Following the experiment, the students proposed the following hypothesis:

“Since sulfuric acid is a strong acid, two other strong acids such as nitric acid, HNO₃(aq) or hydrochloric acid, HCl(aq), could also be used in this experiment”.

Suggest one problem with this hypothesis.

The students also explored the role of sulfuric acid in everyday processes and found that sulfuric acid present in acid rain can damage buildings made of limestone. Predict the balanced chemical equation for the reaction between limestone and sulfuric acid, including state symbols.

\({\text{NO}}_{\text{3}}^ - \) and \({\text{C}}{{\text{l}}^ - }\) anions may also react with \({\text{KMn}}{{\text{O}}_{\text{4}}}\) / \({\text{HN}}{{\text{O}}_{\text{3}}}\) is an oxidizing agent / (HCl will not work as) \({\text{C}}{{\text{l}}^ - }\) reacts with \({\text{MnO}}_{\text{4}}^ - \) (to form \({\text{C}}{{\text{l}}_{\text{2}}}\)) / HCl oxidized / OWTTE;

For HCl, allow correctly balanced chemical equation:

2MnO₄^–+10Cl^–+16H⁺\( \to \)2Mn²⁺+5Cl₂+8H₂O

Accept NO₃^– and Cl^– may react with KMnO₄/Fe²⁺.

\({\text{CaC}}{{\text{O}}_3}{\text{(s)}} + {{\text{H}}_2}{\text{S}}{{\text{O}}_4}{\text{(aq)}} \to {\text{CaS}}{{\text{O}}_4}{\text{(s)}} + {{\text{H}}_2}{\text{O(l)}} + {\text{C}}{{\text{O}}_2}{\text{(g)}}\)

correct chemical equation;

correct state symbols;

Allow CaSO₄(aq) instead of CaSO₄(s).

M2 can only be scored if M1 is correct.

Award [1max] if H₂CO₃(aq) is given instead of H₂O(l) + CO₂(g).

Most candidates were able to state the function of iron in the body but unable to explain why a reading of the top meniscus is taken for the KMnO₄ titration, which suggests limited practical experience. Some candidates calculated the moles of Fe using the mass of tablets rather than using mole ratio and titre results. most candidates were able to define ‘reduction’ and determine the oxidation number, although some were penalized for incorrect notation. Many did not know how to prevent the formation of MnO₂ precipitate or why HCl or HNO₃ are not used in this titration.

Most candidates were able to state the function of iron in the body but unable to explain why a reading of the top meniscus is taken for the KMnO₄ titration, which suggests limited practical experience. Some candidates calculated the moles of Fe using the mass of tablets rather than using mole ratio and titre results. most candidates were able to define ‘reduction’ and determine the oxidation number, although some were penalized for incorrect notation. Many did not know how to prevent the formation of MnO₂ precipitate or why HCl or HNO₃ are not used in this titration.