AQA Jun 2013 Paper 4 Q5

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do not write outside the box lactic acid ch ch oh cooh is formed in the human body during metabolism and exercise this acid is also formed by the fermentation of carbohydrates such as sucrose c h o a i give the iupac name for lactic acid mark a ii write an equation for the formation of lactic acid from sucrose and water mark b a molecule of lactic acid contains an asymmetric carbon atom the lactic acid in the body occurs as a single enantiomer a racemic mixture racemate of lactic acid can be formed in the following two stage synthesis ch c o stage hcn ch c cn oh stage ch c cooh oh b i name and outline a mechanism for stage name of mechanism mechanism marks wmp jun chem do not write outside the box b ii give the meaning of the term racemic mixture racemate mark b iii explain how you could distinguish between a racemic mixture racemate of lactic acid and one of the enantiomers of lactic acid marks c a mixture of lactic acid and its salt sodium lactate is used as an acidity regulator in some foods an acidity regulator makes sure that there is little variation in the ph of food c i write an equation for the reaction of lactic acid with sodium hydroxide mark c ii the acid dissociation constant ka for lactic acid has the value mol dm at k calculate the ph of an equimolar solution of lactic acid and sodium lactate marks question continues on the next page turn over wmp jun chem do not write outside the box c iii suggest an alternative name for the term acidity regulator explain how a mixture of lactic acid and sodium lactate can act as a regulator when natural processes increase the acidity in some foods name explanation marks extra space d the cup shown is made from pla poly lactic acid pla is the condensation polymer formed from lactic acid the polymer is described as biodegradable and compostable compostable material breaks down slowly in contact with the moist air in a garden bin this produces compost that can be used to improve soil the manufacturers stress that pla cups differ from traditional plastic cups that are neither biodegradable nor compostable d i draw a section of pla that shows two repeating units marks wmp jun chem do not write outside the box d ii name the type of condensation polymer in pla mark d iii an intermediate in the production of pla is a cyclic compound c h o that is formed from two pla molecules draw the structure of this cyclic compound d iv traditional non biodegradable plastic cups can be made from poly phenylethene commonly known as polystyrene draw the repeating unit of poly phenylethene mark mark d v the manufacturers of pla claim that the material will break down to compost in just weeks suggest one reason why pla in landfill may take longer than weeks to break down mark turn over wmp jun chem

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