AQA Jun 2014 Paper 2 Q6 (with explained solutions) |

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AQA Jun 2014 Paper 2 Q6

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do not write outside the box this question is about group chemistry a sea water is a major source of iodine the iodine extracted from sea water is impure it is purified in a two stage process stage stage l h o so hl h so hl cl l hcl a i state the initial oxidation state and the final oxidation state of sulfur in stage marks oxidation state of s in so oxidation state of s in h so a ii state in terms of electrons what has happened to chlorine in stage mark b when concentrated sulfuric acid is added to potassium iodide iodine is formed in the following redox equations ki h so khso l s h o ki h so khso l h s h o b i balance the equation for the reaction that forms sulfur b ii deduce the half equation for the formation of iodine from iodide ions mark mark b iii deduce the half equation for the formation of hydrogen sulfide from concentrated sulfuric acid mark question continues on the next page turn over wmp jun chem do not write outside the box c a yellow precipitate is formed when silver nitrate solution acidified with dilute nitric acid is added to an aqueous solution containing iodide ions c i write the simplest ionic equation for the formation of the yellow precipitate mark c ii state what is observed when concentrated ammonia solution is added to this yellow precipitate mark c iii state why the silver nitrate solution is acidified when testing for iodide ions mark c iv explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in this test for iodide ions mark wmp jun chem do not write outside the box d chlorine is toxic to humans this toxicity does not prevent the large scale use of chlorine in water treatment d i give one reason why water is treated with chlorine mark d ii explain why the toxicity of chlorine does not prevent this use mark d iii write an equation for the reaction of chlorine with cold water mark e give the formulas of the two different chlorine containing compounds that are formed when chlorine reacts with cold dilute aqueous sodium hydroxide mark formula formula turn over for the next question turn over wmp jun chem

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mark scheme a level chemistry chem june marking guidance mark comments credit or electrons but not lone pair the idea of reduction alone is not enough ignore charge on the electron unless incorrect or multiples credit the electrons being subtracted on the lhs ignore state symbols ignore charge on the electron unless incorrect or multiples credit the electrons being subtracted on the rhs ignore state symbols of question a i m or iv m or vi a ii it chlorine has gained accepted electron s or correctly balanced half equation eg cl e cl b i ki h so khso i s h o b ii i i e or i i e b iii h so h e h s h o or so h e h s h o c i ag i agi only c ii the precipitate solid it does not dissolve is insoluble remains or a white cream yellow solid precipitate or stays the same or no visible observable change or no effect no reaction c iii the silver nitrate is acidified to react with remove an ions that would interfere with the test prevent the formation of other silver precipitates insoluble silver compounds that would interfere with the test remove other ions that react with the silver nitrate mark scheme a level chemistry chem june ignore state symbols not multiples ignore nothing happens ignore no observation credit a correct reference to ions that give a false positive do not penalise an incorrect formula for an ion that is written in addition to the name if only the formula of the ion is given it must be correct react with remove carbonate hydroxide sulfite ions ignore sulfate c iv hcl would form a white precipitate white solid with silver nitrate and this would interfere with the test it is not sufficient simply to state either that it will interfere or simply that the ions compounds react to form agcl of d i d ii d iii any one from to sterilise disinfect water to destroy kill microorganisms bacteria microbes pathogens the health benefit outweighs the risk or a clear statement that once it has done its job little of it remains or used in very dilute concentrations small amounts low doses cl h o hclo hcl or cl h o h clo cl or cl h o hcl o e in either order both required for one mark only naclo or naocl and nacl mark scheme a level chemistry chem june ignore to clean water ignore water purification and germs credit remove bacteria etc prevent algae credit hocl or cloh or multiples credit other ionic or mixed representations ignore state symbols credit correct ionic formulae give credit for answers in equations unless contradicted of

Question 1 2 3 4 5 6 7 8 9

Topics to revise

AQA > Organic Chemistry > Optical isomerism >

1 Optical isomerism

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Inorganic chemistry > Group 7 AS >

3 Reaction of halide with silver nitrate

AQA > Organic Chemistry > Amines >

3 Reactions involving amines

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

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