AQA Jun 2014 Paper 4 Q2

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do not write outside the box this question is about alkalis and carboxylic acids in this question all data are quoted at c a carboxylic acids are weak acids state the meaning of the term weak as applied to carboxylic acids mark b write an equation for the reaction of propanoic acid with sodium carbonate mark c calculate the ph of a mol dm solution of calcium hydroxide the ionic product of water kw mol dm give your answer to decimal places marks extra space wmp jun chem do not write outside the box d the value of the acid dissociation constant ka for benzenecarboxylic acid c h cooh is mol dm d i write an expression for the acid dissociation constant ka for benzenecarboxylic acid mark d ii calculate the ph of a mol dm solution of benzenecarboxylic acid give your answer to decimal places marks extra space question continues on the next page turn over wmp jun chem do not write outside the box d iii a buffer solution with a ph of is made using benzenecarboxylic acid and sodium benzenecarboxylate calculate the mass of sodium benzenecarboxylate mr that should be dissolved in dm of a mol dm solution of benzenecarboxylic acid to produce a buffer solution with a ph of the value of the acid dissociation constant ka for benzenecarboxylic acid c h cooh is mol dm marks extra space wmp jun chem do not write outside the box e two solutions one with a ph of and the other with a ph of were left open to the air the ph of the ph solution changed more than that of the other solution suggest what substance might be present in the air to cause the ph to change explain how and why the ph of the ph solution changes marks substance present in air explanation turn over for the next question turn over wmp jun chem

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