AQA Jun 2016 Paper 4 Q1 (with explained solutions) |

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AQA Jun 2016 Paper 4 Q1

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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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mark scheme a level chemistry chem june answers mark additional comments guidance must show allow ch co h ch co ignore state symbols ignore allow ch co h ch co h ch c oh question a ch cooh h o ch coo h o or ch cooh ch coo h b ch cooh hno ch cooh no id detail of c i marked with c ii c ii marked with c i new hno h m h mol dm m ph log m or m mol naoh m excess mol h subtraction of m from moles of hno or conseq from c i m h m or m ph log m or mark scheme a level chemistry chem june or new hno mol hno total vol must be dp allow correct ph conseq to their h concentration m allow ecf for subtraction of mol if no subtraction no further marks m if no use of volume no further marks ph if incorrect volume used can score m m allow must be dp of d i m ka m m m h ph coo cooh h ch ch h ch cooh ka or with numbers or with ha sodium ethanoate m h s alt acid ch ch or m coo cooh ka h m electronegative chlorine withdraws electrons stabilises reduces charge on coo or weakens o h bond m m or makes o h more polar g d ii d iii e mark scheme a level chemistry chem june penalise once here not h a ha if ka expression wrong allow correct ph conseq to their h concentration m only mark for answer must be dp allow correct ph conseq to their h concentration ph can score m m and m ignore formula allow sodium acetate accept or if m incorrect ce inclusion of in calculation can only score m ignore units x gives allow cl has negative inductive effect ignore chloroethanoic acid dissociates more readily mark independently of

Question 1 2 3 4 5 6 7 8 9

Topics to revise

AQA > Physical chemistry > Acid base equilibria >

3 Weak acids

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 >

6 Buffer solutions

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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