Organic chemistry IIEdexcel A-Level Chemistry: Topic test

20 questions, 54 marks

Edexcel A-Level Chemistry

Organic chemistry II topic test

Total 54 marks

Name

Class

Date

1
2-Methylbutanoic acid, CH₃CH₂CH(CH₃)COOH, is found in some fruits and can also be made in the laboratory. A solution of one pure enantiomer of the acid in ethanol rotates the plane of plane-polarised monochromatic light by +8.4° in a polarimeter.
(a)
How many chiral centres are there in one molecule of 2-methylbutanoic acid?
[1 mark]
A0
B1
C2
D3
(b)
The other enantiomer of the acid is dissolved in ethanol at the same concentration and measured in the same polarimeter tube. What rotation is observed?
[1 mark]
A−8.4°
B+8.4°
C0°
D+4.2°
(c)
A chemist makes 2-methylbutanoic acid in a reaction that produces no optical activity, even though every molecule of the product is chiral. Explain this observation.
[2 marks]
Total for question 1: 4 marks
2
Compound Z has the molecular formula C₅H₁₀O. It gives an orange precipitate with 2,4-dinitrophenylhydrazine solution, gives no reaction with Tollens' reagent, and forms a pale yellow precipitate when warmed with iodine in the presence of sodium hydroxide solution.
(a)
Which conclusion can be drawn from the result with 2,4-dinitrophenylhydrazine alone?
[1 mark]
AZ is an aldehyde
BZ is a ketone
CZ contains a carbonyl group, C=O
DZ contains a carboxylic acid group
(b)
Which compound is Z?
[1 mark]
APentanal
BPentan-3-one
C2-Methylbutanal
DPentan-2-one
(c)
The orange precipitate is filtered off, purified and its melting temperature measured. Explain how this result can be used to confirm the identity of Z.
[2 marks]
Total for question 2: 4 marks
3
Butanoic acid, CH₃CH₂CH₂COOH, has a sharp, unpleasant smell and is present in rancid butter. A chemist plans to make it from 1-bromopropane in two steps.
(a)
State the reagent and conditions for each step of the route and name the intermediate compound formed.
[3 marks]
(b)
In one experiment, 12.3 g of 1-bromopropane ( $M_\mathrm{r}$ = 123.0) gave 5.28 g of butanoic acid ( $M_\mathrm{r}$ = 88.0). Calculate the percentage yield of butanoic acid, and give one reason why the yield is less than 100%.
[4 marks]
Total for question 3: 7 marks
4
Butanone, CH₃COCH₂CH₃, reacts with hydrogen cyanide in the presence of a small amount of potassium cyanide to form a hydroxynitrile. The isolated product does not rotate the plane of plane-polarised monochromatic light, even though its molecules contain a chiral centre.
(a)
Describe the mechanism of this reaction, stating the role of the potassium cyanide and where each curly arrow starts and finishes.
[6 marks]
(b)
Explain why the product mixture has no effect on plane-polarised light, using the structure of the product and the shape of the carbonyl group.
[6 marks]
Total for question 4: 12 marks
5
Propanoyl chloride, CH₃CH₂COCl, is a colourless liquid used to make esters and amides. In a laboratory it is added, separately and with care, to a series of compounds containing –OH or –NH groups.
(a)
Which compound reacts with propanoyl chloride to form N-methylpropanamide, CH₃CH₂CONHCH₃?
[1 mark]
AMethanol
BAmmonia
CWater
DMethylamine
(b)
Which statement about the reaction of propanoyl chloride with methanol is correct?
[1 mark]
AIt forms methyl propanoate and hydrogen chloride
BIt forms propanoic acid and chloromethane
CIt forms methyl propanoate and water, and is reversible
DIt needs concentrated sulfuric acid and heating
(c)
Propanoyl chloride reacts with an excess of concentrated ammonia. Write the equation for the reaction and name the organic product.
[2 marks]
Total for question 5: 4 marks
6
Methyl butanoate, CH₃CH₂CH₂COOCH₃, has a fruity smell and is used as a flavouring. A technician hydrolyses a sample by heating it under reflux with aqueous sodium hydroxide.
(a)
Which pair of compounds is formed in the hydrolysis with aqueous sodium hydroxide?
[1 mark]
AButanoic acid and methanol
BSodium methanoate and propan-1-ol
CSodium butanoate and methanol
DSodium butanoate and methanoic acid
(b)
The technician repeats the hydrolysis using dilute sulfuric acid instead of sodium hydroxide. Which statement is correct?
[1 mark]
AThe acid-catalysed reaction goes to completion, whereas alkaline hydrolysis is reversible
BThe acid-catalysed reaction is reversible and forms butanoic acid, not its salt
CThe acid-catalysed reaction forms propan-1-ol and methanoic acid
DThe acid-catalysed reaction needs no heating
(c)
After the alkaline hydrolysis, dilute hydrochloric acid is added until the mixture is acidic before butanoic acid can be obtained. Explain why this step is needed, including an ionic equation.
[2 marks]
Total for question 6: 4 marks
7
Nylon-6,10 is a polyamide used to make toothbrush bristles. It is made from decanedioic acid, HOOC(CH₂)₈COOH ( $M_\mathrm{r}$ = 202.0), and 1,6-diaminohexane, H₂N(CH₂)₆NH₂ ( $M_\mathrm{r}$ = 116.0).
(a)
Give the structural formula of the repeat unit of nylon-6,10, name the type of polymerisation and name the small molecule eliminated.
[3 marks]
(b)
A chemist makes 28.2 g of nylon-6,10 from the two monomers, assuming 100% yield. The relative formula mass of the repeat unit is 282.0. Calculate the mass of decanedioic acid required and the mass of water eliminated.
[4 marks]
Total for question 7: 7 marks
8
A materials chemist makes a polyester by reacting hexanedioyl dichloride, ClCO(CH₂)₄COCl, with butane-1,4-diol, HO(CH₂)₄OH. An earlier method made the same polyester from hexanedioic acid and butane-1,4-diol. The polyester can be broken down by hot aqueous sodium hydroxide and by hot dilute hydrochloric acid.
(a)
Compare the two methods of making the polyester, including the repeat unit and the small molecule eliminated in each.
[6 marks]
(b)
Predict the organic products of the complete hydrolysis of the polyester by (i) hot aqueous sodium hydroxide and (ii) hot dilute hydrochloric acid. Explain why the products differ and why one of these hydrolyses may not go to completion.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).