Although aldehydes are easily oxidisable, propanal can conveniently be prepared by oxidation of propanol by acidified potassium dichromate. Why ?

Explanation

Aldehydes can be obtained in quantitative yield by the oxidation of primary alcohols provided these are removed from the reaction mixture as soon as they are formed to prevent their further oxidation to carboxylic acids.
Since alehydes having boilng points less than 373K (b.p. of `H_(2)O`) can be easily removed by distillation, therefore, propanal (b.p. 323K) can be easily prepared from propanonl-1 by distilling it from the alcohol-acid dichromate solution.