OCR A Level Chemistry A (H432) Chemistry B
(H433)
PAG 6: Synthesis of an organic solid
This resource includes exam questions from both Chemistry A and Chemistry B. It is not designed as a
topic test but is instead intended as a document to support the teaching and learning of Module 1 –
Development of practical skills in chemistry.
1. A solid organic compound can be purified by recrystallisation.
Which statement(s) about recrystallisation is/are true?
1 The organic compound is more soluble in hot solvent.
2 The hot solution is cooled before the purified organic compound is collected.
3 The melting point of the purified organic compound is lower than the impure compound.
A 1, 2 and 3
B Only 1 and 2
C Only 2 and 3
D Only 1
[1]
Your answer
2. When are insoluble impurities removed during recrystallisation?
A when the hot solution is filtered
B as the solution cools
C when the crystals are filtered off
D when the crystals are washed
Your answer [1]
Created in 1 © OCR
ExamBuilder 2020
, OCR A Level Chemistry A (H432) Chemistry B
(H433)
PAG 6: Synthesis of an organic solid
2(a). Benzoic acid, C6H5COOH, is added to some foods as a preservative.
A student prepares benzoic acid as outlined below.
The student mixes 4.00 cm3 of phenylmethanol, C6H5CH2OH, (density = 1.04 g
cm−3) with
Step 1 sodium carbonate and aqueous potassium manganate(VII), as an oxidising
agent. The mixture is heated under reflux.
The resulting mixture is cooled and then acidified with concentrated HCl .
Step 2 Impure crystals of benzoic acid appear.
Step 3 The student recrystallises the impure crystals to obtain 1.59 g of pure benzoic acid.
In Step 1, sodium carbonate, Na2CO3, makes the reaction mixture alkaline.
Write an ionic equation to show how carbonate ions form an alkaline solution in water.
[1]
(b). In Step 2, explain why the mixture must be acidified so that crystals of benzoic acid appear.
[1]
(c). Write the overall equation for the preparation of benzoic acid from phenylmethanol.
Use [O] for the oxidising agent.
[1]
(d). Calculate the percentage yield of benzoic acid.
Give your answer to 3 significant
figures.
percentage yield =.......................................................% [3]
(e). In Step 3, describe how the student can recrystallise the impure crystals to obtain
pure benzoic acid.
Created in 2 © OCR
ExamBuilder 2020
, OCR A Level Chemistry A (H432) Chemistry B
(H433)
PAG 6: Synthesis of an organic solid
[2]
Created in 3 © OCR
ExamBuilder 2020
(H433)
PAG 6: Synthesis of an organic solid
This resource includes exam questions from both Chemistry A and Chemistry B. It is not designed as a
topic test but is instead intended as a document to support the teaching and learning of Module 1 –
Development of practical skills in chemistry.
1. A solid organic compound can be purified by recrystallisation.
Which statement(s) about recrystallisation is/are true?
1 The organic compound is more soluble in hot solvent.
2 The hot solution is cooled before the purified organic compound is collected.
3 The melting point of the purified organic compound is lower than the impure compound.
A 1, 2 and 3
B Only 1 and 2
C Only 2 and 3
D Only 1
[1]
Your answer
2. When are insoluble impurities removed during recrystallisation?
A when the hot solution is filtered
B as the solution cools
C when the crystals are filtered off
D when the crystals are washed
Your answer [1]
Created in 1 © OCR
ExamBuilder 2020
, OCR A Level Chemistry A (H432) Chemistry B
(H433)
PAG 6: Synthesis of an organic solid
2(a). Benzoic acid, C6H5COOH, is added to some foods as a preservative.
A student prepares benzoic acid as outlined below.
The student mixes 4.00 cm3 of phenylmethanol, C6H5CH2OH, (density = 1.04 g
cm−3) with
Step 1 sodium carbonate and aqueous potassium manganate(VII), as an oxidising
agent. The mixture is heated under reflux.
The resulting mixture is cooled and then acidified with concentrated HCl .
Step 2 Impure crystals of benzoic acid appear.
Step 3 The student recrystallises the impure crystals to obtain 1.59 g of pure benzoic acid.
In Step 1, sodium carbonate, Na2CO3, makes the reaction mixture alkaline.
Write an ionic equation to show how carbonate ions form an alkaline solution in water.
[1]
(b). In Step 2, explain why the mixture must be acidified so that crystals of benzoic acid appear.
[1]
(c). Write the overall equation for the preparation of benzoic acid from phenylmethanol.
Use [O] for the oxidising agent.
[1]
(d). Calculate the percentage yield of benzoic acid.
Give your answer to 3 significant
figures.
percentage yield =.......................................................% [3]
(e). In Step 3, describe how the student can recrystallise the impure crystals to obtain
pure benzoic acid.
Created in 2 © OCR
ExamBuilder 2020
, OCR A Level Chemistry A (H432) Chemistry B
(H433)
PAG 6: Synthesis of an organic solid
[2]
Created in 3 © OCR
ExamBuilder 2020
