What is combustion? Write a definition

Write an equation of combustion for the following alcohols:• Ethanol• Methanol• Propanol

• Combustion – The process of burning by reacting a fuel with oxygen

• C2H5OH (l) + 3O2 (g)2CO2 (g) + 3H2O (l)• CH3OH (l) + 1½O2 (g)CO2 (g) + 2H2O (l)• C3H7OH (l) + 4½O2 (g)3CO2 (g) + 4H2O (l)

Oxidation of Alcohols

Oxidation of Alcohols

• Primary and secondary alcohols can be oxidised using an oxidising agent.

• Suitable oxidising agent is a solution containing acidified dichromate ions

H+ /Cr2O72-

• During the reaction, the acidified potassium dichromate changes colour from orange to green.

• Alcohols fall into different classes depending on how the -OH group is positioned on the chain of carbon atoms

• In a primary (1°) alcohol, the carbon which carries the -OH group is only attached to one alkyl group.

• In a secondary (2°) alcohol, the carbon with the -OH group attached is joined directly to two alkyl groups

Primary Alcohols

• On gentle heating with potassium dichromate a primary alcohol can be oxidised to produce an aldehyde.

On stronger heating in excess acidified dichromate alcohol will pass through aldehyde stage to form carboxylic acid.

• Reflux – the continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry.

Secondary and Tertiary Alcohols

• Oxidised by dichromate ions to produce ketones.

• Tertiary alcohols are resistant to oxidation so don’t react.

Ketones can’t be oxidised any further