AQA Jun 2011 Paper 2 Q8

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section b answer all questions in the spaces provided do not write outside the box a some scientists thought that the waste water from a waste disposal factory contained two sodium halides they tested a sample of the waste water they added three reagents one after the other to the same test tube containing the waste water the table below shows their results reagent added observations silver nitrate solution acidified with dilute nitric acid a cream precipitate formed dilute ammonia solution a yellow precipitate remained concentrated ammonia solution the yellow precipitate did not dissolve a i identify the yellow precipitate that did not dissolve in concentrated ammonia solution write the simplest ionic equation for the formation of this precipitate from silver ions and the correct halide ion identify the other sodium halide that must be present in this mixture of two sodium halides marks a ii give one reason why the silver nitrate solution was acidified before it was used in this test mark wmp jun chem do not write outside the box a iii the method that the scientists used could not detect one type of halide ion identify this halide ion give one reason for your answer marks b the scientists thought that the waste water also contained dissolved barium ions an aqueous solution of sodium sulfate can be used to test for the presence of dissolved barium ions write the simplest ionic equation for the reaction between barium ions and sulfate ions to form barium sulfate state what is observed in this reaction give a use for barium sulfate in medicine and explain why this use is possible given that solutions containing barium ions are poisonous marks question continues on the next page turn over wmp jun chem do not write outside the box the scientists also analysed the exhaust gases from an incinerator used to destroy waste poly ethene mass spectrometry showed that there was a trace gas with a precise mr in the exhaust gases from the incinerator the table below contains some precise relative atomic mass data atom precise relative atomic mass c h o use the data to show that the trace gas is ethene show your working suggest why both ethene and carbon monoxide might have been identified as the trace gas if the scientists had used relative atomic masses to a precision of only one decimal place write an equation for the incomplete combustion of ethene to form carbon monoxide and water only ethene is used to make poly ethene draw the displayed formula for the repeating unit of poly ethene name this type of polymer marks wmp jun chem c

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