This is the most popular question among the candidates and the performance was good.
In (a)(i), most candidates correctly stated that homologous series is a series/family of organic compounds with a general molecular formula, similarity in property and differing from successive member by CH2 or 14a.m.u.
In (a)(ii) .and (iii), candidates correctly gave two homologous series and corresponding examples present in petroleum from among the following:
- Alkanes - methane, ethane ete;
- Alkenes - ethene, propene ete;
- Cycloalkanes -cyclohexane,cyclopropane;
- Aromatics - benzene.
In (a)(iv), candidates were able to name two fractions obtained from the fractional distillation of petroleum from the following:
- Gas
- Petroleum ether;
- Gasoline(petrol)
- Gas oil (dieseloil)
- Lubricating oil;
- Bitumen and other residue.
In (a)(v), candidates correctly stated that there is a gradual change in the physical properties of petroleum fraction because of a steady change in molecular mass of the constituents.
In (b )(i) and (ii), majority of the candidates correctly wrote two-step balanced chemical equations for the reactions as follows:
(b) (i) |
I. |
C2H5OH(l) |
+ H2S04(1) |
|
|
C2HSHS04(I) |
+ |
H2O(1) |
|
|
|
heat |
|
|
|
|
|
|
|
II. |
C2HSHS04(l) |
|
C2H4(g) |
+ |
H2S04(1) |
|
|
|
|
|
A |
|
|
|
|
|
|
(ii) |
I. |
C2H5OHl(l) |
+ |
H2S04(1) |
|
C2HSHS04(1) |
+ |
H20(1) |
|
H. |
CfHsHS04(1) |
+ |
C2HsOH (1) |
|
C2HsOC2HS(g) + |
H2S04(1) |
In (c)(i), candidates correctly determined both the empirical and molecular formulae of the organic compound as follows:
(I) Empirical formula of the organic compound
C |
H |
0 |
52.0 |
13.3 |
34.7 |
12 |
1 |
16 |
| |
|
|
4.33 |
13.3 |
2.17 |
2.17 |
2.17 |
2.17 |
| |
|
|
2 |
6 |
1 |
Empirical formula |
= C2H6O |
|
(II) Molecular formula of the compound,
(C2HH5OH) n = 46
(12 x 2 + 6 x 1 +16) n = 46
46n = 46
n = 1
Molecular formula = C2H6O
In (c)(ii), most candidates drew two possible structures of the compound and correctiy name one of them. However, some of them lost marks by drawing the structures without showing the bonds ,(i.e. condensed
H H
I I
H-C- C-OH
I I
H H
Ethanol
H H
I I
H-C-O-C-H
I I
H H
Methoxymebnthane
