OCR A Jun 2013 Paper 1 Q2

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2 Hydrated aluminium sulfate, Al2(SO4)3x H2O, and chlorine, Cl2, are used in water treatment. (a) A student attempts to prepare hydrated aluminium sulfate by the following method. The student heats dilute sulfuric acid with an excess of solid aluminium oxide. The student filters off the excess aluminium oxide to obtain a colourless solution of Al2(SO4)3. (i) State the formulae of the two main ions present in the solution of Al2(SO4)3.and[2] (ii) Write an equation for the reaction of aluminium oxide, Al2O3, with sulfuric acid. Include state symbols.[2] (iii) What does x H2O represent in the formula Al2(SO4)3x H2O?[1] (iv) The student heats 12.606 g of Al2(SO4)3x H2O crystals to constant mass. The anhydrous aluminium sulfate formed has a mass of 6.846 g. Use the students results to calculate the value of x. The molar mass of Al2(SO4)3 = 342.3 g mol1. x =[3]OCR 2013<br />
 (b) A student tests chlorine gas with damp blue litmus paper. The litmus paper first turns a red colour and is then bleached. A reaction takes place between chlorine and water in the damp litmus paper. (i) Write the equation for the reaction between chlorine and water. Explain why the damp litmus paper turns a red colour as a result of this reaction.[2] (ii) Bleach is made by reacting chlorine with cold dilute aqueous sodium hydroxide. Suggest the formula of the ion responsible for bleaching.[1] [Total: 11]OCR 2013 Turn over<br />

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