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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