2019 ASRJC Prelim H2 Chem P3 QP

ASRJC JC2 PRELIMS 2019 9729/03/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2019 JC 2 PRELIMINARY EXAMINATIONS CHEMISTRY 9729/03 Higher 2 18 September 2019 Paper 3 Free Response 2 hours Candidates answer on separate Answer Booklet. Additional Materials: Answer Booklet 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 a pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. 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. 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 15 printed pages and 1 blank page.

2 ASRJC JC2 PRELIMS 2019 9729/03/H2 Section A Answer all the questions from this section. 1 (a) Iron(III) cation complexes with a thiocyanate anion (SCN –) to form the iron( III) thiocyanate complex, [Fe(SCN)]2+ at 298 K, according to the following equation. Fe3+(aq) + SCN–(aq) ⇌ [Fe(SCN)]2+(aq) H < 0 yellow colourless blood red (i) Write an expression for Kc for this reaction, stating its units. [2] (ii) The Kc value of this reaction is 4.99 x 102. Calculate the percentage of [Fe(SCN)]2+ in a Fe3+–[Fe(SCN)]2+ mixture when [SCN–] = 5.00 x 10–3 mol dm–3. [2] (iii) State and explain the difference in observations when the reaction is carried out at 500 K. [2] (b) Describe the variations in melting points of the elements sodium to chlorine and explain these variations in terms of their structures and bonding. [5] (c) Compounds B, C, D and E are oxides or chlorides of Period 3 elements. B and C have high melting points while D and E have low melting points. B is insoluble in water but soluble in hot concentrated sodium hydroxide. When water was added separately to 0.100 mol each of C, D and E, a neutral solution was obtained for C while an acidic solution was obtained for D and E. The resulting solution of D required 0.500 mol of silver nitrate for complete precipitation. 1 mol of E requ