AQA Jun 2012 Paper 2 Q9

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do not write outside the box a student investigated the chemistry of the halogens and the halide ions a in the first two tests the student made the following observations test observation add chlorine water to aqueous potassium iodide solution the colourless solution turned a brown colour add silver nitrate solution to aqueous potassium chloride solution the colourless solution produced a white precipitate a i identify the species responsible for the brown colour in test write the simplest ionic equation for the reaction that has taken place in test state the type of reaction that has taken place in test marks extra space a ii name the species responsible for the white precipitate in test write the simplest ionic equation for the reaction that has taken place in test state what would be observed when an excess of dilute ammonia solution is added to the white precipitate obtained in test marks extra space wmp jun chem b in two further tests the student made the following observations do not write outside the box test observation add concentrated sulfuric acid to solid potassium chloride the white solid produced misty white fumes which turned blue litmus paper to red add concentrated sulfuric acid to solid potassium iodide the white solid turned black a gas was released that smelled of rotten eggs a yellow solid was formed b i write the simplest ionic equation for the reaction that has taken place in test identify the species responsible for the misty white fumes produced in test marks extra space b ii the student had read in a textbook that the equation for one of the reactions in test is as follows h i h so i h s h o write the two half equations for this reaction state the role of the sulfuric acid and identify the yellow solid that is also observed in test marks extra space question continues on the next page turn over wmp jun chem do not write outside the box b iii the student knew that bromine can be used for killing microorganisms in swimming pool water the following equilibrium is established when bromine is added to cold water br i h o i hbro aq h aq br aq use le chatelier s principle to explain why this equilibrium moves to the right when sodium hydroxide solution is added to a solution containing dissolved bromine deduce why bromine can be used for killing microorganisms in swimming pool water even though bromine is toxic marks extra space end of questions wmp jun chem

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