VJC 2022 H2 Chem Prelim P3 qp

1 © VJC 2022 9729/03/PRELIM/22 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/03 Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 19 September 2022 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use a soft 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 18 2 / 22 3 / 20 Section B 4 OR 5 / 20 Total / 80 This document consists of 26 printed pages.

2 © VJC 2022 9729/03/PRELIM/22 Section A Answer all the questions in this section. 1 (a) (i) Under what conditions of temperature and pressure would you expect the behaviour of a real gas to be most like that of an ideal gas? [1] (ii) Barium ethanedioate, BaC 2O4, decomposes on heating to produ ce a mixture of two different gases, A and B, and an oxide only. Neither gas A nor gas B is an ideal gas. They have the following boiling points. gas boiling point / oC A –191.5 B –78.5 The graph below shows the variation of pV RT with pressure, p, for 1 mol each of gas A and gas B at constant temperature. Identify the graph that corresponds to gas A and explain your choice. [2] (iii) Free volume, V, refers to the volume of space between gas molecules. For an ideal gas, the free volume is essentially the same as the volume of the container. This can be calculated using the ideal gas equation, pV = nRT. The pressure of a 72 g gaseous sample containing gas A and gas B in a container of volume 400 cm3 is measured to be 3.36 ⨯ 107 Pa at 527 oC. Using the ideal gas equation, calculate the free volume of this gaseous sample in cm 3. Assume the gaseous sample has an average Mr = 36. [2] (iv) Explain why the volume you have calculated in (a)(iii) differs from that of the volume of the container. [1] (v) An impure sample of barium ethanedioate, BaC 2O4, of mass 0.500 g, is added to 50.0 cm 3 of 0.0200 mol dm –3 acidified MnO4–(aq) and heated. A redox reaction takes place and all BaC 2O4 are reacted. The resulting solution is titrated with Fe 2+(aq). The end-point is reached when 30.40 cm3 of 0.0500 mol dm–3 Fe2+(aq) has been added. C2O42– ⇌ 2CO2 + 2e– MnO4– + 8H+ + 5e– ⇌ Mn2+ + 4H2O Fe2+ ⇌ Fe3+ + e– Calculate the percentage by mass of BaC2O4 in the 0.500 g impure sample. Show your working. [Mr: BaC2O4, 225.3] [4]

3 © VJC 2022 9729/03/PRELIM/22 [Turn over …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

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5 © VJC 2022 9729/03/PRELIM/22 [Turn over (b) The elements of Group 14 can form monoxides and dioxides. The monoxides are un stable and will disproportionate into the ir element and dioxide. The equations for the disproportionation reactions are given in Table 1.1, together with some thermodynamic data for the reactions. Table 1.1 (i) Explain why the entropy change for the disproportionation of SiO(g) is much more negative than that for CO(g). [1] (ii) Explain why the entropy change for the disproportionation of PbO(s) is close to zero. [1] (iii) Use data from Table 1.1 to deduce the temperature above which the disproportionation of CO(g) becomes unfavourable. [1] (iv) Explain why CO(g) does not spontaneously disproportionate at room temperature. [2] (v) Carbon monoxide, CO, is a gas at room temperature and pressure. It contains a coordinate bond. Explain what is meant by a coordinate bond. [1] (vi) Dicarbon monoxide, C2O, is extremely reactive and is not encountered in everyday life. It is found in dust clouds in space and analysis has shown that the central atom is carbon with no unpaired electrons while the other carbon atom has a lone pair of electrons. Draw the structure of dicarbon monoxide, stating its shape and bond angle. [2] …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ………………………………………