Summary of tests used to distinguish between aldehydes and ketones.

Aldehydes are readily oxidised to carboxylic acids but ketones are not readily oxidised. 

Aldehydes -------> Carboxylic Acid

Reagent: Potassium Dichromate

Condition: Warm and under reflux

Equation: RCHO + [O] ------> RCOOH

i.e. CH₃CHO +[O] ---> CH₃COOH

Observation: orange solution turns green.

(note: when synthesising an aldehyde in a lab through oxidation of a primary alcohol the aldehyde is quickly removed in order to avoid further oxidation which would result in the formation of a carboxylic acid). 

Ketones CAN'T be oxidised…