methods of preparations of aldehydes n ketones???
The oxidising agent used in these reactions is normally a solution of sodium or potassium dichromate(VI) acidified with dilute sulphuric acid. If oxidation occurs, the orange solution containing the dichromate(VI) ions is reduced to a green solution containing chromium(III) ions.
The net effect is that an oxygen atom from the oxidising agent removes a hydrogen from the -OH group of the alcohol and one from the carbon to which it is attached.
R and R' are alkyl groups or hydrogen. If at least one of these groups is a hydrogen atom, then you will get an aldehyde. If they are both alkyl groups then you get a ketone.