2021 CJC H2 CHEM Prelim P2 QP

9729/02 CJC JC2 Preliminary Examination 2021 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/02 Paper 2 Structured Questions August 2021 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 19 printed pages and 1 blank page. For Examiner’s Use Paper 1 30 Paper 2 Q1 /14 Q2 /8 Q3 /12 Q4 /9 Q5 /15 Q6 /17 75 Paper 3 80 Paper 4 55 OVERALL (100%) Grade Catholic Junior College JC2 Preliminary Examination Higher 2

2 9729/02/CJC JC2 Preliminary Examination 2021 1 (a) Calcium is a Group 2 element. Table below shows the radius of the calcium atom and the radius of the calcium ion. Element Radius / pm Ca 197 Ca2+ 100 Explain the difference in size between calcium atom and calcium ion. ………...…....………….…………………………………… …………………………. ……………...…....………….……………………………………………………….[1] (b) Describe and explain the trend in ionic radii down Group 2. ………...…....………….…………………………………………………………….... ……………...…....………….………………………………………………………..... ………...…....………….…………………………………………………………….... ……………...…....………….……………………………………………………….[2] (c) A student investigates the thermal decomposition of the carbonates of Group 2 elements. He separately heats the carbonates of magnesium, calcium and barium and records the total volume of carbon dioxide collected every 10 seconds. In each experiment, he uses the same amount, in moles, of ea ch carbonate and uses the hottest flame of a Bunsen burner. The graph of his experimental results is given below. t/s

3 9729/02/CJC JC2 Preliminary Examination 2021 [Turn over (i) Write an equation to represent the thermal decom position of barium carbonate, indicating clearly the state symbols. ………………………………………………………………………………… [1] (ii) Identify the least thermally stable carbonate and explain how the graph supports your answer. ………...…....………….…………………………………………………………. ……………...…....………….……………………………………………………. ………...…....………….……………………………