Testing reagent= Acidified solution of potassium dichromate (VI). The alcohol is added and the mixture is heated.
For a primary alcohol- the mixture changes from orange (Cr2O72-) to green (Cr3+) and the product is an aldehyde.
Secondary alcohol – the mixture changes from orange (Cr2O72-) to green (Cr3+) and the product is a ketone.
Tertiary alcohol – no reaction. The mixture stays orange.