6 Buffer solutions

 

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Oxford Textbook Pages : 331 - 335

CGP Revision Guide Pages : 92 - 93

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Show Specification Ref : 3.1.12.6

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Question 1 / 5

AQA Jan 2011 Paper 4 Q2 do not write outside the box this question is about the ph of several solutions give all values of ph to decimal places a i write an expression for ph mark a ii calculate the ph of mol dm hydrochloric acid mark a iii calculate the ph of the solution formed when cm of mol dm hydrochloric acid are added to cm of water marks b the acid dissociation constant ka for the weak acid hx has the value x mol dm at c a solution of hx has a ph of calculate the concentration of hx in the solution marks question continues on the next page turn over wmp jan chem do not write outside the box c explain why the ph of an acidic buffer solution remains almost constant despite the addition of a small amount of sodium hydroxide marks d the acid dissociation constant ka for the weak acid hy has the value x mol dm at c a buffer solution was prepared by dissolving mol of the salt nay in cm of a mol dm solution of the weak acid hy d i calculate the ph of this buffer solution marks wmp jan chem do not write outside the box d ii a x mol sample of sodium hydroxide was added to this buffer solution calculate the ph of the buffer solution after the sodium hydroxide was added marks turn over for the next question turn over wmp jan chem
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Question 2 / 5

AQA Jan 2013 Paper 4 Q2 do not write outside the box in this question give all values of ph to decimal places a the ionic product of water has the symbol kw a i write an expression for the ionic product of water mark a ii at oc the value of kw is mol dm calculate the ph of pure water at this temperature marks a iii at oc a mol dm solution of sodium hydroxide has a ph of calculate a value for kw at this temperature marks question continues on the next page turn over wmp jan chem do not write outside the box b methanoic acid hcooh dissociates slightly in aqueous solution b i write an equation for this dissociation mark b ii write an expression for the acid dissociation constant ka for methanoic acid mark b iii the value of ka for methanoic acid is mol dm at oc calculate the ph of a mol dm solution of methanoic acid marks b iv the dissociation of methanoic acid in aqueous solution is endothermic deduce whether the ph of a solution of methanoic acid will increase decrease or stay the same if the solution is heated explain your answer effect on ph explanation marks extra space wmp jan chem do not write outside the box c the value of ka for methanoic acid is mol dm at oc a buffer solution is prepared containing mol of methanoic acid and mol of sodium methanoate in dm of solution c i calculate the ph of this buffer solution at oc marks extra space c ii a cm sample of mol dm hydrochloric acid is added to the buffer solution in part c i calculate the ph of the buffer solution after this addition marks extra space turn over wmp jan chem
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Question 3 / 5

AQA Jun 2011 Paper 4 Q2 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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Question 4 / 5

AQA Jun 2014 Paper 4 Q2 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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Question 5 / 5

AQA Jun 2015 Paper 4 Q9 section b answer all questions in the spaces provided do not write outside the box the acid dissociation constant ka for ethanoic acid is given by the expression h ch coo ka ch cooh the value of ka for ethanoic acid is mol dm at c a a buffer solution is prepared using ethanoic acid and sodium ethanoate in the buffer solution the concentration of ethanoic acid is mol dm and the concentration of sodium ethanoate is mol dm calculate the ph of this buffer solution give your answer to decimal places marks wmp jun chem do not write outside the box b in a different buffer solution the concentration of ethanoic acid is mol dm and the concentration of sodium ethanoate is mol dm a sample of hydrochloric acid containing mol of hcl is added to cm of this buffer solution calculate the ph of the buffer solution after the hydrochloric acid has been added you should ignore any change in total volume give your answer to decimal places marks turn over for the next question turn over wmp jun chem
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