The question was attempted by few candidates and performance as fair.
In part (a)(i), candidates could not correctly write an expression for the equilibrium constant Kp for the equilibrium reaction. The expected answer from candidates was
Kp = P2SO2
P2SO2 . P2O2
In (a)(ii) I – III, candidates correctly stated the effect of each of the factor on the yield of SO2.
However, some of them lost marks because they confused the yield with the equilibrium position. The expected answers from candidates were:
I. decrease in the yield of SO3 (g)
II. decrease in the yield of SO3 (g)
III. more of SO3 (g) will be formed / increase the yield of SO3 (g)
In (a) (iii), candidates correctly sketch the energy profile diagram as follows:
In part (b), candidates correctly mentioned two properties of carbon (IV) oxide that are responsible for its use as fire extinguisher, wrote a balanced equation for the reaction between carbon (IV) oxide and lime water and stated the function of carbon (IV) oxide in nuclear reactor.
In part (c), candidates knew that dilute H2SO4 would form an insoluble salt which covers the CaCO3 thus preventing further reaction and that conc. H2SO4 reacts with ammonia to form a salt.
In part (d), candidates correctly determined the number of moles of water molecules in the given hydrated salt.