Organic Chemistry: Carboxylic Acids (Edexcel International A Level Chemistry)

Exam Questions

1a
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2 marks

This question is about an ester, Y, with the molecular formula C8H16O2.

Y contains 66.7% carbon, 11.1% hydrogen and 22.2% oxygen by mass. Show that these data are consistent with its molecular formula.

1b3 marks

The structure of compound Y is

q17b-paper-4-2021-june-edexcel-ial-chemistry

i)
Give the IUPAC name of Y.
(2)

ii)
Draw the structures of two organic compounds that would react together to form Y.
(1)
1c4 marks

The high resolution proton NMR spectrum of compound Y was obtained.

i)
Label the three remaining hydrogen environments B, C and D on the structure.

(1)

q17c-paper-4-2021-june-edexcel-ial-chemistry

ii)
Complete the table.
(3)
Hydrogen
environment
Splitting pattern
of peak
Relative
peak area
A triplet 3
B    
C    
D    

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1a3 marks

This question is about carboxylic acids and their derivatives.

Lactic acid, CH3CH(OH)COOH, is produced in muscles as a result of anaerobic respiration.

i)
The structure of lactic acid is

q17a-paper-4-jan-2021-edexcel-ial-chemistry

Give a reason why lactic acid shows optical isomerism.

(1)

ii)
A laboratory sample of lactic acid does not rotate the plane of plane-polarised monochromatic light.

Give a reason for this observation.

(1)

iii)
Give the structure of the organic product formed when lactic acid reacts with concentrated phosphoric(V) acid, H3PO4.

(1)

1b3 marks

A reaction scheme involving butanoic acid is shown.

q17b-paper-4-jan-2021-edexcel-ial-chemistry

Identify X, Y and Z by name or formula.

Alcohol X
Reagent Y
Compound Z
1c2 marks

The repeat unit of a polyester is shown.

q17c-paper-4-jan-2021-edexcel-ial-chemistry

Give the structures of the two monomers that could form this polyester.

Monomer 1

Monomer 2

1d6 marks

An organic compound E contains carbon, hydrogen and oxygen only.

i)

The accurate relative atomic masses, Ar , of the three elements in E are shown in the table.

Element Ar
hydrogen 1.0078
carbon 12.0000
oxygen 15.9949

E contains five carbon atoms and gives a molecular ion peak at m / z = 102.0678 in its mass spectrum.

Deduce the molecular formula of E.

(1)

ii)
Aqueous sodium hydrogencarbonate is added to a sample of E.
No effervescence occurs.

State what can be deduced by this observation.
(1)
iii)
The infrared spectrum of E has an absorption in the range 1750 – 1735 cm−1.

Name the functional group in E.
(1)
iv)
Data from the high resolution proton NMR spectrum of E is shown.

Peak

Chemical shift, straight delta

/ ppm for TMS

Splitting pattern Relative peak area
A 4.02 triplet 2
B 2.05 singlet 3
C 1.65 sextet 2
D 0.95 triplet 3

Deduce the structure of E.

Justify your answer by labelling the protons responsible for each peak.

(3)

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