Calcium carbonate reacts with hydrochloric acid. The reaction gives off carbon dioxide gas. Line X on the graph shows the volume of carbon dioxide formed against time when 100 cm3 of 1.0 mol dm–3 of hydrochloric acid reacts with calcium carbonate chips at C.20° There was an excess of calcium carbonate chips.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O(l)
Which line best represents the volume of carbon dioxide formed against time when the reaction is repeated with 50 cm3 of 2.0 mol dm–3 of hydrochloric acid reacting with excess calcium carbonate chips at C?

Answer:

22) B

A higher concentration of acid indicates that the rate of reaction would be faster than the original experiment.

Only B and A fit this condition so we can eliminate C, D and E.

Since the amount of acid present is the same (100cm³ x 1 mol/dm³ = 50cm³ x 2mol/dm³), the overall amount of carbon dioxide produced would be the same as the initial experiment. Therefore, B is the answer.