It is possible to compare most of the organic compounds that you have covered through simple chemical tests. A number of these tests are covered below.

Test for alkenes

Due to the fact that they undergo electrophilic addition with bromine, alkenes will decolourise bromine water.

To test:

• Add few drops on bromine water to your sample.
• Shake the mixture.
• If:

? the bromine decolourises then an alkene is present.

? the bromine does not decolourise no alkene is present.

Test for haloalkanes

If you heat haloalkanes with dilute sodium hydroxide halide ions are produced due to a nucleophilic substitution reaction.

To test:

• Add aqueous sodium hydroxide to your sample.
• Heat the mixture and then allow it to cool.
• Add dilute nitric acid followed by aqueous silver nitrate.
• If:

? a white precipitate that is soluble in dilute ammonia forms then a chloroalkane was present.

? a cream precipitate that is soluble in concentrated ammonia forms then a bromoalkane was present.

? a yellow precipitate that is insoluble in ammonia forms then an iodoalkane was present.

Test for aldehydes

It is possible to oxidised aldehydes using a mild oxidising agent like Tollen’s reagent or Fehling’s solution.

Tollen’s reagent:

• Add Tollen’s reagent to your sample.
• Heat the mixture.
• If:
• ? a silver mirror forms then an aldehyde is present.

Fehling’s solution:

• Add Fehling’s solution to your sample.
• Heat the mixture.
• If:

? a brick-red precipitate forms an aldehyde is present.

Test for carboxylic acids

Carboxylic acids are able to free carbon dioxide from carbonates.

To test:

• Add sodium carbonate solution to your sample.
• If:

? effervescence is produced and the gas causes the lime water to become milky then a carboxylic acid is present.

Test for acyl chlorides

Chloride ions are released readily by acyl chlorides which produces the gas, hydrogen chloride.

To test:

• Add water slowly to your sample.
• If:

? white, misty fumes are produced then an acyl chloride is present.

Test for amines

Amines are alkaline.

To test:

• Add universal indicator to your sample.
• If:

? it turns blue/purple and has a fishy smell then an amine is present.

Test for alcohols

When sulphuric acid is present, alcohols will react with carboxylic acids to produce esters.

To test:

• Add ethanoic acid followed by sulphuric acid to your sample.
• Heat the mixture.
• If:

? the mixtures begins to smell sweet and fruity then an alcohol was present.

Distinguishing tests for primary, secondary and tertiary alcohols

All react differently when oxidised:

• primary alcohols form aldehydes
• secondary alcohols form ketones
• tertiary alcohols cannot be oxidised

To test:

• Add dilute sulphuric acid and potassium dichromate to your mixture.
• Warm the mixture gently.
• If:

? the mixture turns green than a primary or secondary alcohol is present.

? the mixture does not turn green then a tertiary alcohol is present.

• If the mixture turns green then add Fehling’s mixture and heat again.
• If:

? a brick-red precipitate forms then a primary alcohol was present.

? no brick-red precipitate forms then a secondary alcohol was present.