TJC Prelim P3

TEMASEK JUNIOR COLLEGE CHEMISTRY 9746/03 Higher 2 Paper 3 Free Response Thursday 24th SEPTEMBER 2009 2 hours Candidates answer on separate paper. Additional materials: Answer paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, centre/i ndex number & CG in the spaces provided on the cover page provided 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. You may use a calculator. A Data Booklet is provided. At the end of the examination, fasten all your work securely together 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. This question paper consists of 8 printed pages.

2 Answer any four questions 1 (a) The melting points of two halides are given below. Compound Formula Melting Point/ oC Aluminium fluoride AlF3 1291 Aluminium chloride AlCl3 178 Briefly relate these melting points to the structure of, and bonding in, each of these halides. [2] (b) Compound P, C 6H6O, was first used as a surgical antiseptic till it was later found to be carcinogenic. In the presence of anhydrous aluminium chloride, P can react with 3-chloropropene to yield Q, C9H10O. Both P and Q are found to decolourise aqueous bromine to form white precipitates R and S, respectively. Both R and S contain the same number of bromine atoms per molecule and S is found to be optically active. (i) Identify and draw the structural formulae of compounds P, Q, R and S explaining the reactions described. (ii) Write equations to illustrate the mechanism for the reaction of P with 3-chloropropene and anhydrous aluminium chloride. [9] (c) The trichlorides of nitrogen and phosphorus each react with water to give two products, but they react in different ways. Phosphorus trichloride, PC l 3, reacts to give HC l as the only chlorine- containing product. Nitrogen trichloride, NC l3, produces HOC l as the only chlorine-containing product. In each case, predict the other product and write a balanced equation for its production. Suggest an explanation for this difference in behaviour. [ 4 ] (d) Chrome Yellow is a natural yellow pigment made of lead(II) chromate. It is practically insoluble in water and is used in paints. The solubility product of PbCrO 4 at 15 0C is 1.69  10-14 mol2 dm-6. (i) Write an expression for the solubility product, K sp of PbCrO 4 and calculate the solubility of PbCrO 4, in mol -3 dm . (ii) Conce