This question was attempted by most candidates and the performance was fair.
In (a)(i), candidates correctly stated that X and Y represented dehydration and chlorination/addition reaction respectively.
In (a)(ii), candidates correctly stated the reagent used in each of the processes X and Y as follows:
X - (conc) H2SO4/alumina/CaO/H3PO4/ KH3SO4;
Y - Cl2 or chlorine
In (a)(iii), candidates wrote the equation for complete oxidation of CH3CH2OH thus:
CH3CH2OH + 2[O] CH3COOH + H2O
In (b)(i) most candidates correctly drew the structure of the molecule showing atoms and bonds thus:
In (b)(ii), only few candidates could correctly give the IUPAC name of the molecule as
2 – chloro – 3 – methylbutanoic acid.
In (b)(iii), candidates could not list the substituents in the molecule. The substituents are chloro (Cl) and methyl (CH3).
In (b)(iv), candidates knew that when NaHCO3/ Na2CO3 is added, there is effervescence or evolution of a colourless, odourless gas which turns lime water milky or on addition of ethanol and conc H2SO4 to the substance followed by warming, a sweet/fruity smell of alkanoate is formed or when magnesium ribbon is put in the substance, there is effervescence of a colourless, odourless gas which gives a pop sound with lighted taper.
In (c)(i), candidates correctly deduced that the hydrocarbon is either an alkene or a non – terminal alkyne.
Hence they deduced the formula as follows:
R. M. M. = 2 x vapour density
= 2 x 28
The general formula of alkene or non-terminal alkyne I
CnH2n or CnH2n-2
∴ 14n = 56 or 14n - 2 = 56
n = 4 or n is not a whole number
Hence, molecular formula = C4H8.
In (c)(ii) and (iii), only very few candidates could correctly draw and name the possible structures of the hydrocarbon thus: