TJC_H2_CHEM_P3_QN Prelim

1 9647/03/TJC Prelim 2014 [Turn Over CHEMISTRY (H2) 9647/03 Paper 3 Free Response Tuesday 16th September 2014 2 hours Candidates answer on separate paper. Additional materials: Answer paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name , Civics Group and Index number in the spaces provided on the cover page and on all the 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 working. 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 g iven in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This question paper consists of 15 printed pages.

2 9647/03/TJC Prelim 2014 [Turn Over Answer any four questions. 1 (a) The table below shows t he melting point s of aluminium fluoride, aluminium chloride an d silicon tetrachloride. Compound Melting point/ °C Aluminium fluoride 1290 Aluminium chloride 190 Silicon tetrachloride -90 (i) Explain the difference in their melting points in terms of their structure and bonding. (ii) With the aid of equations, explain the reactions that take place when silicon tetrachloride and aluminium chloride are mixed with excess water. [7] (b) Silver chloride is sparingly soluble in water. AgCl(s) ⇌ Ag+(aq) + Cl– (aq) (i) Briefly describe any difference in the solubility of silver chloride in water and in aqueous aluminium chloride. (ii) Given that the solubility product of silver chloride is 1 x 10 -10 mol2 dm-6, calculate the maximum [Ag+(aq)] before a precipitate starts to form in 0.0500 mol dm -3 of aqueous aluminium chloride. Silver ions form complexes with ammonia and with amines. Ag+(aq) + 2RNH2(aq) ⇌ [Ag(RNH2)2]+(aq) (iii) Write a KC expression for this reaction and state its units. (iv) KC has a numerical value of 1.7 x 10 7 when R = H. Using your expression for K C, calculate the [NH3(aq)] needed to change the [Ag+(aq)] in a 0.010 mol dm–3 solution of silver nitrate to the value that you calculated in (b)(ii). (v) Explain whether you would expect the K C for the reaction where R = C 2H5 to be greater or less than that for the reaction where R = H. [8]

3 9647/03/TJC Prelim 2014