PJC_H1_CHEM_P2_ANS

PIONEER JUNIOR COLLEGE 2015 JC2 PRELIMINARY EXAMINATION HIGHER 1 CHEMISTRY 8872/02 Paper 2 15 September 2015 Candidates answer Section A on the Question Paper Additional Materials: Data Booklet Writing Paper 2 hours READ THESE INSTRUCTIONS FIRST Write your name, index no and CT group on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Section A Answer all questions. Section B Answer any two questions on separate writing paper. Begin each question in a fresh sheet of writing paper. 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 16 printed pages Name: Index No.: CT Group: 14 FOR EXAMINER’S USE Section A Section B 1 / 10 5 / 20 2 / 9 6 / 20 3 / 9 7 / 20 4 / 12 Penalty s.f. / units TOTAL / 80

2 Section A (40 marks) Answer all questions in the spaces provided. 1 The diagram below shows the reactions of an aqueous salt, A. orange solution B brown solution C colourless solution colourless solution cream precipitate yellow precipitate colourless A(aq) AgNO3(aq)AgNO3(aq) A has the following composition by mass: K, 41.1%; S, 33.7%; O, 25.2%. The relative formula mass, Mr, of A is 190.4. One formula unit of A contains only one type of anion. (a) Determine the formula of the salt A. Let the mass of salt A be 100g. K S O Mass / g 41.1 33.7 25.2 Amount / mol 1.0512 1.0498 1.575 Ratio 1.0013 1.000 1.500 Simplest Ratio 2 2 3 Empirical formula of salt is K2S2O3. Let formula of salt be (K2S2O3)n. [2(39.1) + 2(32.1) + 3(16.0)]n = 190.4 n = 1 [2] Formula of salt is K2S2O3.

3 (b) Suggest the identities of the cream precipitate and the yellow precipitate. Cream precipitate: AgBr Yellow precipitate: AgI [1] (c) Suggest the identities of B and C. B: Br2 C: I2 [1] (d) With reference to the Data Booklet, show, by means of two ionic equations, how the yellow precipitate is formed from C. 2S2O3 2-(aq) + I2(aq)  2I-(aq) + S4O6 2-(aq) I-(aq) + Ag+(aq)  AgI(s) [2] (e) For the reaction of A and B, a titration was carried out to determine if the sulfur - containing pr