1 Bronsted-Lowry theory and pH

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Oxford Textbook Pages : 316 - 321

CGP Revision Guide Pages : 82, 84 - 85

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Show Specification Ref : 3.1.12.1, 3.1.12.2

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Question 1 / 5

January 2013 QP – Unit 4 AQA Chemistry A-level_question_2 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 2 / 5

June 2012 QP – Unit 4 AQA Chemistry A-level_question_3 do not write outside the box a this question is about several br nsted lowry acids and bases define the term br nsted lowry acid mark b three equilibria are shown below for each reaction indicate whether the substance immediately above the box is acting as a br nsted lowry acid a or a br nsted lowry base b by writing a or b in each of the six boxes b i ch cooh h o ch coo h o b ii ch nh h o ch nh oh b iii hno h so h no hso mark mark mark c a cm sample of mol dm hydrochloric acid was placed in a beaker distilled water was added until the ph of the solution was calculate the total volume of the solution formed state the units marks extra space question continues on the next page turn over wmp jun chem do not write outside the box d at k the value of the acid dissociation constant ka for the weak acid hx in aqueous solution is mol dm d i calculate the value of pka for hx at this temperature give your answer to decimal places mark d ii write an expression for the acid dissociation constant ka for the weak acid hx mark d iii calculate the ph of a mol dm solution of hx at this temperature give your answer to decimal places marks extra space wmp jun chem do not write outside the box e an acidic buffer solution is formed when cm of mol dm aqueous sodium hydroxide are added to cm of mol dm aqueous hx the value of ka for the weak acid hx is mol dm calculate the ph of this buffer solution at k give your answer to decimal places marks extra space turn over wmp jun chem
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Question 3 / 5

June 2013 QP – Unit 4 AQA Chemistry A-level_question_3 do not write outside the box a this question is about br nsted lowry acids of different strengths state the meaning of the term br nsted lowry acid mark b i write an expression for the acid dissociation constant ka for ethanoic acid mark b ii the value of ka for ethanoic acid is mol dm at c calculate the concentration of ethanoic acid in a solution of the acid that has a ph of marks c the value of ka for chloroethanoic acid clch cooh is mol dm at c c i write an equation for the dissociation of chloroethanoic acid in aqueous solution mark c ii suggest why chloroethanoic acid is a stronger acid than ethanoic acid marks wmp jun chem d p and q are acids x and y are bases the table shows the strength of each acid and base do not write outside the box acids bases strong weak strong weak the two acids were titrated separately with the two bases using methyl orange as indicator the titrations were then repeated using phenolphthalein as indicator the ph range for methyl orange is the ph range for phenolphthalein is for each of the following titrations select the letter a b c or d for the correct statement about the indicator s that would give a precise end point write your answer in the box provided both indicators give a precise end point only methyl orange gives a precise end point only phenolphthalein gives a precise end point neither indicator gives a precise end point d i acid p with base x d ii acid q with base x d iii acid q with base y question continues on the next page mark mark mark turn over wmp jun chem do not write outside the box using a burette cm of mol dm sulfuric acid were added to a conical flask containing cm of mol dm aqueous sodium hydroxide assume that the sulfuric acid is fully dissociated calculate the ph of the solution formed give your answer to decimal places e marks extra space wmp jun chem
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Question 4 / 5

June 2014 QP – Unit 4 AQA Chemistry A-level_question_2 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

June 2016 QP – Unit 4 AQA Chemistry A-level_question_1 section a answer all questions in the spaces provided do not write outside the box a nitric acid hno is a strong acid ethanoic acid ch cooh is a weak acid write an equation to show how ethanoic acid behaves as a weak acid in its reaction with water mark b when pure ethanoic acid reacts with pure nitric acid ethanoic acid acts as a base write an equation for this reaction mark c two beakers a and b each contain cm of mol dm nitric acid c i calculate the ph of the solution formed after cm of distilled water are added to beaker a give your answer to decimal places marks c ii calculate the ph of the solution formed after cm of mol dm aqueous sodium hydroxide are added to beaker b give your answer to decimal places marks wmp jun chem do not write outside the box d a third beaker c contains cm of mol dm ethanoic acid the acid dissociation constant ka for ethanoic acid has the value mol dm at c d i write an expression for ka for ethanoic acid and use it to calculate the ph of the ethanoic acid solution in beaker c show your working give your answer to decimal places marks ka calculation d ii aqueous sodium hydroxide is added to beaker c until the ph of the solution becomes name the salt formed in the reaction of ethanoic acid with sodium hydroxide mark d iii calculate the value of in the solution with the ph of salt ethanoic acid marks turn over wmp jun chem e explain why chloroethanoic acid is a stronger acid than ethanoic acid do not write outside the box marks f explain why data books do not usually contain values of ka for strong acids marks wmp jun chem
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