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A LevelChemistryCIEExam Questions18. Carboxylic Acids & Derivatives18.2 Esters

Esters (CIE A Level Chemistry)

Exam Questions

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18.2 Esters

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18.2 Esters

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1a3 marks

This question is about esters. 

Complete the table to show how some common esters are formed. 

 Carboxylic Acid  Alcohol   Ester 
ethanoic acid    methyl ethanoate
  ethanol ethyl propanoate
butanoic acid propan-1-ol  

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1b2 marks

All of the esters in part (a) are formed via a condensation reaction. 

State the conditions needed for this reaction.

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1c2 marks

Each of the esters in part (a) can be hydrolysed to reform the carboxylic acid and alcohol. 

Give the reagents and conditions needed for this reaction. 

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1d1 mark

Suggest why esters are used in the manufacture of foods.

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2a2 marks

This question is about carboxylic acids and esters.

Draw the structures of:

i)
3-methylbutanoic acid
[1]
ii)
methyl ethanoate 

[1]

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2b1 mark

2-methylbutanoic acid can be produced by the oxidation of 2-methylbutan-1-ol using acidified K2Cr2O7. 

Give the colour change that would be observed during this reaction. 

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2c1 mark

Name the products formed when methyl ethanoate is hydrolysed under acidic conditions.

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2d4 marks

Methyl ethanoate can also be hydrolysed under alkaline conditions using sodium hydroxide.

i)
Draw the displayed formula of the salt and alcohol formed in this reaction. 

ii)
How is the salt converted into carboxylic acid? 

iii)
Apart from the conditions, and products made, give one other difference between acid and alkaline hydrolysis.

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1a5 marks

Two isomeric compounds are shown below in Fig. 1.1. 

4a-1


Fig. 1.1

 

i)
State the name of each isomer.
[1]

ii)
Suggest a chemical reagent to distinguish between these isomers and deduce the type of reaction taking place.
[2]

iii)
State the observations made in each case.
[2]

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1b3 marks
i)
Compound B, CH3CH(CH3)CH(OH)COOH, can be oxidised into compound C.

Deduce the half-equation for the conversion of compound B into C.

[1]
ii)
The half equation for the oxidation reaction using acidified potassium dichromate(VI) is as follows:

Cr2O72- (aq) + 14H+ (aq) + 6e– → 2Cr3+ (aq) + 7H2O (l)

Deduce the overall redox equation for the conversion of B into C.

[2]

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1c2 marks

The same reaction in part (b) can be used to oxidise ethanol into ethanal or ethanoic acid, depending on the reaction conditions.


Outline how the reaction conditions can be changed to produce ethanal or ethanoic acid.

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1d3 marks

Under the right conditions, the two molecules of compound A can react together to produce a dimer.

i)
Name the type of reaction taking place and state the reaction conditions.
[2]
ii)
Draw the structure of the product, showing clearly how the two molecules are joined.
[1]

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2a
Sme Calculator1 mark

An organic ester, B, has the empirical formula C2H4O. An experiment by a student in a college gave a value of 87.5 for Mr of B.

What is the molecular formula of B?

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2b4 marks

In the boxes below, draw the structural formulae of four isomers of B that are esters.

SDFSDF

W

SDFSDF

X

SDFSDF

Y

SDFSDF

Z

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2c4 marks

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.

A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent. 

i)
What group does the reaction with 2,4-dinitrophenylhydrazine reagent show to be present in D?

[1]

ii)
What does the result of the test with Tollens’ reagent show about D?

[1]

iii)
What is the structural formula of the alcohol C?

[1]

iv)
Which of your esters, W, X, Y, or Z has the same structure as that of the ester B?

[1]

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2d1 mark

Which, if any of your esters, W, X, Y, or Z is chiral? Explain your answer.

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3a4 marks

Esters are compounds which provide the flavour of many fruits and the perfumes of many flowers.

The ester CH3(CH2)2CO2CH3 contributes to the aroma of apples.

i)
State the reagents and conditions needed for the hydrolysis of this ester.

[2]
ii)
Write the equation for the hydrolysis of this ester.

[1]
iii)
Apart from their use as perfumes and food flavourings, state one major commercial use of esters.
[1]

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3b3 marks

Leaf alcohol is a stereoisomer that can form when insects such as caterpillars eat green leaves.

leaf-alcohol-structure

i)
Draw the other stereo-isomer of leaf alcohol.
[1]
ii)
Draw the structure for the ester formed when leaf alcohol reacts with ethanoic acid.

Show all the bonds in the ester group
[2]

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3c3 marks
i)
Deduce the relative molecular mass, Mr, for leaf alcohol.

[1]

ii)
Leaf alcohol was reacted to form a product with an Mr value 18 units less.

Suggest a structure for this product and deduce the type of reaction that took place

structure of product


type of reaction .....................................................
[2]

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3d2 marks

Describe a simple chemical test to distinguish between leaf alcohol and your product in part (c)(ii).

test ...................................................................................................................................


observation ......................................................................................................................

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1a6 marks

Esters have important commercial uses, such as artificial flavourings in food. 

They can be prepared in several ways, including through the reactions of alcohols with carboxylic acids, as well as the carboxylic acid derivatives, acid anhydrides and acyl chlorides.

Ester S, CH3CH2COOCH2CH(CH3)2 is used in rum flavouring. 

Outline how you could obtain a sample of ester S, beginning with a named alcohol and carboxylic acid.
 

Include any essential reaction conditions and write an equation for the reaction. 

You do not need to include details of the separation or purification methods involved. 

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1b4 marks

Ester S can undergo acid or alkaline hydrolysis. 

The products formed depends on the type of hydrolysis that has taken place.

Compare the two types of hydrolysis.

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1c4 marks

A second ester, Ester T is responsible for a raspberry scent and has the molecular formula C5H10O2.

Ester T can be produced by the reaction of an acid with a branched primary alcohol.

Identify the acid and alcohol used to prepare ester T.


Draw and name ester T.

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