16 (B410U20-1) Examiner only 11. Adam investigated how the initial rate of reaction between hydrochloric acid and magnesium carbonate at 20 °C is affected by the concentration of the acid. The equation for the reaction is as follows. MgCO3(s) + 2HCl(aq) MgCl2(aq) + CO2(g) + H2O(l) He used 0.50 g of magnesium carbonate and 40 cm3 of 0.20 mol dm–3 hydrochloric acid. He measured the volume of carbon dioxide produced at regular time intervals as the reaction proceeded. Part of the apparatus used for the experiment is shown below. The magnesium carbonate was placed in the small glass container which was tipped over to start the reaction and a stopwatch was started at the same time. © WJEC CBAC Ltd. hydrochloric acid magnesium carbonate (a) Name the apparatus used to collect and measure the volume of the gas produced. [1] (b) Suggest an experimental method other than measuring the volume of gas that would allow the rate of this reaction to be studied. [2] (c) Elinor told Adam that in this experiment the carbonate needed to be in excess. He replied that it was. Is he correct? Justify your answer. [2] gas collected directly (B410U20-1) 17 Examiner only (d) Adam plotted his results as follows. © WJEC CBAC Ltd. 0 0 10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 6 7 8 9 10 Time (minutes) Volume of carbon dioxide (cm3) By drawing a tangent to the curve calculate the initial rate of this reaction. State the unit. [2] Rate = ................................................. Unit ................................................. Turn over. 18 (B410U20-1) Examiner only (e) He then repeated the experiment using 40 cm3 of 0.10 mol dm–3 hydrochloric acid. Sketch on the graph in (d) the curve he would expect to obtain. Explain any differences in the curves. [3] (f) State one condition, other than temperature and pressure, which would need to be kept constant in this investigation. [1] END OF PAPER © WJEC CBAC Ltd. 11 Examiner only (B410U20-1) 19 © WJEC CBAC Ltd. For continuation only.