2019 CJC Prelim H2 Chem P2 QP

9729/02/CJC JC2 Preliminary Examination 2019 [Turn over CANDIDATE NAME CLASS 2T CHEMISTRY 9729/02 Paper 2 Structured Questions Friday 23 August 2019 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 calculat or is expected, where appropriate. A Data Booklet is provided. At the end of examina tion, 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 Q 1 11 Q 2 18 Q 3 18 Q 4 10 Q 5 10 Q6 8 75 Paper 3 Q 1 22 Q 2 19 Q 3 19 Q 4 / 5 20 80 Paper 4 55 Total 240 Total % and Grade Catholic Junior College JC2 Preliminary Examination Higher 2

2 9729/02/CJC JC2 Preliminary Examination 2019 Answer all the questions in the spaces provided. 1 The Taj Mahal is an ivory-white marble monument in the Indian city of Agra. The famous building is becoming brown and green from environmental pollution. Acid rain accelerates the erosion of marble monuments. Marble consists primarily of calcium carbonate. (a) You should refer to the following solubility product data to help answer the following questions. Substance CaCO3 CaSO4 BaCO3 BaSO4 Solubility product / mol2 dm–6 1.69 x 10−8 2.03 x 10−3 8.28 x 10−9 8.84 x 10−11 The pollutant SO 2 dissolves in rainwater to form sulfuric acid. The sulfuric acid slowly converts calcium carbonate into solid calcium sulfate. (i) Write an equation for the reaction between calcium carbonate and sulfuric acid. ................................ ................................ ................................ .......................... [1] (ii) By calculating the solubilities of calcium carbonate and calcium sulfate, deduce why acid rain accelerates the erosion of marble. [3] The lifespan of Taj Mahal can be extended by treatment with an aqueous mixture of barium hydroxide, Ba(OH)2 and urea, CO(NH 2)2. As this soluti on soaks into the porous marble, the urea slowly hydrolyses forming ammonia and carbon dioxide. The carbon dioxide released reacts with the barium hydroxide in the mixture forming barium carbonate. (iii) Write an equation for the reaction between barium hydroxide and carbon dioxide. ................................ ................................ ................................ .......................... [1]

3 9729/02/CJC JC2 Preliminary Examination 2019 [Turn over (iv) By considering the reaction between surface barium carbonate and acid rain , explain how the erosion process can be slowed down. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .......................... [1] (b) Group 2 carbonates undergo decomposition in the same way at different temperatures. (i) Predict and explain the order of decomposition temperatures for the thr ee carbonates, MgCO3, CaCO3 and BaCO3. ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ........................... [3] The graph given below shows the change in mass when 2.00 g of each CaCO3 and BaCO3 were heated separately at a temperature, T oC. (ii) From the shapes of the graphs, identify CaCO3 and BaCO3 in the spaces provided below. Graph A: ................................ ................................ ................................ ............... Graph B: ................................ ................................ ................................ ............... [1] (iii) Sketch on the same axes , a graph that would be obtained by heating 2.00 g of magnesium carbonate, MgCO3, at the same temperature, T oC. [1] [Total: 11] 2.00 1.00 0 time mass/g Y(IO3)2 0 Graph A Graph B 1.12 g

4 9729/02/CJC JC2 Preliminary Examination 2019 2 Hydrogen peroxide is a common bleaching agent used to whiten wood pulp during the manufacture of paper. Transition metal ions such as Fe3+(aq), that are naturally present in wood pulp, would catalyse the decomposition of hydrogen peroxide, and hence reduce the bleaching efficiency. The wood pulp is therefore washed with a chelating agent such as EDTA to remove the transition metal ions before hydrogen peroxide is added. [EDTA = (–O2CCH2)2NCH2CH2N(CH2CO2–)2] (a) (i) Any Fe3+(aq) in the wood pulp would form a polydentate complex with EDTA. Give the formula of the complex formed. You may use the abbreviation ‘ EDTA’ in your answer. ................................ ................................ ................................ .......................... [1] (ii) State the coordination number of the complex in (a)(i). ................................ ................................ ................................ .......................... [1] (b) (i) H2O and NH 3 are simple molecules. Explain why, at room temperature, H 2O is a liquid while NH3 is a gas. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .......................... [2]

5 9729/02/CJC JC2 Preliminary Examination 2019 [Turn over (ii) While EDTA is a polydentate ligand, H2O and NH3 are examples of monodentate ligands in transition metal complexes. Explain what is meant by the term ligand. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .............................. ................................ ................................ ................................ .......................... [1] (c) Consider the ion [Cu(H2O)6]2+ present in an aqueous