State the separate equations for the reactions of aluminium hydroxide and magnesium carbonate with hydrochloric acid.

Determine which of the two components of the tablet will neutralize the most acid.

On the leaflet which comes with the tablets it states that one of the side effects of the tablets is belching. Explain why this might occur.

${\text{Al(OH}}{{\text{)}}_3} + {\text{3HCl}} \to {\text{AlC}}{{\text{l}}_3} + {\text{3}}{{\text{H}}_2}{\text{O}}$;

${\text{MgC}}{{\text{O}}_3} + {\text{2HCl}} \to {\text{MgC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}} + {\text{C}}{{\text{O}}_2}$;

$n\,{\text{Al(OH}}{{\text{)}}_3} = \frac{{0.160}}{{77.95}} = 2.05 \times {10^{ - 3}}{\text{ (mol)}}$

and $n\,{\text{MgC}}{{\text{O}}_{\text{3}}} = \frac{{0.105}}{{84.32}} = 1.25 \times {10^{ - 3}}{\text{ (mol)}}$;

Do not penalize use of integer values for ${M_r}$.

${\text{Al(OH}}{{\text{)}}_3}$ neutralizes ${\text{6.15}} \times {\text{1}}{{\text{0}}^{ - 3}}{\text{ mol}}$ of acid and

${\text{MgC}}{{\text{O}}_{\text{3}}}$ neutralizes $2.50 \times {10^{ - 3}}{\text{ mol}}$ of acid;

due to carbon dioxide (from reaction of ${\text{MgC}}{{\text{O}}_{\text{3}}}{\text{/NaHC}}{{\text{O}}_{\text{3}}}$ with acid);

Most candidates were very familiar with at least one of the two equations. Some did not read the question carefully and stated the equation for magnesium hydroxide instead of magnesium carbonate.

Unfortunately many lost points in (b) as they did not carry through the calculations corresponding to the provided data and some did not realize that a calculation was required.

Part (d) was mostly correctly answered.