Edexcel IGCSE Chemistry alcohols

Practise alcohol questions by completing formula tables, comparing ethanol manufacture methods and explaining fermentation conditions.

Exam points

Complete alcohol tables with formulae, names and relative formula masses.
State hydration conditions for ethanol, including pressure and phosphoric acid catalyst.
Explain fermentation temperature and absence of air using yeast, enzymes and oxidation.

Covered syllabus points

4.29C Alcohol functional group 4.30C Alcohol structures and names 4.31C Oxidation of ethanol 4.32C Manufacture of ethanol 4.33C Fermentation conditions

[Maximum number: 9]

Alcohols contain the functional group - OH

(a)

Give the structural formula of the alcohol that contains one carbon atom.

[ 1 ]

$\mathrm{CH}_{3} \mathrm{OH}$

IGNORE displayed
formula

1
grad

(b)

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is an alcohol that can be obtained from glucose $\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)$ .

[ 5 ]

(i)

Name the process that converts glucose into ethanol.

[ 1 ]

(ii)

Explain why this process is carried out in the absence of air and at a temperature below $40^{\circ} \mathrm{C}$ .

[ 4 ]

Explanation including four from

M1 fermentation/reaction/respiration needs to be anaerobic

M2 because in air / aerobic conditions ethanol not produced

M3 because in air / aerobic conditions $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ are produced

M4 (if temperature above $40^{\circ} \mathrm{C} /$ too high) enzymes (in yeast) become denatured/lose their structure OWTTE

M5 causing fermentation/reaction to slow down /stop

ALLOW M1 in air ethanol would react with oxygen / be oxidised

M2 in air ethanol would form ethanoic acid /carboxylic acid/vinegar

4
exp

(c)

The table gives information about some organic compounds in the same homologous series.

Table for Question (c) — Edexcel IGCSE Chemistry

[ 3 ]

(i)

Complete the table by giving the missing information.

[ 3 ]

Figure for Answer to Question (i) — Edexcel IGCSE Chemistry

M2 $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2}$

M3 butanoic acid

3
grad

[Maximum number: 5]

Ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , can be manufactured from ethene and steam using a phosphoric acid catalyst.

(a)

State the temperature and pressure used in this manufacturing process.
temperature
pressure

[ 2 ]

(b)

Draw the displayed formula of ethanol.

[ 1 ]

(c)

Ethanol burns in a plentiful supply of air to form carbon dioxide and water.

[ 2 ]

(i)

Give the chemical equation for this reaction.

[ 2 ]

$\ce{C2H5OH + 3O2 -> 2CO2 + 3H2O}$

Marking guidance:
- 1 mark for all formulae correct.
- 1 mark for balancing correct formulae.

Allow:
- $\ce{C2H6O}$ for ethanol

Accept:
- multiples and fractions

Ignore:
- state symbols, even if incorrect

[Maximum number: 7]

Some cars in Brazil use ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , as a fuel instead of petrol.
The ethanol is made by the fermentation of glucose which is obtained from sugar cane.
The sugar is extracted from the sugar cane and then dissolved in water to make a sugar solution.

(a)

Name the substance that is added to the sugar solution that causes glucose to ferment.

[ 1 ]

(b)

Which temperature is the most suitable for fermentation?

$0^{\circ} \mathrm{C}$

$10^{\circ} \mathrm{C}$

$30^{\circ} \mathrm{C}$

$80^{\circ} \mathrm{C}$

[ 1 ]

(c)

Explain why fermentation is done in the absence of air.

[ 2 ]

An explanation using either of the following linked pairs:

M1 oxygen in the air would react with ethanol

M2 to form ethanoic acid

OR

M1 the fermentation/reaction/respiration needs to be anaerobic

M2 ethanol would not be formed / $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ would form

ACCEPT ethanol would be oxidised

ALLOW to form carboxylic acid

ALLOW to form vinegar

(d)

Ethanol is also manufactured by reacting steam with ethene, $\ce{C2H4}$ .

The equation for this reaction is:
$\ce{C2H4(g)}$ + $\ce{H2O(g)}$ -> $\ce{C2H5OH(g)}$

State the conditions of temperature and pressure used in this process.

temperature = ................................
pressure = ................................

[ 2 ]

(e)

When ethanol is heated with acidified potassium dichromate(VI), it is oxidised to ethanoic acid.

[ 1 ]

(i)

State the colour change that occurs in the potassium dichromate(VI) during this reaction.

from ................................ to ................................

[ 1 ]

All question bank results loaded

Covered syllabus points

(e) Alcohols question 1

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

Question (i)

(e) Alcohols question 2

Question (a)

Question (b)

Question (c)

Question (i)

(e) Alcohols question 3

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question (i)