A student adds calcium carbonate to an excess of dilute hydrochloric acid in a conical flask on a balance. The flask is left open, so gas can leave it.
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)\mathrm{CaCO_3(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{CaCl_2(aq)} + \mathrm{H_2O(l)} + \mathrm{CO_2(g)}CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
The student records these balance readings.
| Reading | Mass / g |
|---|---|
| flask and hydrochloric acid | 148.50 |
| flask, acid and calcium carbonate at the start | 151.00 |
| after 3 minutes | 150.02 |
| after 6 minutes | 149.91 |
| after 9 minutes | 149.91 |
Relative formula masses: CaCO3=100\mathrm{CaCO_3} = 100CaCO3=100, CO2=44\mathrm{CO_2} = 44CO2=44.
Calculate the mass of carbon dioxide that would be given off if all of the calcium carbonate reacted.
Use the results and your answer to part (a) to explain whether all of the calcium carbonate had reacted after 3 minutes and whether the final results support the calculated mass of carbon dioxide.
The student repeats the experiment in a sealed flask, so no gas can leave. Explain how the balance reading at the end of this repeat would compare with the reading at the start.
142 exam-style questions on Edexcel GCSE Chemistry 2.6 Calculations involving masses, covering 2.6.1 Relative formula mass and percentage composition, 2.6.2 Empirical and molecular formulae, 2.6.3 Conservation of mass, 2.6.4 Reacting masses and concentration in g dm⁻³, 2.6.5 The mole and the Avogadro constant, and 2.6.6 Limiting reactants and stoichiometry. Each one has a worked solution and a mark scheme showing where the marks go.