ⎮ H H H H
H — C — H H—C—C—H ⎮ ⎮ ⎮ ⎮ butan-2-ol
⎮ ⎮ ⎮ H–C–C–C–C—H
O O H ⎮ ⎮ ⎮ ⎮ position of the –OH group
⎮ H O H H is at the second carbon
H ⎮ ⎮ atom
H H
methanol
ethanol

357 Carbon Compounds

Structural formula IUPAC name Example H H H

(c) methyl group | | |

H at second methyl group at H—C—C—C—H
| carbon atom second carbon atom
| | |
H—C—H 2-methylpropan-1-ol
O O O
H H
| | | | |
H–C–C–C–H parent group position of the
has three –OH group H H H
carbon atoms is at the first
carbon atom three-OH groups

propan-1,2,3-triol

| | | parent group has three-OH groups
three carbon atoms at 1st, 2nd and 3rd
O H H carbon atoms
|

H

Industrial Production of Alcohols

(d) methyl group at 1 Ethanol (C2H5OH) can be produced industrially
second carbon atom by two processes:
H
| 2-methylpropan-2-ol (a) The hydration of ethene
H — C — H
H H (b) The fermentation of sugar or starch
| |
Activity 2.3 2 parent group position of the 2 Hydration of ethene
H–C–C–C–H has three –OH group
| | | carbon atoms at second When a mixture of ethene and steam is passed
H O H carbon atom
| over the catalyst, phosphoric(V) acid (H3PO4)
H at 300 °C and high pressure (65 atm), ethanol

is produced.

3 Fermentation

When yeast is added to sugar or starch, ethanol

and carbon dioxide are produced. The enzyme

10 In the naming of an alcohol with more than one called zymase, breaks down the glucose
–OH group:
(a) di is used for two –OH groups molecules to form ethanol and carbon dioxide.
(b) tri is used for three –OH groups
SPM C6gHluc1o2Ose 6 ⎯ye⎯ast→ 2Ce2tHha5nOolH + c2aCrbOon2

’06/P1

dioxide

To prepare ethanol in the laboratory by fermentation and
distillation

Apparatus 3 The yeast paste is added to the glucose solution
and the mixture is stirred well.
Conical flask, boiling tube, thermometer, fractionating
column, wire gauze, retort stand, distillation flask, 4 The conical flask is closed with a rubber stopper
rubber stopper, delivery tube, tripod stand and fitted with a delivery tube. The other end of the
Bunsen burner. delivery tube is dipped in limewater.

Materials 5 The apparatus is left in a warm place (about 25
– 35 °C) for about one week. The changes that
Glucose, yeast, distilled water and limewater. occur in the conical flask and the test tube are
recorded from time to time.
Procedure
1 About 20 g of glucose is dissolved in 200 cm3 of 6 After about one week, the products in the
conical flask are filtered. The filtrate obtained is
distilled water in a conical flask. transferred into a distillation flask.
2 A little warm water (35 °C) is added to about 5 g
7 The filtrate is distilled in a flask fitted with a
of yeast in a small beaker. The mixture is stirred fractionating column and Liebig condenser.
well to form a paste.

Carbon Compounds 358

Figure 2.4 Fermentation process Figure 2.5 Fractional distillation

Result

1 During fermentation, ethanol and carbon dioxide are produced.
2 The carbon dioxide produced causes limewater to turn cloudy.
3 The concentration of ethanol produced in fermentation can be increased by fractional distillation.

Conclusion Activity 2.4 2
Ethanol can be prepared in the laboratory by the fermentation of glucose or any other carbohydrates.

Yeast is a living organism. Ethanol is actually a by-product 2 Ethanol is a volatile liquid because it has a
formed from the living process of yeast. The highest low boiling point at 78 °C.
concentration of ethanol prepared by fermentation is only
14%. This is because yeast is killed when the ethanol 3 Ethanol is very soluble in water because of the
formed exceeds 14%. Hence higher concentration of presence of the hydroxyl group.
ethanol has to be obtained from fractional distillation. (a) The hydrocarbon part of alcohol is insoluble
in water.
Physical Properties of Ethanol and Other (b) Hence alcohol with a large hydrocarbon
Alcohols chain is insoluble in water.
(c) The solubility of alcohols in water decreases
1 Ethanol is a colourless liquid and has a as the molecular size increases.
characteristic odour.
4 Alcohols are neutral and have a pH of 7.
5 Alcohols are covalent compounds. They do not

conduct electricity.

To investigate the chemical properties of ethanol

Apparatus

Evaporating dish, wooden splint, test tube, boiling tube, delivery tube with stopper, glass wool, porcelain chips,
beaker, retort stand with clamp and test tube holder.

Materials

Ethanol, concentrated sulphuric acid, potassium dichromate(VI), blue litmus paper and liquid bromine.

(A) Combustion of ethanol in air
Procedure
1 About 2 cm3 of ethanol is poured into an evaporating dish.
2 The ethanol is ignited using a lighted wooden splint.
3 The flammability of ethanol and the sootiness of the flame are recorded.

359 Carbon Compounds

Result 3 Acidified potassium dichromate(VI) solution is
an oxidising agent.
Nature of combustion Observation
(C) Dehydration of ethanol
Flammability Easily burned
Procedure
Colour of flame Blue
1 Some glass wool is placed in a boiling tube.
Sootiness of flame Non-sooty 2 About 2 cm3 of ethanol is poured into the boiling

2 Conclusion tube to soak the glass wool.
3 Some porcelain chips are placed in the mid-
Ethanol burns readily in air. The combustion of ethanol
produces a non-sooty, pale blue flame. The products section of the boiling tube.
of combustion are carbon dioxide and water. 4 The boiling tube is closed with a rubber stopper

(B) Oxidisation of ethanol fitted with a delivery tube. The other end of the
delivery tube is placed under an inverted test
Procedure tube filled with water in a beaker.
5 The porcelain chips are heated strongly until red
1 About 1 cm3 of concentrated sulphuric acid and hot. The Bunsen burner flame is then shifted to the
5 cm3 of potassium dichromate(VI) solution are glass wool to vaporise the ethanol absorbed in it.
poured into a boiling tube. 6 The gas is collected in two test tubes. The gas
produced is collected by displacement of water
2 About 5 cm3 of ethanol is added to the acidified and tested with
potassium dichromate(VI) solution. (a) a few drops of bromine water and shaken
(b) a few drops of acidified potassium
3 A rubber stopper fitted with a delivery tube is
inserted into the boiling tube. The delivery tube manganate(VII) solution and shaken
is inserted into a test tube placed in a beaker
half-filled with ice-cold water. SPM

4 The mixture of ethanol and acidified potassium ’05/P1
dichromate(VI) is heated gently. Any colour
change in the mixture is noted.

5 The distillate is collected in the test tube and is
tested with litmus paper.

Figure 2.7 Dehydration of ethanol

Figure 2.6 Oxidation of ethanol Result

Result Test on gas collected Observation

Compound Observation With bromine water Brown colour of
Reactant bromine is decolourised
mixture The acidified potassium
dichromate(VI) solution changes With acidified potassium Purple colour of
Distillate from orange to green manganate(VII) solution potassium manganate(VII)

A colourless liquid (a vinegary is decolourised
smell) which changes blue litmus
paper to red Conclusion

Conclusion 1 When ethanol vapour is passed over heated
porcelain chips (aluminium oxide), dehydration
1 When ethanol is boiled with acidified potassium occurs and ethene is produced.
dichromate(VI) solution, it is oxidised to ethanoic
acid. 2 Ethene is confirmed to be present by the
decolourisation of the brown colour of bromine
2 Ethanoic acid is a colourless liquid with a vinegary water and the purple colour of acidified
smell and turns blue litmus paper red. potassium manganate(VII) solution.

Carbon Compounds 360

Chemical Properties of Ethanol and (b) Dehydration is carried out by
Other Alcohols (i) passing alcohol vapour over heated

1 (a) Alcohol undergoes complete combustion porcelain chips or
SPM when it burns in excess air to produce carbon (ii) refluxing alcohol with concentrated
’08/P2 dioxide and water.
sulphuric acid (acts as a dehydrating
For example agent).
C2H5OH + 3O2 → 2CO2 + 3H2O (c) Methanol does not undergo dehydration
since there is no alkene with one carbon
ethanol atom.

C3H7OH + —92 O2 → 3CO2 + 4H2O The alcometer (breath tester) used for testing the
propanol breath of suspected drink-driver contains potassium
dichromate(VI). The chemical will oxidise any ethanol
(b) Combustion of alcohol such as ethanol present in the breath and produces an electric current. 2
gives out a lot of heat energy. Hence
ethanol is a good fuel. Uses of Alcohol in Everyday Life

(c) If the supply of oxygen is insufficient, 1 Alcohols as fuels
incomplete combustion of ethanol occurs. When alcohol is burn in air, carbon dioxide
Carbon monoxide gas, carbon (black soot) and water are produced, and a large quantity
and water are produced. of heat energy is released. Ethanol is a clean
fuel because it does not release toxic gases in
2 (a) Oxidation of alcohols produces the combustion.
corresponding carboxylic acids.
2 Alcohols as solvents
For example Alcohols are good solvents for organic
compounds such as shellac, varnishes, paints,
CH3CH2OH + 2[O] ⎯K2C⎯r2⎯O7/⎯H2⎯SO→4 perfumes and dyes.
ethanol
3 Uses of alcohols in medicines
from K2Cr2O7 CH3COOH + H2O (a) Ethanol is used as a mild antiseptic for
skin infection and disinfection.
ethanoic acid (b) Propan-2-ol is used as rubbing alcohol to
reduce fever.
CH3CH2CH2OH + 2[O] ⎯→
propanol 4 Uses of alcohols in cosmetics
(a) Ethanol is used to make aftershave lotion
CH3CH2COOH + H2O and nail polish.
propanoic acid (b) Propan-1,2,3-triol (common name is
glycerol) is used in moisturiser.
(b) Oxidation is carried out by heating the (c) Alcohols are used as solvents for perfumes.

alcohols with oxidising agents such as 5 Alcohols as a source of chemicals
(a) Ethanol is oxidised to make vinegar.
acidified potassium manganate(VII) (b) Methanol is used to make formalin and
polymers.
solution or acidified potassium
6 The misuse and abuse of alcohols
dichromate(VI) solution. (a) Ethanol is a component of alcoholic
drink. Excess drinking of alcohol increases
(c) When oxidation reaction occurs: the risk of heart disease, kidney disease
and liver disease.
(i) The colour of potassium dichromate(VI) (b) Alcoholism is an addiction caused by
excessive drinking of alcohol for a prolonged
changes from orange to green. period of time.

(ii) The colour of potassium manganate(VII)

changes from purple to colourless

(decolourisation).

3 (a) Dehydration of alcohols (except methanol)

produces the corresponding alkenes.

For example

SPM C2H5OH ⎯→ C2H4 + H2O
ethanol
’07/P2, ethene
’06/P1

C3H7OH ⎯→ C3H6 + H2O

propanol propene

361 Carbon Compounds

(c) Driving after drinking too much alcohol Number Alkane Carboxylic acid
can cause road accidents. of carbon
Methane Methanoic acid
2.5 atoms Ethane Ethanoic acid
Propane Propanoic acid
1 Compound X has a molecular formula of C4H8O. 1
When compound X is refluxed with acidified
potassium dichromate(VI), the mixture changes 2
colour from orange to green.
(a) Name the funtional group of compound X. 3
(b) What is the general formula of the homologous
series in which compound X is a member. 4 The name of the carboxylic acid will depend on
(c) Draw and name all the isomers of compound the number of carbon atoms in its molecule.
X.
(d) Write the chemical equation for the reaction The carbon atom of the functional group is
between compound X and acidified potassium
dichromate(VI). counted as part of the carbon chain.
5 The molecular formula of a carboxylic acid can
2 Identify the compounds P, Q, R, S and T from the
reaction scheme given below: be obtained by substituting n in the general

2 yeast KMnO4/ formula CnH2n+1COOH with the number of
Glucose Compound H2SO4 Compound carbon atoms.
6 In the writing of the structural formula of a
PQ carboxylic acid,

oxygen, heat porcelain chips, heat (a) the –COOH group is always at the terminal

carbon atom (at the end of the chain).
(b) the carboxyl group consists of a carbon

atom which forms a double bond with
oxygen atom and a single covalent bond
with the hydroxyl (–OH) group.

Compound R Compound O double bond
+ T i

compound S –C–O–H

3 State the type of reactions that occur and give the single bond
molecular formulae of compounds W, X, Y and Z
in the following equations. 7 The molecular and structural formulae of the
first four members of carboxylic acids are shown
(a) W ⎯co⎯nc⎯en⎯tra⎯ted⎯H⎯2S⎯O4→ C3H6 + H2O in Table 2.7.

( b) X + H2O phosphoric acid C3H7OH Table 2.7 The names and formulae of the first four
⎯⎯⎯⎯⎯⎯→ members of carboxylic acids

( c) C 4H9OH + 2[O] ⎯K2C⎯r2O⎯7/⎯H2⎯SO→4 Y + H2O Name Molecular Structural formula
formula

(d) Z + 6O2 ⎯→ 4CO2 + 5H2O Methanoic HCOOH O
acid i
H — C — OH

2.6 Carboxylic Acids Ethanoic CH3COOH O
acid i
1 Carboxylic acids are organic acids that have
the general formula CnH2n+1COOH, where n is CH3 — C — OH
0, 1, 2, 3 ….
Propanoic C2H5COOH O
2 The functional group of carboxylic acids is the acid i
carboxyl group, –COOH.
CH3 — CH2 — C — OH
3 Based on the IUPAC system of naming, a
carboxylic acid is named by replacing the Butanoic C3H7COOH O
final letter e in the name of the corresponding acid i
alkane with oic acid.
CH3 — CH2 — CH2 — C — OH

Carbon Compounds 362

Preparation of Carboxylic Acid 2 Ethanoic acid has a vinegary smell.
3 Ethanoic acid is soluble in water.
1 Carboxylic acid is prepared in the laboratory by 4 On going down the homologous series of the
the oxidation of the corresponding alcohol.
Example carboxylic acids,
Ethanol ⎯oxi⎯dat⎯ion→ ethanoic acid
Propanol ⎯oxi⎯da⎯tio→n propanoic acid (a) the solubility in water decreases,
Butanol ⎯oxi⎯dat⎯ion→ butanoic acid
(b) the boiling point increases.
2 In the laboratory, ethanoic acid is prepared by
the oxidation of ethanol using an oxidising Chemical Properties of Ethanoic Acid
agent such as
(a) acidified potassium dichromate(VI) or 1 Ethanoic acid is a weak acid because it
(b) acidified potassium manganate(VII) undergoes partial ionisation in water. Only a
small percentage of the ethanoic acid molecules
3 The method of heating a mixture of ethanol ionise to form hydrogen ions, H+. Most of the
and the oxidising agent in a flask fitted with ethanoic acid remains as molecules.
an upright Liebig condenser is known as
reflux. CH3COOH CH3COO– + H+

4 Heating under reflux is used 2 Aqueous ethanoic acid turns blue litmus paper
(a) to prevent volatile substances (ethanol
and ethanoic acid) from escaping into the red and is an electrolyte. 2
atmosphere, 3 Ethanoic acid reacts with bases to form salts
(b) to ensure that the reactants go to complete
reaction. and water in neutralisation. The salts produced
in the reaction are known as ethanoate. For
5 In the oxidation of ethanol by acidified potassium
dichromate(VI), example
(a) the colour of potassium dichromate(VI)
solution changes from orange to green. CH3COOH + NaOH → CH3COONa + H2O
(b) the ethanoic acid produced has a vinegary ethanoic acid sodium
smell.
CH3CH2OH + 2[O] ⎯K⎯2Cr⎯2O⎯7/H⎯2SO⎯4 → ethanoate
CH3COOH + H2O
2CH3COOH + CuO → (CH3COO)2Cu + H2O
Figure 2.8 Preparation of ethanoic acid by reflux ethanoic copper copper(II)

Physical Properties of Ethanoic Acid and acid oxide ethanoate
Other Carboxylic Acids
(black) (blue)
1 Ethanoic acid is a colourless liquid at room
temperature. Pure ethanoic acid is known as 4 Ethanoic acid reacts with metal carbonates
glacial ethanoic acid because it freezes to SPM to form salts, carbon dioxide and water. For
form colourless crystals which look like ice. ’05/P1 example

2CH3COOH + Na2CO3 ⎯→
2CH3COONa + CO2 + H2O

sodium ethanoate

2CH3COOH + CaCO3 ⎯→
(CH3COO)2Ca + CO2 + H2O

calcium ethanoate

5 Ethanoic acid reacts with reactive metals such
as magnesium and zinc to form salts and
hydrogen gas.
For example
2CH3COOH + Mg ⎯→ (CH3COO)2Mg + H2
magnesium ethanoate

2CH3COOH + Zn ⎯→ (CH3COO)2Zn + H2
zinc ethanoate
6 Ethanoic acid reacts with an alcohol to form
ester and water.
For example
Ethanoic acid + ethanol → ethyl ethanoate + water

(ester)

363 Carbon Compounds

To study the chemical properties of ethanoic acid

Apparatus Results Observation
Test tubes, beakers, evaporating dish, delivery tube
and wooden splints. Test Effervescence occurs
(a) Ethanoic acid + and sodium carbonate
Materials dissolves
Ethanoic acid, sodium hydroxide solution, sodium sodium carbonate
carbonate, limewater, magnesium ribbon, glacial Gas produced turns
ethanoic acid and concentrated sulphuric acid. (b) Gas released + limewater cloudy
limewater
(A) Reaction of ethanoic acid with a base
Conclusion
Procedure
1 About 3 cm3 of dilute ethanoic acid is placed in a Ethanoic acid reacts with sodium carbonate, a metal
carbonate to form a salt, carbon dioxide and water.
test tube.
2 About 3 cm3 of sodium hydroxide is added to the (C) Reaction between ethanoic acid and a metal

ethanoic acid and the mixture is shaken. Procedure SPM
3 The reaction mixture is poured into an evaporating
’11/P2
dish and is heated until it becomes dry.
Activity 2.5 2 4 The residue left in the evaporating dish is 1 About 5 cm3 of ethanoic acid is placed in a test tube.

observed. 2 A piece of magnesium ribbon is added to the

Observation ethanoic acid.
A white powder was left in the evaporating dish.
3 A lighted splint is placed near the mouth of the
Conclusion
Ethanoic acid reacts with a base, sodium hydroxide test tube to test the gas liberated.
to produce a salt and water.
Results
(B) Reactions between ethanoic acid and a metal
carbonate Test Observation
(a) Ethanoic acid +
Procedure Effervescence occurs and
1 About 5 cm3 of ethanoic acid is placed in a test magnesium the magnesium ribbon
dissolves
tube. (b) Gas released +
2 A spatula of sodium carbonate is added to the lighted splint Gas burns with a ‘pop’
sound when the lighted
ethanoic acid. splint is placed at the
3 The gas released is passed into limewater. mouth of the test tube

Figure 2.9 Reaction with ethanoic acid and a Conclusion
metal carbonate
Ethanoic acid reacts with magnesium, a metal to
form a salt and hydrogen gas.

(D) Reactions between ethanoic acid and alcohol

Procedure

1 2 cm3 of glacial ethanoic acid is placed into a test
tube.

2 4 cm3 of pure ethanol is added to the ethanoic acid.
3 About 1 cm3 of concentrated sulphuric acid is

added slowly and carefully to the mixture using
a dropper.
4 The reaction mixture is shaken and heated slowly
for about 3 minutes.
5 The content of the test tube is then poured into a
beaker half-filled with water.

Carbon Compounds 364

Figure 2.10 Reaction of ethanoic acid and ethanol

Observation 2 An ester is an organic compound formed when a 2
carboxylic acid reacts with an alcohol.
1 An oily product forms a layer on top of the
water’s surface. 3 Esterification is the reaction between a carboxylic
acid and an alcohol to produce ester and water.
2 The product is colourless and has a sweet fruity
smell. 4 Concentrated sulphuric acid acts as a catalyst
to speed up esterification.
Conclusion
5 When ethanoic acid is warmed with ethanol
1 Ethanoic acid reacts with ethanol, an alcohol to in the presence of a few drops of concentrated
form an ester and water. sulphuric acid, esterification occurs. The ester
known as ethyl ethanoate and water are produced.
2 Ester has a sweet fruity smell and is insoluble in
water. C H3COOH + C2H5OH ⎯co⎯nc.⎯H2⎯SO→4
CH3COOC2H5 + H2O
Discussion
ethyl ethanoate
1 The sweet smelling oily product is an ester.

Chemical properties of other carboxylic acids General
2RCOOH + CaCO3 →
1 All members of the carboxylic acids have
similar chemical properties because they have (RCOO)2Ca + H2O + CO2
the same functional group, –COOH. Example
2HCOOH + CaCO3 →
2 The general formula of a carboxylic acid can
also be written as RCOOH where R is H or an (HCOO)2Ca + H2O + CO2
alkyl group. 2C2H5COOH + CaCO3 →

3 All members of this carboxylic group will (C2H5COO)2Ca + H2O + CO2
(a) react with alkalis to form salts and water (d) react with alcohols to form esters and water.
General SPM General
RCOOH + NaOH → RCOONa + H2O ’06/P1 RCOOH + R′OH → RCOOR′ + H2O
Example
HCOOH + NaOH → HCOONa + H2O Example
C2H5COOH + NaOH → HCOOH + C2H5OH →
C2H5COONa + H2O
(b) react with active metals to form salts and HCOOC2H5 + H2O
hydrogen gas C2H5COOH + C2H5OH →
General
2RCOOH + Mg → (RCOO)2Mg + H2 C2H5COOC2H5 + H2O
Example
2HCOOH + Mg → (HCOO)2Mg + H2 Uses of Carboxylic Acids in Daily Life
2C2H5COOH + Mg →
(C2H5COO)2Mg + H2 Carboxylic acid Use
(c) react with metallic carbonates to form salts, Methanoic acid To coagulate latex
carbon dioxide and water Ethanoic acid To make vinegar
Benzoic acid Used as a food preservative

365 Carbon Compounds

Alkane cracking Alkene hydration Alcohol oxidation Carboxylic Acid
CnH2n+2 hydrogenation CnH2n dehydration CnH2n+2OH CnH2n+1COOH

combustion combustion esterification
combustion
Ester
Carbon dioxide and water RCOOR′

2.6 SPM 3 The functional group of esters is the carboxylate
’11/P1 group, –COO–.
1 Compound X with an empirical formula of CH2O
has a relative molecular mass of 60. 4 The name of an ester is derived from the alcohol
(a) Calculate the molecular formula of X and draw
its structural formula. and the carboxylic acid used to prepare it.
(b) Identify the functional group of X and give its (a) The first part of the name of the ester is
general formula.
(c) Write a balanced equation between X and taken from the alkyl group of the alcohol.
calcium carbonate. Predict the observation that
will take place. Example
[Relative atomic mass: of H,1; C,12; O,16]
2

2 (a) Give the name and molecular formula for a Alcohol Alkyl group
carboxylic acid that has five carbon atoms. Methanol Methyl
Ethanol Ethyl
(b) Give the molecular formula of the organic Propanol Propyl
compound formed when the carboxylic acid Butanol Butyl
named in (a) reacts with
(b) The second part of the name comes from
(i) sodium hydroxide the carboxylic acid. The ending –oic of
(ii) magnesium metal carboxylic acid is replaced by –oate.
Example
3 Compound P, with a molecular formula of C3H8O
is converted to compounds Q and R in the
following reaction scheme.

P Step I: K2Cr2O7/H2SO4 Q Carboxylic acid Carboxylate group
Methanoic acid Methanoate
Step II Ethanoic acid Ethanoate
Propanoic acid Propanoate
R
(c) In general, the names of esters are of
(a) Identify compound Q and compound R. the form ‘alkyl carboxylate’ where alkyl
(b) State the condition of reaction in Step II. comes from the alcohol used to prepare
(c) Name the types of reactions that have occurred the ester.
Example
in Steps I and II.

2.7 Esters Alcohol Carboxylic acid Names of ester
Methanol Methanoic acid Methyl methanoate
1 The general formula for an ester is Methanol Ethanoic acid Methyl ethanoate
aCnnHd 2mn+1=CO1,O2C, m3H, 42m…+1,. where n = 0, 1, 2, 3, 4… Ethanol Ethanoic acid Ethyl ethanoate
Ethanol Propanoic acid Ethyl propanoate
2 The general formula for an ester can also be
written as R–COO–R′ where R and R′ are alkyl
groups.

Carbon Compounds 366

5 In the writing of the structural formula of an Hence, the name of the ester is ethyl

ester using the general formula R–COO–R′, propanoate.
the part R– CO comes from the carboxylic acid
7 The reaction between an alcohol and a carboxylic

and the part of O– R′ comes from the alcohol. acid to produce an ester and water is known

6 Generally, O as esterification.
i
General Alcohol + carboxylic acid →
R – C – OR′ ester + water

from carboxylic acid from alcohol Example C2H5OH + CH3CH2COOH →
ethanol propanoic acid
Example O
i
O
CH3CH2C O – CH2CH3 i
CH3CH2C O–CH2CH3 + H2O
from propanoic acid from ethanol ethyl propanoate

Steps in naming an ester SPM

’07/P1,
’06/P1

Step 1 Example: the alcohol part (bonded

Identify the alcohol part of the ester. O to –O) is –CH3, hence the 2
The alcohol part is the alkyl part bonded to i prefix is methyl
oxygen atom by single bond.
CH3 — CH2 — C — O — CH3

Step 2 O
i
Identify the carboxylic acid part of the ester.
The acid part is the alkyl part bonded to the CH3 — CH2 — C — O — CH3
carbon atom with a double bond with oxygen.
the carboxylic part (with – C=O) has altogether
3 C atoms, hence it is from propanoic acid

Step 3 Name of ester is methyl propanoate

Combine the two parts to name the ester.
The alcohol part is named first.

2 ’07

The molecular formula below represents an organic Solution this is the acid part as
compound.
it is bonded to C=O this is the alcohol
O
i part as it is bonded

CH3 — C — O — CH2 — CH2 — CH3 O to O atom
i
What is the name of the compound?
CH3 — C— O — CH2 — CH2 — CH3


from ethanoic acid from propanol
(ester is ethanoate) (prefix is propyl)

The name of the compound is propyl ethanoate.

367 Carbon Compounds

Writing the structural formula of an ester SPM
’07/P1

To predict the formula of an ester prepared from Example
a named alcohol and a named carboxylic acid. Write the structural formula of the ester produced
from butanol and propanoic acid.
Step 1 General formula is

Write the general formula of ester in the form O
R – COO – R′ i

R – C – O – R′

Step 2 Alcohol is butanol, with four C atoms.
Hence R′ is –CH2CH2CH2CH3.
Write down the structural formula of the alcohol
part to replace –R′(R bonded to O by single O
bond) i

R – C – O – CH2CH2CH2CH3

2

Step 3 Carboxylic acid is propanoic acid, with three C
atoms. Hence RCO– is CH3CH2CO–.
Write down the structural formula of the acid
part to replace R– (R bonded to C=O) O
i

CH3CH2C–

Step 4 Structural formula of ester is:

Replace –OR′ with the alcohol part and the O
R–CO– with the carboxylic part in R – COO – R′ i
for the full structure of the ester. CH3 — CH2 — C — O — CH2 — CH2 — CH2 — CH3

3 ’07 Preparation of Ethyl Ethanoate

Write the chemical equation for the reaction between 1 Small quantities of ethyl ethanoate can be
methanol and ethanoic acid. prepared by heating a mixture of glacial
ethanoic acid with pure ethanol in the
Solution presence of a small quantity of concentrated
Methanol, an alcohol reacts with ethanoic acid, a sulphuric acid in a boiling tube.
carboxylic acid to produce an ester and water. The
ester will be methyl ethanoate. 2 To prepare large quantity of esters, the alcohol
and carboxylic acid need to be heated under
CH3OH + CH3COOH → CH3COOCH3 + H2O reflux.

3 Heating under reflux is necessary as ethanol,
C2H5OH is very volatile. If the mixture is not
heated under reflux, the ethanol C2H5OH will
vaporise and escape into the atmosphere before
it can react with ethanoic acid, CH3COOH.

Carbon Compounds 368

To prepare ethyl ethanoate SPM

’04/P3

Apparatus Figure 2.11 Preparation of ethyl ethanoate by reflux Activity 2.6 2

Round bottomed flask, Liebig condenser, oil bath, Observation
porcelain chips A colourless liquid with a fragrant odour is obtained.

Materials Conclusion
Ethyl ethanoate is produced when ethanoic acid and
Pure ethanol, glacial ethanoic acid and concentrated ethanol are heated in the presence of concentrated
sulphuric acid sulphuric acid as a catalyst.

Procedure CH3COOH + C2H5OH → CH3COOC2H5 + H2O
1 About 30 cm3 of pure ethanol and 25 cm3 of

glacial ethanoic acid are placed in a round bottom
flask. Small pieces of porcelain chips are added
to prevent bumping and to ensure smooth boiling.
2 About 5 cm3 of concentrated sulphuric acid is
added to the reaction mixture. The mixture is
shaken gently to ensure complete mixing.
3 The Liebig condenser is fitted vertically to the
round bottom flask. The mixture is boiled under
reflux for about 30 minutes.
4 After boiling, pure ethanol is obtained by
distillation.

Natural Sources of Esters 2.7

1 Most of the simple esters exist naturally 1 Name the following esters and identify the
in flowers and fruits. For example, pentyl alcohols and carboxylic acids required to prepare
ethanoate is found in bananas, octyl ethanoate these esters.
in lime and methyl butanoate in apples. (a) HCOOCH3
(b) CH3COOC3H7
2 These volatile esters are responsible for the (c) C3H7COOCH3
fragrant smell of flowers and fruits.
2 Name and draw the structural formulae of
3 Vegetable oils and animal fats are esters with the organic compounds produced from the
large molecules. For example, coconut oil and reactions between the following pairs of organic
palm oil. compounds.
(a) Methanol + propanoic acid
4 Waxes such as beeswax, wax found on leaves (b) Propan-1-ol + ethanoic acid
and candle wax are solid esters. (c) Propan-1-ol + methanoic acid

Uses of Esters in Daily Life 3 Methanol reacts with butanoic acid under certain
conditions to produce an ester.
To make perfumes, Used as solvents (a) Write a balanced equation for the reaction
cosmetics and artificial for many organic that occurs.
food flavourings compounds (b) State the conditions for the reaction that took
place.
Uses of esters (c) State two physical properties of the ester
produced.

To make Esters in oils Used as
synthetic medicine, for
polymers are used to example, aspirin
make soap

369 Carbon Compounds

2.8 Oils and Fats stearic acid is C17H35COOH or CH3(CH2)16COOH

1 Oils and fats are naturally occurring esters 2 A fatty acid with a carbon-carbon double bond is
and are found in animals and plants. SPM an unsaturated acid.
’08/P1 For example:
2 Fats (for example, butter) are found in animals.
Oils are usually found in plants and fish. OCHle3i(cCaHc2id)7CisHC1=7HC3H3C(OCHO2H)7CorOOH

3 Fats are solids at room temperature. In contrast The importance of oils and fats for body
oils are liquids at room temperature. Hence processes
fats have higher melting points than oils.
Sources of energy: Source of nutrients:
4 When fats and oils are hydrolysed, glycerol Fats are high energy Fats are required to
SPM and long chain carboxylic acids are formed. food, they provide enable the human
’08/P1 Hydrolysis means the decomposition (breaking energy for our body to absorb
bodies. vitamins A, D, E
up) of a chemical substance by water. and K

2 Ester + water → carboxylic acid + glycerol Importance of oils and
fats in our bodies
5 The carboxylic acids produced from fats are
also known as fatty acids. Fatty acids usually Thermal insulation: Protection:
contain 16 or 18 carbon atoms per molecule. The layer of fat The layer of fats
beneath the skin around the vital
6 Glycerol is an alcohol that contains three regulates body organs acts as a
hydroxyl (–OH) groups per molecule. temperature protective cushion

H H H Conversion of Unsaturated Fats to
| | | Saturated Fats

H—C—C—C—H 1 Vegetable oils can be converted to saturated
| | | fats by hydrogenation.
OH OH OH
2 Hydrogenation is the chemical process in
propane-1,2,3-triol (glycerol) which hydrogen is added to the double bond
between carbon atoms (C = C bond).
7 There are two types of carboxylic acids, namely,
saturated carboxylic acids and unsaturated 3 The hydrogenation process will change liquid
carboxylic acids. vegetable oils to solid fats.
(a) Saturated carboxylic acids do not contain
double bonds. 4 In the manufacture of margarine from
(b) Unsaturated carboxylic acids contain vegetable oil, hydrogenation is carried out by
double bonds. passing hydrogen gas into palm oil at 200 °C
and 4 atmospheres in the presence of nickel
8 Animal fats usually contain a high percentage powder as catalyst.
of saturated carboxylic acids whereas vegetable
oils and fish oil contain a high percentage of P alm oil + hydrogen ⎯20⎯0 °⎯CN,⎯i4 ⎯atm→
unsaturated carboxylic acids upon hydrolysis. margarine (fat)

9 Saturated fats are fats that contain saturated 5 The hardness of margarine formed depends
carboxylic acids. Unsaturated fats are fats that on the degree of hydrogenation. Partial
contain unsaturated carboxylic acids. hydrogenation will produce soft margarine.

10 The presence of double bonds in unsaturated
fats causes them to have lower melting points
than saturated fats. Hence unsaturated fats
(commonly known as oils) exist as liquids at
room temperature.

1 A fatty acid with the general formula of CnH2n+1COOH
is a saturated acid.
For example:
Palmitic acid is C15H31COOH or CH3(CH2)14COOH
and

Carbon Compounds 370

Effects of Eating Food High in Fats on 2.8
Health
1 State one similarity and one difference between
1 Food high in fats is high in calories. Hence fats and oils
high comsumption can lead to obesity. (a) in terms of their molecular structures.
(b) in terms of their physical properties.
2 Saturated fats contain a high percentage of
cholesterol. Excess intake of saturated fats 2 Stearic acid is a saturated fatty acid whereas oleic
increase the risk of acid is an unsaturated fatty acid.
(a) hypertension (high blood pressure) (a) Explain what is meant by a saturated fatty
(b) cardiovascular disease (heart disease) acid and an unsaturated fatty acid.
(c) stroke (b) Give a test to differentiate stearic acid from oleic
acid.
Industrial Extraction of Palm Oil
3 (a) Name the process in which palm oil is
1 There are two types of oil extracted from fresh converted to margarine.
oil palm fruits.
(a) Palm oil from the flesh of the fruit (b) State the conditions required for this conversion.
(b) Palm kernel oil from the kernel or seed (c) State one difference in physical property between

2 The flowchart shows the steps involved for the palm oil and margarine.
extraction of palm oil in the palm oil mill.
2.9 Natural Rubber 2

Sterilisation Fruit branches are sterilised to Natural Polymers
kill fungus and bacteria

Stripping Fruits are separated from the 1 Polymers can be classified into two broad
branches categories: natural polymers and synthetic
polymers.
Digestion Fruits are heated to break down
the oil-bearing cells 2 Examples of naturally-occurring polymers are

Pressing Oil is pressed out from fruits natural rubber, carbohydrates and proteins.
3 The monomer of natural rubber is isoprene,

C5H8. Hence natural rubber is polyisoprene.
Natural rubber is produced by the addition

polymerisation of isoprene.

Purification Mixture is filtered to separate the — H| C| H3 H| H — H) addition polymerisation
oil. Oil is then dried. C=C—C= |
n(H C ⎯⎯⎯⎯⎯⎯⎯⎯→

isoprene (monomer)

Advantage of palm oil as a vegetable oil H| C| H3 H| H
|

—( C ⎯ C = C ⎯ C —)n
| |

Rich in Vitamins Lower the LDL or bad H H
A and E cholesterol and raise the
HDL or good cholesterol in poly(isopropene) – natural rubber
the body
4 The monomers for carbohydrates such as
Advantage of palm oil as sugar, starch and cellulose is glucose.
a vegetable oil
When starch is heated with dilute acid, glucose is
produced. This reaction is called hydrolysis.

Withstand heat and Highly competive in – (C6H10O5)n– + nH2O → nC6H12O6
resistant to oxidation, price. starch glucose
hence suitable to be Cheaper than other
used for deep frying types of vegetable oils 5 The monomers of proteins are amino acids.
Amino acids are joined together by peptide
linkages. Hence proteins are polypeptides.

371 Carbon Compounds

Activity 2.7 2 Coagulation of Latex (a) the hydrogen ions from the acid neutralise
the negative charges on the membranes’
1 The milky fluid from tapped rubber trees is
called latex. surfaces of the colloidal particles.

2 The conversion of latex to the solid form is (b) When the neutral rubber particles collide,
known as coagulation.
the membranes will break, releasing the
3 Latex is a colloidal solution containing an
aqueous suspension of rubber particles. rubber polymers to form lumps. Hence

4 Each rubber particle contains rubber polymers the latex solidifies.
enclosed with a protein membrane with 8 The coagulation of latex can occur without the
negative charge.
addition of acid if the latex is exposed to air
5 The negative charge on the membrane’s surface
repel colloidal particles from one another, for a few days. This is because
preventing the rubber polymers from (a) the bacteria present in the latex produces
combining together. Hence the latex remains
in liquid form. organic acids.

6 Coagulation of rubber can be speeded up by (b) the hydrogen ions from the acids produced
the addition of acids.
neutralises the negative charges on the
7 The addition of a weak acid on latex causes
coagulation because rubber particles.
9 Coagulation of latex can be prevented by the

addition of aqueous ammonia because

(a) the hydroxide ions from aqueous ammonia
neutralise the acids produced by bacteria.

(b) the negative charges at the membranes of

rubber particles are maintained.

add a weak coagulation
acid of latex

• Latex is coagulated by adding a weak • The collisions between • The rubber polymers can
acid such as methanoic acid or ethanoic latex particles break coalesce (combine) and
acid. When an acid is added to latex, open the protein form lumps of rubber.
the hydrogen ions from the acid will membrane and releases This process of forming
neutralise the negative charges on the the rubber polymers. lumps of rubber is called
surfaces of the colloidal particles. coagulation of latex.
As a result, the particles become neutral
and can come closer and collide with • The lumps of rubber are
one another. white solids and are quite
elastic.

Figure 2.12 The coagulation of latex

To investigate the coagulation of latex and methods to SPM
prevent coagulation
’08/P3

Apparatus Procedure
Beaker, glass rod and dropper
1 About 50 cm3 of latex are placed in three beakers
Materials labelled A, B and C respectively.
Fresh latex, dilute ethanoic acid, dilute aqueous
ammonia and blue litmus paper. 2 Using a dropper, dilute ethanoic acid is added to
the latex in beaker B. The mixture is stirred with
a glass rod until the latex becomes acidic (blue
litmus paper turns red).

Carbon Compounds 372

3 Aqueous ammonia is slowly added to beaker Beaker Chemicals added Observation
C until the latex becomes alkaline (red litmus to latex
paper turns blue).
B Latex + acid Coagulation of latex
4 The three beakers are left overnight. The changes occurs rapidly
that occurred are recorded.

C Latex + aqueous Latex does not

ammonia coagulate (no visible

changes)

Figure 2.13 To investigate the coagulation of latex Conclusion
Results
1 Acids such as ethanoic acid speed up the
coagulation of latex.

2 Alkalis such as aqueous ammonia slow down the
coagulation of latex.

3 Coagulation of latex can occur by itself slowly.

Beaker Chemicals added Observation
to latex
Coagulation occurs
A Latex only slowly

2

Properties of Natural Unvulcanised SPM 6 Vulcanisation is the process of hardening

Rubber and Vulcanised Rubber ’10/P1 rubber by heating it with sulphur or sulphur

compounds.

1 Natural rubber has the following properties: 7 Vulcanisation of rubber is carried out by
(a) Quite elastic
(a) heating natural rubber with sulphur at
(b) Water repellent
about 140 °C, using zinc oxide as catalyst,
(c) Does not conduct electricity
2 Elasticity is the ability of an object to be (b) immersing rubber in a solution of disulphur

stretched and then returned to its original 8 In dichloride (S2Cl2) in methylbenzene.
vulcanised rubber, the sulphur atoms form
shape when the stress is removed.
3 Natural rubber before treatment with sulphur cross-links between long chains of rubber

is unvulcanised rubber. polymers.
4 Unvulcanised natural rubber has few practical
c rubber polymer c
uses because s s
(a) it is not elastic enough s s sulphur
(b) it becomes soft and sticky when heated c c c cross-links TC 2/15
(c) it becomes brittle and crack easily when s
s
oxidised by oxygen. c cc
5 When unvulcanised rubber is stretched, the
Figure 2.15 Vulcanised rubber has sulphur cross-links
coiled rubber molecule is lengthened and
straightened. 9 Vulcanised rubber has many uses because

of improved properties. Vulcanisation makes
the rubber more elastic, stronger and more
resistant to heat and oxidation.

Improved properties of Explanation
vulcanised rubber

Stronger and harder The sulphur cross-links
prevent the polymer
polymer chain of rubber polymer chain of rubber chains from slipping
under ordinary conditions when straightened
past one another when
Figure 2.14 Unvulcanised rubber is not very elastic
stretched

373 Carbon Compounds

Improved properties of Explanation Improved properties of Explanation
vulcanised rubber vulcanised rubber

More elastic The sulphur cross-links More resistant to Sulphur cross-links
pull the chains back to oxygen reduce the number of
their original arrangement double bonds in the
when released molecules of vulcanised
rubber
More resistant to heat The presence of sulphur
increases the melting
point of rubber

To produce vulcanised rubber and to compare the properties
of vulcanised rubber and unvulcanised natural rubber

(A) Preparation of natural rubber and vulcanised Materials
rubber
Vulcanised rubber and unvulcanised rubber.
Activity 2.8 2 Apparatus
Glass plate, beaker, a pair of tongs and razor blade. Procedure

Materials 1 A strip of vulcanised rubber is hung using a clip.
2 The original length of the vulcanised rubber strip
Disulphur dichloride in methylbenzene and rubber
latex. is measured.
3 A 20 g weight is hung on the strip of vulcanised
Procedure
rubber.
1 A small quantity of latex is poured on a glass plate. 4 The increase in length of the vulcanised rubber strip
2 A glass rod is used to level the latex to produce a
is measured.
flat, thin layer of latex about 1 mm thick. 5 The weight is removed and the final length of the
3 The glass plate is put aside for one day for the
vulcanised rubber strip is measured again.
latex to coagulate. 6 Steps 1 to 5 are repeated using the unvulcanised
4 The rubber produced is cut into two strips of
rubber strip of the same length to replace the
rubber of equal size using a razor blade. vulcanised rubber strip.
5 One of the strips of rubber is dipped into a solution
UHWRUW VWDQG FOLS
of disulphur dichloride in methylbenzene for 2-3 UXEEHU VWULS
minutes to produce a strip of vulcanised rubber.
6 The strip of vulcanised rubber is then removed UXOHU WKUHDG
from the solution and dried with filter paper. J ZHLJKW

(B) To compare the elasticity of vulcanised rubber
and unvulcanised rubber

Apparatus SPM
Clip, retort stand with clamp, metre rule and
weight. ’06/P3

Results Figure 2.16 To compare the elasticity of rubber

Type of rubber Original length Stretched length Increase in length Final length after
(cm) with weight (cm) (cm) weight is removed
Unvulcanised
rubber X X1 (cm)
Vulcanised rubber X2
X X1 – X = Y1 Y3
X2 – X = Y2 Y4

Carbon Compounds 374

Discussion is taken off (that is Y4 < Y3). This shows that
the vulcanised rubber is more elastic than
1 The increase in length of vulcanised rubber unvulcanised rubber.
(stretched length) is less than the increase in
length of unvulcanised rubber (that is, Y2 < Y1). Conclusion
This shows that vulcanised rubber is harder and Vulcanised rubber is harder, stronger and more
stronger than unvulcanised rubber. elastic than unvulcanised rubber.

2 The vulcanised rubber has a higher ability to
return to its original length after the weight

Uses of Natural Rubber 2 Unvulcanised natural rubber is used for
making adhesive (glue) and as crepe rubber in
1 Unvulcanised natural rubber has limited uses insulating blankets.
as it is soft, has poor heat resistance and does
not wear well. It becomes soft and sticky when 3 Vulcanised rubber has many uses in industries
heated. It also becomes hard and brittle due and home.
to oxidation.

Vehicle tyres Surgical gloves and Shoe soles
protective gloves
2

Shock absorbers Things Rubber hoses
made from Rubber bands
Insulating layer for electric vulcanised
cables and equipment natural
rubber
Conveyor belts
Rubber mattresses
Balloons

Research on Natural Rubber in Malaysia 2 The scope of research and development activities
include
1 In Malaysia, the research and development on (a) finding new uses of rubber and rubber
rubber is conducted by the products
(a) Rubber Research Institute of Malaysia (b) improving the quality of natural rubber
(RRIM) (c) automating the tapping system so as to
(b) Malaysian Rubber Producer Research overcome labour shortage.
Association (MRPRA)
(c) Rubber Board of Malaysia

375 Carbon Compounds

2.9 2.11 The Variety of Organic
Materials in Nature
1 Complete the following table.

Natural polymer Monomer Uses of Various Organic Materials in
Protein Isoprene Everyday Life

Carbohydrate 1 Organic compounds were originally extracted
Starch from living things, products or remains of
living things. The term organic actually means
2 State the chemicals used in the following processes ‘derived from living organisms’. Living things
in rubber industries and their effects on the are made of complex organic compounds that
properties of rubber. have structural, chemical or genetic functions.
(a) Coagulation
(b) Vulcanisation 2 However since the nineteenth century, organic
compounds have been synthesised in the
3 What causes latex to coagulate under natural laboratory from inorganic materials. In 1828,
conditions? Suggest a method to prevent this the German chemist Friedrich Wohler was able
phenomenon. to synthesise urea (an organic compound)
from ammonium cyanate (an inorganic
2 compound).

2.10 Order in Homologous 3 In present times, thousands of organic
Series compounds are synthesised every year to
fulfill our needs in the modern society.
1 Organic compounds are grouped in families These synthetic organic compounds include
synthetic polymers, vitamins, medicines,
called the homologous series to make the cosmetics, pesticides, paints, varnishes,
study of organic chemistry more systematic glues, adhesives, synthetic fibers for clothing
and orderly. materials and others.
2 Alkanes, alkenes, alcohols, carboxylic acids and
4 Organic synthesis is the preparation of
esters are examples of homologous series. specific and desired organic compounds from
3 The chemical properties of members of a readily available resources.

homologous series are the same as they have 5 Research and development towards natural
organic compounds enable us to
the same functional group. (a) simulate the structure of natural organic
4 The physical properties of members of a compounds and make useful synthetic
organic compounds which are imitations
homologous series show a regular pattern of natural compounds. Examples: Dyes,
and change gradually as the number of food flavours, fragrances and medicines.
(b) extract the active ingredients from
carbon atoms increases. traditional medicines. Cheaper and more
effective medicines without side effects
Descending the • Relative molecular can then be made commercially. Generic
homologous mass increases medicines are made to lower the cost of
series as the medicines for consumers.
number of • Melting point (c) produce seeds of higher quality and more
increases resistant towards pests, so as to increase
carbon atoms the yield of food production.
• Boiling point (d) find new uses for agriculture products.
increases increases For example, oil palm waste is used to
produce biomass fuel and make composite
• Volatility decreases construction materials.

• Density increases 6 The economical development of our country
depends heavily on products of organic
• Solubility decreases

5 The order in the physical properties of members
in a homologous series enables us to predict
the properties of an unknown member in the
series.

Carbon Compounds 376

compounds such as petroleum, palm oil and 8 In 2012, universities and research institutes in
natural rubber. collaboration with Agensi Innovasi Malaysia
7 Presently, research and development of natural have successfully developed products such as
resources in our country is encouraged to disease-resistant chilli, lumber from oil palm,
produce new and useful organic compounds. coconut body armour, biopesticide to control
New synthetic medicines are developed mosquito larvae and mosquito repellant gel.
to combat disease and new polymers are
synthesised to replace the use of metals and
even replace organs in our bodies.

1 Organic carbon compounds include hydrocarbons (b) Hydrolysis of ethene (phosphoric acid as a 2
such as alkanes and alkenes, alcohols, carboxylic catalyst)
acids, esters, fats and oils and natural rubber.
7 Chemical properties of carboxylic acids (general
2 Physical properties of alkanes and alkenes: formula: CnH2n+1COOH):
(a) Low melting and boiling points (a) Reacts with reactive metals to form salts and H2
(b) Insoluble in water, soluble in organic solvents gas
(c) Non-conductors of electricity (b) Reacts with metal carbonates to form salts and
CO2 gas
3 Chemical properties of alkanes (general formula: (c) Reacts with alkalis to form salts and H2O
CnH2n+2): (d) Esterification with alcohols to form esters and
(a) Combustion in excess oxygen to form CO2 and H2O
H2O
(b) Substitution reactions with halogen under 8 Physical properties of esters (general formula:
ultraviolet light RCOOR′):
(a) Have sweet/ fragrant/ fruity smells
4 Chemical properties of alkenes (general formula: (b) Insoluble in water
CnH2n):
(a) Combustion in excess oxygen to form CO2 and 9 Fats and oils are esters.
H2O (a) Fats are solids (with lower melting points) and
(b) Addition reaction are saturated (without C = C bonds).
(i) with H2 (hydrogenation) to form alkanes (b) Oils are liquids (with higher melting points) and
(ii) with H2O (hydrolysis) to form alcohols are unsaturated (with C = C bonds).
(iii) with KMnO4 to form diols (c) Oils can be converted to margarine by
(iv) with Cl2 or Br2 to form dichloroalkanes or hydrogenation.
dibromoalkanes
(c) Polymerisation to form polymers 10 Hydrolysis of fats (or oils) will produced fatty acids
(long chained carboxylic acids) and glycerol.
5 Chemical properties of alcohols (general formula:
CnH2n+1OH): 11 Coagulation is the conversion of liquid latex to
(a) Combustion in excess oxygen to form CO2 and rubber solid. It
H2O (a) can be speeded by the addition of acids.
(b) Oxidation by acidified KMnO4 or K2Cr2O7 to form (b) can occur slowly when the bacteria present
carboxylic acids produce acids.
(c) Dehydration by heated porcelain to form (c) can be prevented by the addition of aqueous
alkenes ammonia.
(d) Esterification with carboxylic acids (with conc.
H2SO4 as a catalyst) to form esters 12 Vulcanisation of rubber is the conversion of natural
rubber to vulcanised rubber by forming sulphur
6 Preparation of ethanol, C2H5OH: cross-links between rubber polymers. Vulcanised
(a) Fermentation of glucose by yeast rubber is stronger, harder, more elastic and more
resistant to heat and oxidation.

377 Carbon Compounds

2

Multiple-choice Questions

2.1 Carbon Compounds 6 Which of the following produces 9 Propene can be transformed to
propane by the process of
1 Which of the following is an the most soot when burned in air?
organic compound? A Methane ’07 A hydration
A Calcium carbonate B Ethane B oxidation
B Glucose C Butane C dehydration
C Carbon monoxide D Hexane D hydrogenation
D Copper(II) oxide
10 A hydrocarbon compound is
2 2 Which of the following products 2.3 Alkenes burnt completely in air to form
are formed from the complete
combustion of all organic 7 Which of the following ’05 7.2 cm3 of carbon dioxide gas
compounds? substances can be used to and 7.2 cm3 of water vapour.
A Water and carbon dioxide What is the molecular formula
B Carbon dioxide and carbon ’04 differentiate propene from of the hydrocarbon compound?
monoxide propane? [Given that 1 mol of gas
C Water, carbon dioxide and A Limewater occupies 24 dm3 at room
nitrogen dioxide B Bromine water temperature]
D Carbon and water C Sodium hydroxide solution ACDB CCCC6233HHHH6866
D Potassium dichromate(VI)
2.2 Alkanes solution 11 What is the product formed
when propene is shaken with
3 Which of the following is a 8 Which of the following is
saturated hydrocarbon? the structural formula of an ’10 chlorine water?
A 1, 1- dichloropropane
’06 A Alkane ’05 unsaturated hydrocarbon? B 2, 2 -dichloropropane
B Alkene C 1, 2- dichloropropane
C Alcohol H H H H D 1, 3- dichloropropane
D Carboxylic acid | | | |
A H — C — C = C — C — H 12 The diagram below shows
4 Which of the following substances | | the structural formula of a
can undergo substitution reaction H H
’11 compound.
’06 with chlorine in sunlight? H H H H
A Ethane | | | |
B Ethene B H — C — C = C — C — H H
C Ethanol | | |
D Ethanoic acid H OH H—C—H
H H H
5 What are the products formed H O | | |
when ethane is burnt with | i
C H — C — C — O — H H—C=C—C—C—H
’07 excess oxygen? | | |
A Carbon and hydrogen H H H
B Carbon dioxide and water
C Carbon monoxide and water H H H H What is the name of this
D Carbon monoxide and | | | | compound?
hydrogen D H — C — C — C — C — H A Pentene
| | | | B Methylbutene
H H H H C 2-methylbut-1-ene
D 2-methylbut-2-ene

Carbon Compounds 378

13 Polypropene is a polymer that A Pentane H
is formed from the combination B Methylbutane |
C 2-methylbutane H—C—H
’07 of propene molecules. Which of D 3-methylbutane H H
the following represents part of | |
the structure of polypropene? 16 Which of the following pairs of
compounds are isomers? H—C—C=C—H
H H H H A Butane and butene |
| | | | B Butane and 2-methylbutane H
A — C — C — C — C — C But-1-ene and
| | | | 2-methylpropene What is the name of the
H H H H D 2,2-dimethyl propane and compound formed when
2-methylpropane compound X reacts with
H C| H3 H| C| H3 potassium permanganate?
| 2.5 Alcohols A Butanol
B — C — C — C — C — 17 The diagram shows the set-up B 2-methylpropanol
| | | | C Butan-1,2-diol
H H H H of apparatus for the reaction of D 2-methylpropan-1,2-diol
’06 yeast with glucose solution.
H C| H3 H| H 20 The diagram below shows
| | What is the name of the reaction the structural formula of
C — C — C — C — C — that has taken place in the conical
| | | | flask after a few days? ’04 pent-1-ene.
H CH3 H H A Oxidation
B Hydration H H H H H 2
C Hydrolysis | | | | |
C| H3 H| H H D Fermentation H—C=C—C—C—C—H
| | | | |
D — C — C — C — C — 18 The following chemical equation H H H
| | | | shows the conversion of ethanol
H H H H Which of the following are
’04 to ethanoic acid. the possible alcohols that
2.4 Isomerism C2H5OH + 2[O] → can produce pent-1-ene on
CH3COOH + H2O dehydration?
14 Which of the following is What is the name of the process I Pentan-1-ol
true of all the isomers of a shown by the above equation? II Pentan-2-ol
hydrocarbon? A Dehydration III Pentan-3-ol
A They have the same structural B Reduction IV 2-methylbutan-1-ol
formula. C Oxidation A I and II only
B They have the same functional D Fermentation B II and IV only
group. C I and IV only
C They have the same chemical 19 The diagram shows the structural D I, II and III only
properties. formula of compound X.
D They produce the same 21 The diagram below shows the
number of moles of carbon set-up of the apparatus for a
dioxide and water on
complete combustion. ’05 reaction.

15 The structural formula of a glass wool porcelain compound X
compound is given below. soaked with chips
ethanol
’05 H
| heat heat
H—C—H
H H H water
| | |
H—C—C—C—C—H Which of the following is
| | | |
H H H H compound X?
Which of the following is the
IUPAC name for the compound? A Ethane TC 2/18
B Ethene

C Ethanoic acid

D Carbon dioxide

379 Carbon Compounds

22 C| H3 Glucose Which of the following is the
fermentation structural formula for compound
Z?
H3C – C – OH O
| i
H
X A C2H5 — C — O — CH3
Which of the following may oxidation
be true of the compound
Y O
represented in the figure i

above? Which of the following pairs of B CH3 — C — O — C3H7
A Decolourise the brown colour compounds may be compound
X and compound Y?
of bromine water. O
B Decolourise the purple colour i

of cold aqueous potassium XY C C2H5 — C — O — C2H5

permanganate. A Ethanol Ethanoic acid
C Changes the orange colour B Ethanol Ethene O
i
of potassium dichromate to
C Propanol Propanoic acid D C2H5 — C — O — C3H7
green when heated.
D Produces a sweet-smelling D Yeast Carbon dioxide

liquid when heated with

ethanol and concentrated

sulphuric acid.

2 2.7 Esters 29 Which of the following equations
can produce a product with a
2.6 Carboxylic Acids 26 Scented flowers contain naturally
occurring esters. Which of the ’06 sweet fruity scent?
23 Compound X has the following
properties: ’04 following is a property of an I CH3COOH + NaOH →
ester? CH3COONa + H2O
• Reacts with sodium carbonate A Soluble in water
to produce a gas that turns B Low boiling point II CH3OH + C2H5COOH →
limewater milky. C Higher density than water C2H5COOCH3 + H2O
D Change blue litmus to red
• Reacts with ethanol to III C2H5OH + 2[O] →
produce a sweet-smelling 27 The diagram below represents CH3COOH + H2O
compound. the structural formula of a
IV C5H11OH + CH3COOH →
Which of the following ’04 carbon compound. CH3COOC5H11 + H2O
compounds may be compound
X? O A I and III only
A Carbonic acid i B II and IV only
B Ethanoic acid CH3 — CH2 — C — O — CH2 — CH2 — CH2 — CH3 C III and IV only
C Propanol D I, II and IV only
D Ethyl ethanoate The compound is produced by
the reaction between 30 The diagram shows the
A ethanol and butanoic acid conversion of ethanol to
24 A liquid produced effervescence B butanol and ethanoic acid compound X and subsequently
when reacted with zinc metal. C butanol and propanoic acid to compound Y.
D propanol and butanoic acid
’05 Which of the following may be ⎯a⎯cid⎯ifie⎯d ⎯KM⎯nO→4 X
the molecular formula of the 28 The diagram below shows the C2H5OH
liquid? process of producing compound
A HCOOH ⎯C⎯H3⎯OHH2⎯S,Oc⎯o4,n⎯rceef⎯lnutxr⎯ate⎯d → Y
’05 Z.
CDB CCHHHCO33OCOOHCOHN3a
C3H6
25 The diagram shows the
conversion of glucose to + steam
compound X and subsequently
to compound Y. Ethanol + Y X Which of the following may be
C2H5OH oxidation
compound Y?
Compound Z A Ethanoic acid
B Ethyl ethanoate
C Ethyl methanoate
D Methyl ethanoate

Carbon Compounds 380

2.8 Oils and Fats A I only C I, II and III only
B III only D I, II, III and IV
31 Which of the following belong
to the homologous series of 34 The diagram shows the change in structure of natural rubber after process
esters? P.

I Palm oil cc cc process P c c css
II Margarine c c c c cc s s c
III Sodium butanoate s cs c c
IV Glycerol cc cc c

A I and II only rubber X rubber Y
B I and III only
C III and IV only Which of the following statements is true about the change?
D I, II and III only
A Rubber X is more elastic than rubber Y.
32 Which of the following molecular B Rubber X is stronger than rubbeTrCY.2/19
formulae of fatty acids is formed C Rubber X is more resistant to heat than rubber Y.
from the hydrolysis of a non- D Rubber X is more easily oxidised than rubber Y.
saturated fat?
DCBA CCCC11127753HHHH33345137CCCCOOOOOOOOHHHH 35 A rubber tapper faces a problem of transporting latex to a glove-making 2
factory in liquid form. To solve the problem he has to add a substance
2.9 Natural Rubber
’06 into the latex to prevent the coagulation of the latex.
33 Which of the following chemicals Choose the correct substance and the explanation to solve the problem.
can cause latex to coagulate?
Substance Explanation
I Methanoic acid
II Sulphuric acid A Water To make the latex more dilute
III Ethanoic acid
IV Nitric acid B Ethanoic acid Contains H+ ions that neutralise the negative
charge on the membrane of the rubber particle

C Ammonia Contains OH– ions that neutralise the H+ ions
solution from the acids produced by bacteria

D Sodium chloride As a preservative to maintain the original state of

solution the latex

Structured Questions

1 Table 1 shows the names, molecular formulae, melting (b) Complete Table 1 by filling in the molecular
points and boiling points of a few straight chain
members of a homologous series. formula of propane and the name of C4H10.
[2 marks]

Molecular Melting Boiling (c) Draw the structural formula of the first member

Name formula point (°C) point (°C) of this homologous series. [1 mark]

Ethane C2H6 –183 –89 (d) Predict the physical states of [1 mark]
Propane –188 –42 (i) propane [1 mark]

(ii) pentane

Pentane C4H10 –138 –0.5 (e) Give the name and the molecular formula of the
C5H12 –130 36 member of the same homologous series after
pentane. [2 marks]

(f) Write a balanced equation for the complete

Table 1 combustion of ethane. [1 mark]

(a) Give the name and the general formula of this

homologous series. [2 marks]

381 Carbon Compounds

2 Propene is an important hydrocarbon in the petrochemical (b) State the function of concentrated sulphuric acid
industries. Diagram 1 shows the conversion of propene
into other organic compounds. in this reaction. [1 mark]

(c) (i) Name the reaction for the preparation of

Polypropene ethyl ethanoate. [1 mark]

(ii) Write the chemical reaction for the reaction

process II in (i). [1 mark]

process process (d) The experiment is repeated by replacing ethanol
I III
Propane Propene Propan-1-ol with methanol.

(i) Name the ester formed. [1 mark]

process IV (ii) Draw the structural formula of the ester

formed. [1 mark]

Compound X (iii) State one physical property of the ester.

Diagram 1 [1 mark]

Based on Diagram 1, answer the following questions. (e) The flowchart shows the conversion of ethene to
ethanol and then to ethanoic acid.

(a) State the homologous series of propene.

[1 mark] Ethene process I Ethanol process II Ethanoic
acid
(b) Name process I. [1 mark]

(c) Under certain conditions, propene reacts to form

polypropene. Write an equation for the formation Based on the flowchart, write the chemical

2 of polypropene in process II. [1 mark] equation for

(d) (i) Explain briefly how process III is carried out (i) process I [1 mark]

in industries. [2 marks] (ii) process II [1 mark]

(ii) Draw the structural formula of propan-1-ol. (iii) State a suitable chemical that can be used

[1 mark] to carry out process II. [1 mark]

(e) Acidified potassium manganate(VII) is added to 4 Diagram 3 shows conversions I, II and III starting with
propene in process IV. glucose.

(i) Predict the observation that will take place.

[1 mark]

(ii) Write a balanced equation for the reaction Glucose I Liquid II Liquid
yeast A reagent B
that has occurred. [1 mark]

(f) Both propene and propane are combustible in

air. Compare and explain the difference in the III concentrated
H2SO4 asid
quantity of soot produced by the two compounds

during combustion. [2 marks] Liquid C

3 Diagram 2 shows the set-up of apparatus for the Diagram 3
preparation of ethyl ethanoate by heating ethanol
and ethanoic acid under reflux. (a) (i) Name conversion I. [1 mark]

(ii) Draw the structural formula of liquid A.

[1 mark]

water out (b) Liquid B has a vinegary smell.

(i) Name the type of reaction that takes place

in conversion II. [1 mark]

(ii) Write a chemical equation for conversion II.

water in TC 2/20 [1 mark]

(c) Give one chemical test that can be used to

ethanol, ethanoic acid distinguish liquid B from liquid A. [2 marks]
and concentrated
sulphuric acid (d) (i) Name the homologous series of which

xxxxxxxxxxxxxx liquid C is a member. [1 mark]

heat (ii) Name liquid C. [1 mark]

(iii) State one use of liquid C. [1 mark]

Diagram 2 (e) Suggest another method to produce liquid A

(a) Why is ethanol and ethanoic acid heated under other than from glucose in conversion I.

reflux? [1 mark] [1 mark]

Carbon Compounds 382

5 Diagram 4 shows the conversion of latex to compound (c) Name compound X. [1 mark]
X.
(d) State two differences in physical properties
c c between natural rubber and compound X.
s s
Latex process I Natural process II s s [2 marks]
rubber c c c TC 2/21
s
s (e) How is process II carried out in the industry?
c cc
[1 mark]

compound X (f) (i) Name a chemical that can be used to retain

Diagram 4 latex in the liquid form. [1 mark]

(a) Name process I and process II. [2 marks] (ii) Explain the function of the chemical named

in (i). [1 mark]

(b) Name a chemical that can be used to carry out (g) Give one use of compound X. [1 mark]

process I. [1 mark]

Essay Questions

1 (a) Draw the structural formulae of two isomers of 2 (a) Diagram 1 shows the formation of carboxylic acids
but-1-ene and give their IUPAC names. [4 marks] from alcohols.

(b) The information below is referring to carbon Alcohols Carboxylic acids
compound X.
Diagram 1 2
• Carbon 40.0%
• Hydrogen 6.7% Using suitable reagents and with the help of a
• Oxygen 53.3% labelled diagram, describe how you can prepare
• Relative molecular mass = 60 a named carboxylic acid in the laboratory.
• Relative atomic mass of H = 1, C = 12 Include the observation and a test to show that
the product formed is an acid. Write a chemical
and O = 16 equation for the reaction involved.
[10 marks]
Based on the information of the carbon compound

X, (b) Many artificial flavours used in the food industry
are esters. Various types of esters can be formed
(i) determine the molecular formula of X. from the esterification between an alcohol and a
carboxylic acid. Name one possible ester that can
(ii) draw the structural formula of X. be formed and describe how you can prepare
the named ester in the laboratory. Name the
(iii) name the carbon compound X. alcohol and carboxylic acid that is used and the
chemical equations involved.
(iv) write the general formula for its homologous

series. [8 marks]

(c) Margarine can be made from palm oil. Compare

and contrast margarine and palm oil in terms of

their structures and physical properties. Briefly [10 marks]

describe how palm oil can be converted to

margarine. [8 marks]

Experiment Your planning should include the following:

1 Hexane is a saturated hydrocarbon whereas hexene (i) Statement of the problem
is an unsaturated hydrocarbon. Both are colourless
liquids. However they undergo different reactions (ii) All the variables
toward addition reaction.
(iii) Hypothesis
You are required to plan an experiment to differentiate
the two compounds. (iv) List of materials and apparatus

(v) Procedure

(vi) Tabulation of data [17 marks]

383 Carbon Compounds

3CHAPTER FORM 5

THEME: Interaction between Chemicals

Oxidation and Reduction

SPM Topical Analysis

Year 2008 2009 2010 2011
Paper 123 123 123 123
Section
ABC ABC ABC ABC
Number of questions 5 —1 – 1 –
4 ––1 – 4 ––– – 3 1–– –
6

ONCEPT MAP

Oxidising agent Reducing agent
A substance that accepts (gains) electrons and is itself A substance that donates (loses) electrons and is itself
reduced in the process oxidised in the process

Oxidation Reduction
• Gain of oxygen/increase in oxidation number • Loss of oxygen/decrease in oxidation number
• Loss of hydrogen/loss of electrons • Gain of hydrogen/gain of electrons

Rusting of iron OXIDATION- Displacement of halogens from
Fe → Fe2+ + 2e– → Fe2O3.xH2O REDUCTION (REDOX) the halides

Oxidation of Fe2+ ions: REACTIONS e.g. Cl2 + 2KBr → 2KCl + Br2
Fe2+ → Fe3+ + e–
Reduction of Fe3+ ions:
Fe3+ + e– → Fe2+

Combustion of metals Displacement of metals from their salts Heating metal oxides with
e.g. Zn + CuSO4 → ZnSO4 + Cu carbon and hydrogen

Reactivity series of metals Electrochemical series Position of C and H in the reactivity
K > Na > Ca > Mg > Al > Zn > Fe > K > Na > Ca > Mg > Al > Zn > Fe > series of metals
Sn > Pb > Cu > Ag > Au Sn > Pb > H > Cu > Ag K > Na > Ca > Mg > Al > C > Zn > H

> Fe > Sn > Pb > Cu > Ag

Prevention of rusting Electrolytic cell • Extraction of iron
• Galvanising • Electrons flow from anode (+ve) to 2Fe2O3 + 3C → 4Fe + 3CO2
• Sacrificial metal
• Alloying cathode (–ve) in the external circuit • Extraction of tin
SnO2 + C → Sn + CO2

Chemical cell
• Electrons flow from anode (–ve) to cathode (+ve) in the external circuit

3.1 Redox Reactions Oxidation in Terms of Loss of Hydrogen

Oxidation and Reduction Reactions SPM 1 Oxidation can also be defined as the loss of
1 Oxidation can be defined as hydrogen from a substance. If a substance
’08/P1, loses hydrogen during a reaction, it is said
’09/P1 to be oxidised.

(a) acceptance (gain) of oxygen, 2 When hydrogen sulphide gas is mixed with
chlorine gas at room temperature, a yellow
(b) donation (loss) of hydrogen, precipitate of sulphur is formed and hydrogen
chloride gas is released.
(c) loss of electrons and,
H2S(g) + Cl2(g) → 2HCl(g) + S(s)
(d) increase in the oxidation number of the

element. loss of hydrogen
(oxidation)
2 In contrast, reduction can be defined as
In this reaction, hydrogen sulphide loses
(a) loss of oxygen, hydrogen and is oxidised to sulphur.

(b) gain of hydrogen, 3 When ammonia gas is passed over hot
copper(II) oxide, the following reaction occurs.
(c) gain of electrons and,
2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(l)
(d) decrease in the oxidation number of the

element. oxidation

A newly cut apple turns yellow on exposure to air. This Ammonia undergoes oxidation because it 3
is due to the oxidation of apples by oxygen. The reaction loses hydrogen. In other words, ammonia is
is catalysed by the enzymes present in apples. oxidised to nitrogen.

Oxidation in Terms of Gain of Oxygen Reduction in Terms of Loss of Oxygen

1 Oxidation is a chemical reaction in which 1 A reduction reaction is the reverse process of
oxygen is added to a substance. If a substance an oxidation reaction. Reduction is defined
(element or compound) gains oxygen during as the loss of oxygen from a substance. If a
a reaction, it is said to be oxidised. substance loses oxygen during a reaction, it
is said to be reduced.
2 When calcium burns in oxygen, the following
reaction occurs: 2 When a mixture of zinc powder and
copper(II) oxide is heated, the following
2Ca(s) + O2(g) → 2CaO(s) reaction occurs.

loss of oxygen
addition of oxygen (reduction)
(oxidation)

(a) This process is known as oxidation. Zn(s) + CuO(s) → ZnO(s) + Cu(s)
(b) Calcium is oxidised to calcium oxide
3 In this reaction, copper(II) oxide has lost its
because it gains oxygen in this reaction. oxygen. It is said to be reduced to metallic
3 Methane burns in air as represented by the
copper.
equation:
oxidation

CH4(g) + 2O2(g) ⎯⎯⎯→ CO2(g) + 2H2O(g)
oxidation

In this reaction,
(a) the carbon atom in methane is oxidised

to carbon dioxide,
(b) the hydrogen atoms in methane is oxidised

to water.
Therefore, combustion is an oxidation reaction.

385 Oxidation and Reduction

Reduction in Terms of Gain of Hydrogen oxidation

1 Reduction can also be defined as the addition Mg(s) + H2O(g) → MgO(s) + H2(g)
of hydrogen to a substance. If a substance
gains hydrogen during a reaction, it is said reduction
to be reduced. 4 In this reaction, magnesium has gained oxygen

2 When a mixture of hydrogen and chlorine and is oxidised. In contrast, water has lost its
is exposed to sunlight, a vigorous reaction oxygen and is reduced.
occurs and white fumes of hydrogen chloride
are produced. Respiration is a redox process. When respiration occurs,
the food is oxidised and oxygen molecules accept
addition of hydrogen electrons and are reduced to water. Photosynthesis is
(reduction) also a redox reaction.

6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)
H2(g) + Cl2(g) → 2HCl(g) sugar
Electrons are removed from water molecules and are
3 In this reaction, chlorine has gained used to reduce carbon dioxide to sugar.
hydrogen. This means that chlorine has
been reduced.

3

Oxidising and Reducing Agents SPM

’08/P1,
’09/P1

Antoine Lavoisier (1743–1794) 1 An oxidising agent is a substance that brings

Antoine Lavoisier is known as the Father of Modern about (causes) oxidation in another substance.
Chemistry. He was the first chemist who explained the
oxidation and reduction reactions that occur during In bringing about oxidation, the oxidising
combustion. agent is itself reduced.
2 A reducing agent is a substance that brings
Redox Reactions
about reduction in another substance and is
1 Oxidation and reduction always take place itself oxidised.
together. A redox reaction is defined as a reaction 3 The following are examples of oxidising and
in which both oxidation and reduction take place
simultaneously. reducing agents.

2 In a redox reaction, when one substance in Oxidising agents Reducing agents
a reaction is oxidised, the other substance is
reduced. • Chlorine and • Metals such as
bromine sodium, magnesium,
3 When steam is passed over heated magnesium, zinc and aluminium
magnesium oxide and hydrogen are produced. • Acidified potassium
manganate(VII) • Sulphur dioxide gas
and hydrogen
• Acidified potassium sulphide gas
dichromate(VI)
• Sodium sulphite and
• Concentrated nitric sodium thiosulphate
acid

4 In a redox reaction involving A and B: if A
is an oxidising agent, then B is the reducing
agent and vice versa.

Oxidation and Reduction 386

Reaction Oxidising agent Reducing agent

The reaction between copper(II) oxide and carbon: Copper(II) oxide Carbon
• Copper(II) oxide • Carbon reduces
oxidised
(gain oxygen) oxidises carbon to copper(II) oxide to
carbon dioxide. copper.
• It is reduced to copper. • It is oxidised to carbon
2CuO(s) + C(s) → 2Cu(s) + CO2(g) dioxide.


reduced
(loss of oxygen)

The reaction between chlorine and hydrogen sulphide: Chlorine Hydrogen sulphide
• Chlorine oxidises • Hydrogen sulphide
oxidised
(loss of hydrogen) hydrogen sulphide to reduces chlorine to
sulphur. hydrogen chloride.
• It is reduced to • It is oxidised to
Cl2(g) + H2S(g) → 2HCl(g) + S(s) hydrogen chloride. sulphur.

3
reduced
(gain hydrogen)

1 In many cases, oxidation or reduction reactions are
accompanied by colour changes.
The equation for the reaction between iron(III) MCBFerrn222(O+Ob7(4r2–go–(r(wpeonuera)rnpn)→lge→e))B→Fr→–e(3Mc+Conrl(o32b++uror((lgewcorsneslo/e)yun…er)llelo…srwse)d)reu……dctuirocoetnxidoidunacttiioonn
oxide and carbon monoxide is shown below. 2I– (colourless) → I2(brown) … oxidation

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) Methylhydrazine, CH3NHNH2 is a powerful reducing
Identify the oxidising and reducing agents in this agent.
reaction.
4CH3NHNH2 + 5N2O4 → 4CO2 + 9N2 + 12H2O
Solution
It is used as rocket fuel for the Apollo 11 project which
Fe2O3 is an oxidising agent because it oxidises landed the first man on the moon on 21 July 1969.
CO to CO2 and is itself reduced to Fe. The compound is toxic and carcinogenic (cancer causing).
It is also found in trace amounts in raw common
oxidation mushrooms.


Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

reduction

CO is a reducing agent because it reduces
Fe2O3 to Fe and is itself oxidised to CO2.

387 Oxidation and Reduction

3.1

To identify oxidation and reduction processes in the reaction between metal oxides and
carbon

Problem statement Materials

In the reaction between metal oxide and carbon, Powdered carbon, powdered copper(II) oxide, iron(III)
which reagent undergoes oxidation and which oxide and lead(II) oxide.
reagent undergoes reduction?

Experiment 3.1 3 Hypothesis Figure 3.1 Heating copper(II) oxide with carbon
(a) Carbon undergoes oxidation to form carbon
Procedure
dioxide gas.
(b) Copper(II) oxide, iron(III) oxide and lead(II) 1 A spatula of copper(II) oxide is placed in a crucible.
2 Another spatula of powdered carbon is added to
oxide undergo reduction to form copper, iron and
lead respectively. the copper(II) oxide.
3 The two substances are mixed thoroughly and the
Variables
(a) Manipulated variable : Type of metal oxide mixture is then heated strongly.
(b) Responding variable : Reaction products 4 The observations are recorded in the table given
(c) Constant variables : Carbon and the
below.
conditions of reaction 5 Steps 1 to 4 are repeated using iron(III) oxide and

Apparatus lead(II) oxide in place of copper(II) oxide.
Crucible, clay-pipe triangle, tripod stand, spatula and
Bunsen burner.

Results

Metal oxide Colour of metal oxide Observation
before heating

(a) Copper(II) oxide Black Brown spots (copper) are formed in the black mixture.

(b) Iron(III) oxide Brown Grey solid (iron) is formed.

(c) Lead(II) oxide Yellow Greyish-black solid (lead) is formed.

Discussion

In all the reactions above, metal oxides have lost oxygen to form the metals.
This shows that carbon has reduced metal oxides to the corresponding metals.

Conclusion

Carbon undergoes oxidation and the metal oxides undergo reduction. The hypothesis is accepted.
The chemical equations for the redox reactions are
(a) 2CuO(s) + C(s) → 2Cu(s) + CO2(g)
(b) 2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)
(c) 2PbO(s) + C(s) → 2Pb(s) + CO2(g)

Oxidation and Reduction 388

Oxidation Number SPM Table 3.1 Oxidation numbers of elements in the free
state
’08/P1

The oxidation number of an element is an Element Formula Oxidation number
arbitrary charge assigned to the element according
to a set of rules. Oxidation number is also known Hydrogen H2 0
as the oxidation state. Oxygen O2 0
Chlorine Cl2 0
Oxidation numbers of elements in ionic Sulphur S 0
compounds

1 An ionic compound can contain monatomic Iron Fe 0
ions (for example, Na+ and Cl– ions) or
polyatomic ions (for example, NH4+ or Copper Cu 0
SO42– ions).
2 For monatomic ions, the oxidation number
2 For a monatomic ion in an ionic compound, equals to the charge on the ion (Table 3.2).
the oxidation number is the charge on the ion.
Magnesium oxide, MgO is an ionic compound. Table 3.2 Oxidation numbers of monatomic ions
In magnesium oxide, magnesium exists as
magnesium ions, Mg2+ and oxygen exists as Simple ion Formula of ion Oxidation number
oxide ions, O2–. Thus, magnesium is said
to have the oxidation number of +2 and Hydrogen ion H+ +1
oxygen has the oxidation number of –2.
Sodium ion Na+ +1 3

Magnesium ion Mg2+ +2

Aluminium ion Al3+ +3

Oxidation numbers of elements in covalent Chloride ion Cl– –1
compounds
Oxide ion O2– –2
Carbon dioxide, CO2 is a covalent compound.
However, when determining the oxidation Nitride ion N3– –3
numbers of carbon and oxygen, you will have
to consider that this molecule exists as ions. 3 The sum of the oxidation states of all the atoms
• Each oxygen atom is considered as an oxide present in the formula of a compound is zero.
The compound can be an ionic compound or
ion (O2–) and carries a charge of –2. So two a covalent compound. For example,
oxide ions carry a total charge of –4. (a) in calcium carbonate, CaCO3
• As a result, each carbon ion carries a charge of
+4 so that CO2 exists as a neutral molecule. CaCO3

CO2 (+2) + (+4) + 3(–2) = 0

(+4) + 2  (–2) = 0 (b) in aluminium nitrate, Al(NO3)3
Al(NO3)3
Therefore, the oxidation number of carbon is
+4 and the oxidation number of oxygen is –2. (+3) + 3(+5) + 9(–2) = 0

Rules for Assigning Oxidation Numbers 4 For a polyatomic ion (that is, an ion that
contains a few atoms), the sum of the
To work out the oxidation number, the following oxidation numbers of all the atoms equals the
charge on the ion. For example,
rules must be applied. (a) in a sulphate ion, SO42–

1 An atom or a molecule of an element in the SO42– sum of the oxidation
(+6) + 4(–2) = –2 numbers is the same as the
SPM free state (that is, not combined with other charge on the polyatomic ion
’06/P1
’07/P1 elements) has an oxidation number of zero

(Table 3.1).

389 Oxidation and Reduction

(b) in an ammonium ion, NH4+ 8 The oxidation number of hydrogen in all its
compounds is +1 except in metal hydrides.
A metal hydride is a compound consisting
NH4+ sum of the oxidation
numbers is the same as the of hydrogen and a metal only. The oxidation
number of hydrogen in metal hydrides is –1.
(–3) + 4(+1) = +1 charge on the polyatomic ion
(a) Non-metallic hydride

(c) in a nitrate ion, NO3– HCl H2S

NO3– sum of the oxidation
numbers is the same as the
( +1) (–1) 2(+1) (–2)
(+5) + 3(–2) = –1 charge on the polyatomic ion (b) Metal hydrides


(d) in a dichromate(VI) ion, Cr2O72– NaH CaH2 AlH3

( +1) (–1)
Cr2O72– sum of the oxidation numbers (+2) 2(–1) (+3) 3(–1)
is the same as the charge on

2(+6) + 7(–2) = –2 the polyatomic ion 9 The oxidation number of oxygen in all its
compounds is –2 except in fluorine compounds

5 In a given compound, the more electro- (see point 6) and in peroxides. The oxidation
number of oxygen in peroxides is –1.
negative atom is given a negative oxidation
(a) Oxides
3 number and the less electronegative (or more

electropositive) atom has a positive oxidation

number. H2O BaO

I, Br, Cl, N, O, F 2 (+1) (–2) (+2) (–2)
(b) Peroxides
electronegativity increases

6 The oxidation number of fluorine remains H2O2 BaO2

unchanged in all its compounds and is 2(+1) 2(–1) (+2) 2(–1)

always –1. This is because fluorine is the most 10 Metals usually have positive oxidation numbers.
For example, the oxidation number of a Group
electronegative element. 1 element in a compound is always +1. The
oxidation number of a Group 2 element in a
compound is always +2.

F2O BrF3 Na3AlF6 11 Some metals show different oxidation numbers
in their compounds. For example, manganese
shows oxidation numbers of +2, +4, +6 and
2(–1) (+2) (+3) 3(–1) 3(+1) (+3) 6(–1) +7 (Table 3.3).



Notice that

(a) the oxidation number of oxygen in F2O is
+2 and not –2

(b) the oxidation number of bromine in BrF3 Table 3.3 Oxidation numbers of manganese
is +3 and not –1.

7 Chlorine, bromine and iodine usually have Compound MnSO4 MnO2 K2MnO4 KMnO4
+2 +4 +6 +7
the oxidation number of –1 except when Oxidation
number of
combined with a more electronegative element. manganese

For example,



HClO Cl2O



(+1) (+1) (–2) 2(+1) (–2) 12 Non-metals usually have negative oxidation
numbers. However, chlorine, bromine, iodine
KI KIO3 and nitrogen can have positive or negative
(+1) (–1) (+1) (+5) 3(–2) oxidation number (Table 3.4) depending on
the elements which combine with them.

Oxidation and Reduction 390

Table 3.4 Oxidation numbers of chlorine and nitrogen

Chlorine compound HCl HClO HClO2 ClO2 HClO3 HClO4
Oxidation number of chlorine –1 +1 +3 +4 +5 +7

Nitrogen compound NH3 N2O NO NO2– NO2 NO3–
+4 +5
Oxidation number of nitrogen –3 +1 +2 +3

Calculating the Oxidation Numbers of Elements in Compounds and Ions­

2 4 3

What is the oxidation number of manganese in the What is the oxidation number of sulphur in the
compound, KMnO4? thiosulphate ion, S2O32–?

Solution Solution
Let the oxidation number of manganese = x Let the oxidation number of sulphur = x
Oxidation number of K = +1 Oxidation number of O = –2
Oxidation number of O = –2
S2O32–
KMnO4
2(x) 3(–2)
+1 x 4(–2) Sum of the oxidation numbers of all atoms in the
Sum of the oxidation numbers of all the elements in polyatomic ion is equal to the charge on the ion.
the neutral compound, KMnO4, is zero. 2x + 3(–2) = –2
(+1) + x + 4(–2) = 0 x = +2
x = +7 The oxidation number of sulphur in S2O32– ion is +2.
The oxidation number of manganese in KMnO4 is +7.

3 1,1,1-trichloroethane (C2H3Cl3) is used as a solvent for
halogens. The oxidation numbers of carbon, hydrogen
Calculate the oxidation number of nitrogen in nitric and chlorine are shown below.
acid, HNO3.
C2H3Cl3
Solution
Let the oxidation number of nitrogen = x 2(0) + 3(+1) + 3(–1) = 0
Oxidation number of H = +1
Oxidation number of O = –2 The oxidation number of an element in the free state

HNO3 is always zero. However, in some cases (for example,

+1 x 3(–2) carbon in the Cc2oHm3Cplo3)u,ntdhecaonxaidlsaotiobne number of the
Sum of the oxidation numbers of all the elements in element in the zero.
the compound is zero.
(+1) + x + 3(–2) = 0 IUPAC Nomenclature of Inorganic Compounds
x = +5
The oxidation number of nitrogen in HNO3 is +5. 1 The IUPAC system is used to name inorganic
compounds in order to avoid confusion that
The oxidation number of nitrogen in HNO3 is +5 and may arise due to elements having different
not 5. The oxidation number of the element must be oxidation numbers.

accompanied by a positive or negative sign on the left 2 For example, there are two oxides of copper:
copper(I) oxide, Cu2O, and copper(II) oxide,
of the number. CuO. Copper(I) oxide is a brown powder
whereas copper(II) oxide is a black powder. The
Roman numerical figures (I) and (II) refer to the
oxidation numbers of copper in the compound.

391 Oxidation and Reduction

Oxidation Number and IUPAC Formula Oxidation Name of compound
Nomenclature of number of
Magnesium nitrate
1 (a) For an ionic compound or a covalent compound metal (NOT magnesium(II)
Mg(NO3)2 +2 nitrate)
compound that contains a metal with more
AlCl3 +3 Aluminium chloride
than one oxidation number, the Roman (NOT aluminium(III)
chloride)
numerical figure is stated in brackets

after the name of the metal to show the

oxidation number of the metal.

(b) For example, tin forms two types of chlorides,

SnCl2 (ionic) and SnCl4 (covalent). SnCl2 5 For a negative ion that contains a metal with
is called tin(II) chloride and SnCl4 is called more than one oxidation state, the Roman
tin(IV) chloride. number is stated in brackets after the name of
the metal, and the name of the metal ends with
(c) Similarly, lead(II) oxide refers to the -ate. For example,
(a) manganate(VII) refers to the negative ion
compound with the formula PbO whereas containing the manganese metal with
oxidation number +7, that is, MnO4–.
lead(IV) oxide refers to the compound (b) chromate(VI) refers to the negative ion
containing chromium metal with oxidation
2 PbO2. the formulae and the IUPAC number +6, that is, CrO42–.
Table 3.5 shows (c) dichromate(VI) refers to the negative ion
containing two chromium atoms with
names of some compounds containing metals. oxidation number +6, that is, Cr2O72–.
(d) hexacyanoferrate(III) refers to the negative
3 Table 3.5 Naming inorganic compounds ion containing six cyano (CN–) groups and
iron metal with oxidation number +3, that
containing metals is, [Fe(CN)6]3–.
Table 3.7 shows the names of some compounds
Formula Oxidation IUPAC name containing metals in negative ions.
of number of

compound metal

FeCl2 +2 Iron(II) chloride
FeCl3 +3 Iron(III) chloride
CuCl +1 Copper(I) chloride

CuSO4 +2 Copper(II) sulphate

Mn(NO3)2 +2 Manganese(II) nitrate

MnO2 +4 Manganese(IV) oxide Table 3.7 Name of compounds containing metals in
negative ions

3 The metallic elements in Groups 1, 2 and 3 of Formula Oxidation IUPAC name
the Periodic Table always have the oxidation of number of metal
numbers +1, +2 and +3 respectively. According to
the IUPAC nomenclature, the Roman numerical compound in negative ion
figure is not used in naming a compound if the
metal shows only one oxidation state in its K2MnO4 +6 Potassium
compounds. manganate(VI)

4 Table 3.6 shows some examples of naming KMnO4 +7 Potassium
compounds containing elements of Groups 1, manganate(VII)
2 and 3.
K2CrO4 +6 Potassium
Table 3.6 Naming inorganic compounds containing chromate(VI)
elements of Groups 1, 2 and 3
Potassium
Formula Oxidation K2Cr2O7 +6 dichromate(VI)
of number of Name of compound
K4Fe(CN)6 +2 Potassium
compound metal hexacyanoferrate(II)

K2SO4 +1 Potassium sulphate Potassium
(NOT potassium(I) hexacyanoferrate(III)
sulphate) K3Fe(CN)6 +3

Oxidation and Reduction 392

Notice that in K4Fe(CN)6, the negative ion is non-metal that shows more than one oxidation
[Fe(CN)6]4– while in K3Fe(CN)6, the negative number in its oxoanion, the Roman number
stated in brackets refers to the oxidation number
6 Oioxnoiasn[Fioe(nCsNa)r6e]3–a. nions (negative ions) that of the non-metal.
consist of an oxygen atom and another non- 7 Table 3.8 shows the common names and the
metallic atom. Examples of oxoanions are IUPAC names for some compounds containing
nitrate ion, NO3– and sulphate ion, SO42–. For a oxoanions.

Table 3.8 Common names and IUPAC names for some compounds

Molecular formula of Oxidation number IUPAC name Common name of
compound compound

Na2SO3 +4 (for S) Sodium sulphate(IV) Sodium sulphite
Na2SO4 +6 (for S) Sodium sulphate(VI) Sodium sulphate
NaNO2 +3 (for N) Sodium nitrate(III) Sodium nitrite
NaNO3 +5 (for N) Sodium nitrate(V) Sodium nitrate
NaClO +1 (for Cl) Sodium chlorate(I) Sodium hypochlorite

NaClO3 +5 (for Cl) Sodium chlorate(V) Sodium chlorate 3
HNO2 +3 (for N) Nitric(III) acid Nitrous acid
HNO3 +5 (for N) Nitric(V) acid Nitric acid
H2SO4 +6 (for S) Sulphuric(VI) acid Sulphuric acid

1 ’06 (a) the changes in oxidation numbers or

What is the oxidation number for oxygen in the (b) the transfer of electrons; that is, acceptance

thiosulphate ioBn , –S32 O32–? C +2 D +3 (gain) or donation (loss) of electrons.
A –2 3 Using oxidation numbers to identify redox

Solution reactions
The oxidation number for oxygen in a polyatomic (a) Oxidation is a process in which the oxidation
ion, such as NO3–, S2O32– or Cr2O72– is always –2.
Answer A number of the element is increased.
(b) Reduction is a process in which the oxidation
Comment
The oxidation number of oxygen in covalent number of the element is decreased.
compounds, such as CO2 or SO3 is also –2. 4 The following equation shows the reaction

between iron and chlorine.

(oxidation number increases)
oxidation

0 0 +3 –1
2Fe(s) + 3Cl2 → 2FeCl3
Oxidation and Reduction in Terms of
Changes in Oxidation Numbers reduction
(oxidation number decreases)
1 Most redox reactions occur without involving
hydrogen or oxygen. For example, the reaction In this redox reaction,
between chlorine and iron(II) chloride is a (a) the iron metal is oxidised to iron(III)
redox reaction:
chloride because its oxidation number
2FeCl2(aq) + Cl2(g) → 2FeCl3(aq) increases from 0 to +3.
2 For reactions that do not involve hydrogen or (b) chlorine (Cl2) is reduced to chloride
ion (Cl–) because its oxidation number
oxygen, an oxidation or reduction reaction is decreases from 0 to –1.
discussed in terms of

393 Oxidation and Reduction