AQA Jun 2011 Paper 4 Q2 (with explained solutions) |

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AQA Jun 2011 Paper 4 Q2

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do not write outside the box this question is about the ph of some solutions containing potassium hydroxide and ethanoic acid give all values of ph to decimal places a i write an expression for ph mark a ii write an expression for the ionic product of water kw mark a iii at c a mol dm solution of potassium hydroxide has a ph of calculate the value of kw at c marks extra space wmp jun chem do not write outside the box b at c the acid dissociation constant ka for ethanoic acid has the value mol dm b i write an expression for ka for ethanoic acid mark b ii calculate the ph of a mol dm solution of ethanoic acid at c marks extra space question continues on the next page turn over wmp jun chem do not write outside the box c at c the acid dissociation constant ka for ethanoic acid has the value mol dm c i calculate the ph of the solution formed when cm of mol dm potassium hydroxide are added to cm of mol dm ethanoic acid at c marks extra space wmp jun chem do not write outside the box c ii calculate the ph of the solution formed when cm of mol dm potassium hydroxide are added to cm of mol dm ethanoic acid at c at c kw has the value mol dm marks extra space turn over for the next question turn over wmp jun chem

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chem unit kinetics equilibria and organic chemistry june marking guidance mark comments penalise missing here and not elsewhere allow brackets but must have charges if wrong no further mark log h h oh question a i a ii b i b ii a iii mark independently from a ii h kw ka must have charges and all brackets allow acid salt shown must be ch cooh not ha and correct formulae needed in ph values penalise fewer than sig figs each time but allow more than dp for values above allow sfs do not insist on dp ka h h ph or allow ha if shown but not done gets ph scores allow mark for ph conseq to their h here only chem unit kinetics equilibria and organic chemistry june c i in ph values penalise fewer than sig figs each time but allow more than dp for values above allow sfs do not insist on dp m initially mol oh and mol ha or mol oh and mol ha m h ka or with numbers m mol ethanoic acid left mol ethanoate ions ka h or ph pka scores m m and m m ph log or allow henderson hasselbach ph pka log if either mol acid in mixture or mol salt wrong max for m and m any mention of h max for m and m not if no subtraction so mol ethanoic acid in buffer original mol ph scores for m and m if h used ph scores for m and m chem unit kinetics equilibria and organic chemistry june c ii in ph values penalise fewer than sig figs each time but allow more than dp for values above allow sfs do not insist on dp m xs mol koh m oh m h to or poh m ph if no subtraction max for correct use of volume no subtraction and no use of volume scores zero if wrong subtraction or wrong moles can only score m and m for process mark for dividing their answer to m by correct volume method mark if no volume or wrong volume or multiplied by volume max for m and m process mark for kw divided by their answer to m if poh route give one mark for poh allow sf but not if no subtraction and no use of volume ph scores zero if no subtraction max for correct use of volume cm ph scores if volume not used ph gets if multiplied by vol ph gets

Question 1 2 3 4 5 6 7 8

Topics to revise

AQA > Physical chemistry > Acid base equilibria >

6 Buffer solutions

AQA > Physical chemistry > Acid base equilibria >

1 Bronsted-Lowry theory and pH

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Acid base equilibria >

3 Weak acids

AQA > Organic Chemistry > Carboxylic acids and derivatives >

2 Esterification and hydrolysis of esters

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