PJC_H2_CHEM_P3_(Answers)

PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION HIGHER 2 CANDIDATE NAME CT INDEX GROUP NUMBER CHEMISTRY 9647/03 Paper 3 Free Response 24 September 2014 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Graph Paper Data Booklet Cover Page READ THESE INSTRUCTIONS FIRST Write your name, CT group and index number on all work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough workings. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At then end of the examination, fasten all your work securely together. This document consists of 20 printed pages. 1 3

© PJC 2014 9647/03/JC2 Prelim/2014 2 Answer any four questions. 1 (a) The graph below shows the second and th ird ionisation energies for the first d-block elements scandium to zinc. Ionisation energy / kJ mol -1 By writing relevant electronic configuration, explain why (i) the second ionisation energy of ch romium is higher than that of manganese. Cr + :1s2 2s2 2p6 3s2 3p6 3d5 Mn+ :1s2 2s2 2p6 3s2 3p6 3d5 4s1 The second electron removed from chro mium is from an inner 3d subshell which is closer to the nucleus and required a higher energy to remove it. (ii) the third ionisation energy of iron is lower than that of manganese. Fe 2+ : 1s2 2s2 2p6 3s2 3p6 3d6 Mn2+ : 1s2 2s2 2p6 3s2 3p6 3d5 The third electron from Fe experiences inter-electronic repulsion as it is removed from one 3d orbital containing a pair of electrons and required a lower energy to remove it. [4] (b) An aqueous solution contains a mixture of iron(III) and zinc ions. (i) Draw a diagram to show the bonding in the hexaaquairon(III) complex ion. 2nd IE 3rd IE

© PJC 2014 9647/03/JC2 Prelim/2014 3 . Fe H2O H2O H2O H2O OH2 OH2 3+ (ii) Describe, in a sequence of steps, how you would separate the two cations so that they are obtained as Fe 3+(aq) and Zn2+(aq). Write equations for all the reactions that iron(III) ion and its compound have undergone. You are only provided with HNO3(aq) and NaOH(aq). 1. To 2 cm 3 of solution in a test tube, add NaOH(aq) until in excess 2. Filter the mixture 3. Add excess HNO3(aq) to the residue to obtain Fe3+(aq) 4. Add excess HNO3(aq) to the filtrate to obtain Zn2+(aq) Precipitation reaction: Fe3+(aq) + 3OH(aq) → Fe(OH)3(s) Acid Base reaction: Fe(OH)3(s) + 3HNO3(aq) → Fe(NO3)3(aq) + 3H2O(l) [5]