organic analysis

How can aldehydes be distinguished from ketones using Tollen’s reagent?

Tollen’s reagent contains Ag⁺ ions. Aldehydes reduce Ag⁺ to metallic silver, forming a silver mirror. Ketones do not react.

How can Fehling’s solution be used to test for aldehydes?

Aldehydes reduce Fehling’s solution from blue to a red precipitate of Cu₂O. Ketones give no change.

What does a positive test with acidified potassium dichromate indicate?

Orange dichromate (Cr₂O₇²⁻) is reduced to green Cr³⁺ when oxidising primary or secondary alcohols or aldehydes. No change for ketones or tertiary alcohols.

What is the test for a carboxylic acid?

Carboxylic acids react with carbonates (e.g. Na₂CO₃) to produce CO₂, which turns limewater cloudy. Effervescence confirms acid presence.

How can bromine water be used to test for unsaturation?

Alkenes decolorise orange bromine water in an electrophilic addition reaction, indicating a C=C bond.