CJC H2 Chem 2012 Prelim P2 Soln

3 9647/02/CJC JC2 Preliminary Exam 2012 (c) The temperature of the Bunsen flame varies depending on the ratio of the fuel to oxygen burnt. Besides keeping to the same fuel to oxygen ratio, s uggest how you would control another factor in the heating to ensure a fair comparison of the rate of decomposition of different carbonates. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [1] (d) Other than the use of safety goggles, state one hazard that must be considered when planning the experiment and suggest how you would keep this risk to a minimum. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [2] (e) With reference to the apparatus in (b), show how you would calculate the mass of each carbonate used in the experiment. [Mr: MgCO3 = 84.3; CaCO3 = 100.1; SrCO3 = 147.6; BaCO3 = 197.0] [2] · Bunsen burner at same distance from the reaction vessel. 1. “hot” apparatus – use heat-proof gloves or let apparatus cool before handling 2. potential suck back (if water allowed to suck back, hot boiling tube would crack and shatter) – remove delivery tube from water when heating is stopped. Note: 1. Vol of CO2(g) collected must not exceed capacity of collection device. 2. Mass of each carbonate used must contain the same number of moles. Let volume of CO2(g) collected = 40 cm3 Since molar gas volume at r.t.p. = 24 dm3, mol of CO2 = = 1.67 × 10–3 mol MCO3 ® MO + CO2 \ minimum mol of MCO3 = mol of CO2 = 1.67 × 10–3 mol Mr of MCO3 = (Ar of M ) + [12.0 + 3(16.0)] = (Ar of M ) + 60.0 Let mol of carbonate = 2.00 × 10–3 mol mass of MCO3 = nMr = 2.00 × 10–3 × [(Ar of M ) + 60.0] \ mass of MgCO3 = (2.00 × 10–3) × 84.3 = 0.169 g mass of CaCO3 = (2.00 × 10–3) × 100.1 = 0.200 g mass of SrCO3 = (2.00 × 10–3) × 147.6 = 0.295 g mass of BaCO3 = (2.00 × 10–3) × 197.0 = 0.394 g [vol and mol of CO2(g)] [same mol of each carbonate]

4 9647/02/CJC JC2 Preliminary Exam 2012 (f) Draw a table with appropriate headings (and units) to show the data you would record and the values you would calculate in order to plot a suitable graph to show the variation in the rates of decomposition of the carbonates. Sketch, and explain, the shape of the graph you would expect from your results. Label clearly the axes. Explanation: ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. [4] [Total: 12] 0 Mr of MCO3 / s–1 Mr time / s time