The rate of reaction between magnesium carbonate and hydrochloric acid can be investigated by continuously monitoring the mass loss as carbon dioxide gas escapes:
MgCO3(s)+2HCl(aq)→MgCl2(aq)+H2O(l)+CO2(g) \text{MgCO}_3(\text{s}) + 2\text{HCl}(\text{aq}) \rightarrow \text{MgCl}_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g}) MgCO3(s)+2HCl(aq)→MgCl2(aq)+H2O(l)+CO2(g)In an experiment, a student adds an excess of large magnesium carbonate pieces to 50 cm3 of 0.5 mol dm-3 hydrochloric acid in a conical flask. The flask is placed on a digital balance, and a loose cotton wool plug is inserted into the neck of the flask. The mass loss is recorded over time.
Suggest why a loose cotton wool plug is placed in the neck of the flask, instead of:
Suggest why using a large excess of solid magnesium carbonate ensures that the rate of reaction is only affected by the changing concentration of the hydrochloric acid as the reaction proceeds.
Let mt m_t\,mt be the mass of CO2\text{CO}_2CO2 produced at time ttt, and let mtotalm_{\text{total}}mtotal be the total mass of CO2\text{CO}_2CO2 produced when the reaction is complete. Explain why the value (mtotal−mt)(m_{\text{total}} - m_t)(mtotal−mt) is directly proportional to the concentration of hydrochloric acid remaining in the flask at time ttt.
