2023 SAJC H2 Chem Prelim P2 (Ans)

ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 2 S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 30 August 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work that you hand in. Write in dark blue or black pen. You may use a 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 __ printed pages (including this cover page). For Examiner’s Use Q1 9 Q2 21 Q3 17 Q4 9 Q5 19 Total 75

2 1 (a) Table 1.1 lists the number of protons, neutrons and electrons in five different particles. Each particle may be an atom, an anion or a cation. Table 1.1 particle number of protons number of neutrons number of electrons A 17 18 17 B 17 20 17 C 17 20 18 D 18 22 18 E 18 22 17 F 19 20 19 G 19 20 18 (i) Use the information in Table 1.1 to identify • the two particles which are a pair of isotopes of the same element __________________________________________________________ A and B • the uncharged particle with no unpaired electrons __________________________________________________________ D [2] (ii) Deduce which particle is smaller, F or G. Explain your answer. [2] F have the same number of protons as G and hence, same nuclear charge. F has one more electron shell than G, so there is stronger attraction between the nucleus and the remaining electrons / electrons would be closer to the nucleus in G and G would be smaller. (b) Phosphorus pentachloride, PCl5, is a useful reagent in organic synthesis. It exists in equilibrium with PCl3 and chlorine gas as shown below: PCl5 (g) PCl3 (g) + Cl2 (g) ΔH = +124 kJ mol‒1 At equilibrium, at 200 °C and a total pressure of 5 atm, 40% of PC l5 is dissociated. (i) Write an expression for Kp for the above equilibrium. [1] Kp = PPCl3PCl2 PPCl5

3 (ii) Calculate a value for Kp at 200 °C and state its units. [2] PCl5 PCl3 + Cl2 Initial / mol Z 0 0 Change / mol -0.4 z +0.4 z +0.4 z Eqm / mol 0.6 z 0.4 z 0.4 z Total moles = 1.4 z PPCl5 = (0.6 z / 1.4 z) x 5 = 2.143 atm PPCl3 = PCl2 = (0.4 z / 1.4 z) x 5 = 1.429 atm Kp = 0.953 atm (iii) Predict and explain the effect of increasing the temperature on the value of Kp. [2] When temperature increases, the system will favour the (endothermic) forward reaction to absorb the excess heat / d