Chemistry · May / June 2017 · Paper 11 · Question 19

Magnesium carbonate reacts with dilute hydrochloric acid to form magnesium chloride, carbon dioxide and water. MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l) The rate of the reaction is found by reacting the magnesium carbonate and dilute hydrochloric acid in a conical flask. The mass of the flask and contents is measured every twenty seconds. [diagram: conical flask on a balance, labelled dilute hydrochloric acid, magnesium carbonate, balance] Which graph correctly shows the change in the mass of the flask and contents with time?

1. AGraph A: mass of flask and contents against time, curve rising from origin and levelling off
2. BGraph B: mass of flask and contents against time, curve rising from a non-zero value and levelling off
3. CGraph C: mass of flask and contents against time, curve decreasing from a maximum to zero
4. DGraph D: mass of flask and contents against time, curve decreasing from a maximum and levelling off at a non-zero value

As printed in the paper