4.5 Alcohols

REVISION NOTES

IGCSE Edexcel Chemistry

4.5 Alcohols

4.5.1C Know that alcohols contain the functional group −OH

The functional group of alcohol is -OH

– O – H

4.5.2C Understand how to draw structural and displayed formulae for methanol, ethanol, propanol (propan-1-ol only) and butanol (butan-1-ol only), and name each compound
the names propanol and butanol are acceptable

4.5.3C 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

OXIDATION OF ETHANOL

Ethanol undergoes oxidation in three different ways

1. Complete combustion

Burning in air or oxygen

ethanol + O2 → CO2 + H2O

2. Microbial oxidation

ethanol + oxygen in the air → ethanoic acid

3. Ethanol and potassium dichromate(VI)

With heat
With dilute sulfuric acid

ethanol + potassium dichromate(VI) → ethanoic acid

4.5.4C Know that ethanol can be manufactured by:

Reacting ethene with steam in the presence of a phosphoric acid catalyst
At a temperature of about 300^oC and a pressure of about 60–70 atm
The fermentation of glucose, in the absence of air, at an optimum temperature of about 30^oC and using the enzymes in yeast

Manufacture of Ethanol

1. Ethene + steam

Catalyst: phosphoric acid
Temperature: 300oC
Pressure: 60-70 atm

Features

Continuous process
Produces very pure ethanol
Comes from non-renewable sources, ethene extracted from crude oil

ethanol + potassium dichromate(VI) → ethanoic acid

2. Fermentation of glucose

Absence of air (anaerobic)
Optimum temperature of about 30oC
Using the enzymes in yeast

Features

Batch process
Produces impure ethanol, so must be distilled
Comes from renewable sources such as glucose from plants

glucose → ethanol + carbon dioxide

4.5.5C Understand the reasons for fermentation, in the absence of air, and at an optimum temperature

Fermentation of Glucose

glucose → ethanol + carbon dioxide

Why is the optimum temperature around 25 to 50^oC?
- If too low: yeast that is used would be inactive
- If too high: enzymes in yeast would be denatured / would no longer function
Why must air be kept out (absence of oxygen)?
- If there is air: ethanol would be oxidised to ethanoic acid