RVHS Prelim P3_QP

RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION (II) CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2015 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of 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. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. 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 the end of the examination, fasten all your work securely together, with the cover page on top. This document consists of 12 printed pages.

2 River Valley High School 9647/03/PRELIM/15 2015 Preliminary Examination II 1 (a) (i) Sketch the trend of the ionic radii of the ions for the third period of the Periodic Table, from Na to Cl. In your sketch, explain the general trend of ionic radii across the period. [4] (ii) Chlorides of aluminium and phosphorus both react readily with water to form acidic solutions. Write equations to illustrate these reactions. [2] (b) Chloric(I) acid, HC lO, is a common disinfecting agent used in swimming pools for its strong oxidising ability. Chloric(I) acid is a weak acid and ionises according to the equation: HClO(aq) ⇌ H+(aq) + ClO(aq) Ka = 3.50  108 mol dm3 (i) To a swimming pool treated with HClO, Ca(OH)2(s) was added to maintain a relatively constant pH of 7.6. Write an equation to show to illustrate the reaction between calcium hydroxide and chloric(I) acid [1] (ii) Given that 56 g of Ca(OH) 2 is added, and the swimming pool has a capacity of 2500 m3, calculate the following:  [ClO] [HClO]  initial [HClO] of the freshly treated swimming pool. [2] (c) (i) The level of chloride content in tap water can be quantified by obtaining the mass of lead required to precipitate lead(II) chloride. At 298K, the solubility of lead( II) chloride is 2.45  102 mol dm3. Calculate the solubility product of lead(II) chloride. [1] (ii) Given that the acceptable limit of chloride ions in tap water is 250 ppm, calculate the minimum mass of lead required for precipitation to occur in a 50 cm3 sample of tap water. You may ignore the low concentration of lead( II) ions originally found in tap water. (1 ppm = 1 mg per litre) [2]

3 River Valley High School 9647/03/PRELIM/15 [Turn over 2015 Preliminary Examination II (d) A compound M has a molecular formula of C 8H10