OCR A Jan 2009 Paper 1 Q3

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3 A student used the internet to research chlorine and some of its compounds. (a) He discovered that sea water contains chloride ions. The student added aqueous silver nitrate to a sample of sea water. (i) What would the student see?[1] (ii) Write an ionic equation, including state symbols, for the reaction that would occur.[2] (iii) After carrying out the test in (i), the student added dilute aqueous ammonia to the mixture. What would the student see?[1] (b) The student also discovered that chlorine, Cl 2, is used in the large-scale treatment of water. (i) State one benefit of adding chlorine to water.[1] (ii) Not everyone agrees that chlorine should be added to drinking water. Suggest one possible hazard of adding chlorine to drinking water.[1] (c) The equation for the reaction of chlorine with water is shown below. Cl 2(g) + H2O(l) HCl(aq) + HCl O(aq) (i) State the oxidation number of chlorine in: Cl 2HClHCl O[1] (ii) The reaction of chlorine with water is a disproportionation reaction. Use the oxidation numbers in (i) to explain why.[2]OCR 2009<br />
 (iii) Chlorine reacts with sodium hydroxide to form bleach in another disproportionation reaction. Write an equation for this reaction.[1] (d) Two other chlorine compounds of chlorine are chlorine dioxide and chloric(V) acid. (i) Chlorine dioxide, Cl O2, is used as a bleaching agent in both the paper and the flour industry. When dry, Cl O2 decomposes explosively to form oxygen and chlorine. Construct an equation for the decomposition of Cl O2.[1] (ii) Chloric(V) acid has the following percentage composition by mass: H, 1.20%; Cl, 42.0%; O, 56.8%. Using this information, calculate the empirical formula of chloric(V) acid. Show all of your working. (iii) What does (V) represent in chloric(V) acid? empirical formula =[2][1] [Total: 14]OCR 2009 Turn over<br />

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