IGCSE Chemistry 4.31C Carbohydrates Topic Practice

Know that ethanol can be oxidised by:

• burning in air or oxygen (complete combustion)

• reaction with oxygen in the air to form ethanoic acid (microbial oxidation)

• heating with potassium dichromate(VI) in dilute sulfuric acid to form ethanoic acid

[Maximum number: 1]

Methanol, ethanol, propanol and butanol are alcohols. They are all liquids that evaporate easily when warmed.

A student uses this apparatus to compare the time taken for the four liquids to evaporate.

She uses this method.
- pour some methanol into an evaporating basin
- place the evaporating basin on top of a beaker containing hot water
- measure the time taken for the methanol to evaporate completely
- repeat the experiment with each of the other alcohols, using the same apparatus

State why it is not safe to heat the evaporating basin directly with a Bunsen flame.

[Maximum number: 3]

This question is about alcohols, carboxylic acids and their reactions.

(a)

Ethanol can be oxidised to produce a carboxylic acid.

[ 3 ]

(i)

Give the names of the two reagents used in this oxidation reaction.

1

2

[ 2 ]

(ii)

Which of these colour changes occurs during the reaction?

green to orange

orange to green

red to yellow

yellow to red

[ 1 ]

[Maximum number: 3]

This question is about the reactions of ethanol and ethanoic acid.

(a)

Ethanol reacts with potassium dichromate(VI) to form ethanoic acid.

Name the other reagent needed in this reaction.

[ 1 ]

(b)

State the colour change that occurs when ethanol reacts with potassium dichromate(VI).
from to

[ 2 ]

[Maximum number: 2]

This question is about alcohols, carboxylic acids and esters.

(a)

Ethanol can be oxidised to ethanoic acid by heating with potassium dichromate(VI) and another reagent.

[ 2 ]

(i)

Name the other reagent.

[ 1 ]

(ii)

State the colour change that occurs during this reaction.
from to

[ 1 ]

[Maximum number: 3]

Methanol, $\mathrm{CH}_{3} \mathrm{OH}$ , is the first member of the homologous series of alcohols.

(a)

Methanol is heated with potassium dichromate(VI) and one other reagent.

The methanol is oxidised to methanoic acid, HCOOH

[ 3 ]

(i)

Give the formula of the other reagent.

[ 1 ]

(ii)

Give the colour change that occurs during the reaction.
from to

[ 2 ]

[Maximum number: 3]

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)

Write a chemical equation for the complete combustion of ethanol in air.

[ 2 ]

(b)

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 ]

[Maximum number: 3]

Ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , is a member of the homologous series of alcohols.

(a)

When ethanol is heated with potassium dichromate(VI) and one other reagent, the ethanol is oxidised to ethanoic acid, $\mathrm{CH}_{3} \mathrm{COOH}$

[ 3 ]

(i)

Give the formula of the other reagent.

[ 1 ]

(ii)

State the colour change that occurs during this oxidation reaction.

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

[ 2 ]

(a)

Ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , can be oxidised to produce ethanoic acid, $\mathrm{CH}_{3} \mathrm{COOH}$ , by heating it with potassium dichromate(VI).

[ 2 ]

(i)

Name one other reactant needed for this reaction to occur.

[ 1 ]

(ii)

Which colour change occurs during this reaction?

colourless to green

green to orange

orange to colourless

orange to green

[ 1 ]

0 selected

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