TJC_H2_CHEM_P3_QN&ANS 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 the melt ing point s of aluminium fluoride, aluminium chloride and 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.  AlF3 has a giant ionic structure with strong ionic bonds present between Al3+ and F-. Large amount of energy is required to overcome the strong ionic bonds.  SiCl4 and aluminium chloride have simple molecular structure . Less energy is required to overcome the van der Waals’ forces present between the molecules.  AlCl3 dimerises to form Al2Cl6. Since A l2Cl6 has a larger and more polarisable electron cloud, stronger and more extensive van der Waals’ forces of attraction exist between the molecules. (ii) With the aid of equations, explain the reactions that take place when silicon tetrachloride and aluminium chloride are mixed with excess water.  SiCl4 undergoes hydrolysis with water using the energetically accessible vacant 3d orbitals in Si.  SiCl4(s) + 2H2O(l) → SiO2(s) + 4HCl (g) Or SiCl4(s) + 4H2O(l) → SiO2.2H2O(s) + 4HCl (g) (Note: do not accept Si(OH)4 as product)  AlCl3 undergoes hydration and hydrolysis . The high charge density of aluminium ion polarises water mole cules, weakening the O -H bond and causing it to break.  AlCl3(s) + aq → Al3+(aq) + 3Cl–(aq) [Al(H2O)6]3+ ⇌ Al(H2O)5(OH)2+ + H+ [7] (b) Silver chloride is sparingly soluble in water. AgCl(s) ⇌ Ag+(aq) + Cl–(aq) (i) Briefly describe any difference in t he solubility of silver chloride in water and in aqueous aluminiu