A student examines the reaction between calcium carbonate and hydrochloric acid. The reaction is represented by the equation: $\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$. The student carries out an investigation to find how the rate of this reaction changes when the concentration of hydrochloric acid is altered. Method: The student measures $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrochloric acid and pours it into a beaker, adds a known mass of calcium carbonate, starts a clock immediately, stops the clock when all of the calcium carbonate has reacted and records the reaction time. The experiment is repeated using different concentrations of hydrochloric acid. Water is added so that the total volume is the same in every experiment. All other variables are kept constant.
(a(i))[1]
State a test and the observation used to identify carbon dioxide gas.
(a(ii))[1]
State one further observation made when calcium carbonate is added to hydrochloric acid.
(b)[1]
Complete the table so that the two missing volumes are shown.
(c(i))[1]
State which experiment shows an anomalous reaction time.
(c(ii))[1]
Suggest a way the student can check whether the reaction time in (c)(i) is anomalous.
(c(iii))[1]
State which experiment gives the smallest rate of reaction.
(c(iv))[1]
Describe how the rate of this reaction changes when the concentration of the hydrochloric acid increases.
(d)[2]
Suggest two variables, apart from the concentration of hydrochloric acid or the mass of calcium carbonate, that influence the rate of this reaction.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Aqueous calcium hydroxide / limewater and white precipitate” …