TJC Prelim P2_Ans

1 2017 TJC H2 Chemistry Preliminary Exam [Turn over s CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 11 September 2017 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group, centre number, index number and name 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 the 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 18 printed pages For Examiner’s Use 1 / 22 2 / 15 3 / 21 4 / 8 5 / 9 Paper 1 / 30 Paper 3 / 80 Total PRELIMINARY EXAMINATIONS HIGHER 2

2 2017 TJC H2 Chemistry Preliminary Exam [Turn over Answer all the questions 1 Silver chloride is an important photosensitive inorganic material widely used in photographic applications. It is industrially produced by mixing solutions of silver nitrate and sodium chloride. Ag+(aq) + Cl-(aq) AgCl(s) ∆Hppto = -65.7 kJ mol-1, ∆Sppto = -34.3 J mol-1 K-1 (a) (i) Suggest whether a lower or higher temperature should be used to increase the yield of silver chloride. Explain your answer. [2] • A lower temperature should be used. • By Le Chatelier’s Principle , the system will favour the forward exothermic reaction to counteract the lowered temperature. Hence, the position of equilibrium shifts to the right increasing the yield of silver chloride. (ii) Calculate ∆Go of the precipitation of AgCl. [1] • ΔGᶿ = ΔHᶿ - TΔSᶿ = -65.7 – (298)(-34.3/1000) = -55.5 kJ mol-1 (iii) In view of your answer in (a)(ii), comment on the solubility of silver chloride in water. [1] • Since ΔGᶿ is negative, precipitation is spontaneous. Hence, Ag Cl is insoluble/sparingly soluble in water. (b) (i) Lattice energies are not measured directly. The value calculated using Hess’ Law and the Born-Haber cycle is the experimental lattice energy. Using ∆H ppto of AgCl(s), the following data and relevant data from the Da