AQA A-LEVEL CHEMISTRY PAPER 2 ACTUAL EXAM WITH 100%
RATED CORRECT REAL EXAM QUESTIONS AND CORRECT
ANSWERS| GRADED A+ |2025 LATEST VERSION | 100% VERIFIED
This question is about ketones.
(a) Solution X reacts with liquid ketones to form a crystalline solid.
This reaction can be used to identify a ketone if the crystalline solid is
separated, purified by recrystallisation, and the melting point determined.
Describe how the crystalline solid is separated and purified. (5) - (answer)filter / decant
dissolve in minimum vol
of hot solvent
cool / leave (to crystallise) AND filter (under reduced pressure)
Wash with cold solvent/water, and dry (with method)
Suggest a reason, other than safety, why KCN is used instead of HCN. - (answer)HCN weak /
[CN−] too low ORA
allow KCN dissociates to provide CN-/nucleophile
allow KCN dissociates better/more than HCN
Explain why NaBH4 reduces 2-methylbutanal but has no reaction with
2-methylbut-1-ene. - (answer)- H- ion / nucleophile is attracted to δ+ C
- electron rich C=C
- H- ion / nucleophile is repelled by C=C
OR
C=C only attacked by/reacts with electrophiles
,Explain how the structure of ethanal leads to the formation of two isomers. - (answer)1. planar
(around) carbonyl / C=O
2. (equal chance of) attack from each side (by CN-)
Suggest a suitable reagent and conditions for the conversion of 2-hydroxypropanenitrile into
acrylonitrile. - (answer)conc H2SO4 or conc H3PO4
heat / 170°C
Describe how you would distinguish between separate samples of the two stereoisomers of
CH3CH2CH2CH2CH(OH)CN - (answer)(plane) polarised light
Enantiomers would ROTATE light in opposite directions
Explain why the reaction produces a racemic mixture. - (answer)PLANAR carbonyl group
Attack from either side With EQUAL probability OR produces equal amounts (of the two
isomers/enantiomers)
By considering the mechanism of the reaction, explain why the product has no effect on plane
polarised light. - (answer)Stage 1: Formation of product
Nucleophilic attack
Planar carbonyl group
H - attacks from either side (stated or drawn)
Stage 2: Nature of product
Product of step 1 shown
This exists in two chiral forms (stated or drawn)
Equal amounts of each enantiomer / racemic mixture formed
Stage 3: Optical activity
Optical isomers / enantiomers rotate the plane of polarised light equally in
, With a racemic / equal mixture the effects cancel
Describe what happens when a reaction mixture is refluxed and why it is necessary, in this case,
for complete oxidation to ethanoic acid. - (answer)A mixture of liquids is heated to boiling point
for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into liquid and
returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised
Full equation for oxidation of ethanal to ethanolic acid - (answer)3CH3CHO + Cr2O72- + 8H+ 3
CH3CO2H + 4H2O + 2Cr3+
Use these data to describe how you would obtain a sample of ethanal from a mixture of these
three compounds. Include in your answer a description of the apparatus you would use and how
you would minimise the loss of ethanal. Your description of the apparatus can be either a
description in words or a labelled sketch. - (answer)Mixture heated in a suitable flask / container
A labelled sketch illustrating these points scores the marks With still head containing a
thermometer
Water cooled condenser connected to the still head and suitable cooled collecting vessel
Collect sample at the boiling point of ethanal
Cooled collection vessel necessary to reduce evaporation of ethanal
Use your knowledge of structure and bonding to explain why it is possible to separate ethanal in
this way. - (answer)Hydrogen bonding in ethanol and ethanoic acid or no hydrogen bonding in
ethanal
Intermolecular forces / dipole-dipole are weaker than hydrogen bonding
State the reason for inverting the flask several times - (answer)To ensure the solution is
homogeneous
Justify why a smaller target titre would not be appropriate - (answer)
RATED CORRECT REAL EXAM QUESTIONS AND CORRECT
ANSWERS| GRADED A+ |2025 LATEST VERSION | 100% VERIFIED
This question is about ketones.
(a) Solution X reacts with liquid ketones to form a crystalline solid.
This reaction can be used to identify a ketone if the crystalline solid is
separated, purified by recrystallisation, and the melting point determined.
Describe how the crystalline solid is separated and purified. (5) - (answer)filter / decant
dissolve in minimum vol
of hot solvent
cool / leave (to crystallise) AND filter (under reduced pressure)
Wash with cold solvent/water, and dry (with method)
Suggest a reason, other than safety, why KCN is used instead of HCN. - (answer)HCN weak /
[CN−] too low ORA
allow KCN dissociates to provide CN-/nucleophile
allow KCN dissociates better/more than HCN
Explain why NaBH4 reduces 2-methylbutanal but has no reaction with
2-methylbut-1-ene. - (answer)- H- ion / nucleophile is attracted to δ+ C
- electron rich C=C
- H- ion / nucleophile is repelled by C=C
OR
C=C only attacked by/reacts with electrophiles
,Explain how the structure of ethanal leads to the formation of two isomers. - (answer)1. planar
(around) carbonyl / C=O
2. (equal chance of) attack from each side (by CN-)
Suggest a suitable reagent and conditions for the conversion of 2-hydroxypropanenitrile into
acrylonitrile. - (answer)conc H2SO4 or conc H3PO4
heat / 170°C
Describe how you would distinguish between separate samples of the two stereoisomers of
CH3CH2CH2CH2CH(OH)CN - (answer)(plane) polarised light
Enantiomers would ROTATE light in opposite directions
Explain why the reaction produces a racemic mixture. - (answer)PLANAR carbonyl group
Attack from either side With EQUAL probability OR produces equal amounts (of the two
isomers/enantiomers)
By considering the mechanism of the reaction, explain why the product has no effect on plane
polarised light. - (answer)Stage 1: Formation of product
Nucleophilic attack
Planar carbonyl group
H - attacks from either side (stated or drawn)
Stage 2: Nature of product
Product of step 1 shown
This exists in two chiral forms (stated or drawn)
Equal amounts of each enantiomer / racemic mixture formed
Stage 3: Optical activity
Optical isomers / enantiomers rotate the plane of polarised light equally in
, With a racemic / equal mixture the effects cancel
Describe what happens when a reaction mixture is refluxed and why it is necessary, in this case,
for complete oxidation to ethanoic acid. - (answer)A mixture of liquids is heated to boiling point
for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into liquid and
returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised
Full equation for oxidation of ethanal to ethanolic acid - (answer)3CH3CHO + Cr2O72- + 8H+ 3
CH3CO2H + 4H2O + 2Cr3+
Use these data to describe how you would obtain a sample of ethanal from a mixture of these
three compounds. Include in your answer a description of the apparatus you would use and how
you would minimise the loss of ethanal. Your description of the apparatus can be either a
description in words or a labelled sketch. - (answer)Mixture heated in a suitable flask / container
A labelled sketch illustrating these points scores the marks With still head containing a
thermometer
Water cooled condenser connected to the still head and suitable cooled collecting vessel
Collect sample at the boiling point of ethanal
Cooled collection vessel necessary to reduce evaporation of ethanal
Use your knowledge of structure and bonding to explain why it is possible to separate ethanal in
this way. - (answer)Hydrogen bonding in ethanol and ethanoic acid or no hydrogen bonding in
ethanal
Intermolecular forces / dipole-dipole are weaker than hydrogen bonding
State the reason for inverting the flask several times - (answer)To ensure the solution is
homogeneous
Justify why a smaller target titre would not be appropriate - (answer)
