This question was attempted by few candidates and the performance was good.
In (a), candidates correctly responded to the questions thus:
(iii) H H
| | ethane – 1,2-diol/ethylene glycol
H – C – C – H
In (b)(i), candidates correctly stated that carbohydrates are (naturally occurring) organic compounds containing carbon, hydrogen and oxygen with the hydrogen and oxygen present in the ratio of 2:1 (as in water).
In (b)(ii), they correctly gave example of each of monosaccharide, disaccharide and polysaccharide thus:
I. monosaccharide: glucose/fructose
II. disaccharide: sucrose/lactose/maltose
III. polysaccharide: starch/glycogen/cellulose
In (c)(i), candidates gave C = O /CHO as the functional group that makes the compound a reducing sugar.
In (c)(ii), candidates correctly stated what would be observed in I and II thus:
- brick red precipitate
- black/charred mass (of carbon is observed)
In (c)(iii), most candidates correctly wrote an equation for the reaction in 3(c)(ii) (II) as follows:
C6H12O6 → 6C + 6H2O
In (d), majority of the candidates correctly determined the molecular formula of Z thus:
mass of hydrogen in Z = 2 x 0.692 = 0.077g
mass of carbon in Z = 12 x 3.385 = 0.923g
Empirical formula of Z = CH.
(CH)n = 78
13n = 78
n = 78 = 6
Molecular formula of Z = C6H6