[fran008]

What do aldehydes have that ketones dont to be able to make them easily oxidised?

[FeLiXe]

Aldehydes are C=O groups at the end of the chain. They can be oxidized to carboxylic acids.

Ketones are C=O groups in the middle of the chain and can't be oxidized without destroying the molecule.

The reason is that for the carboxy-group you need three bonds (2 to O and 1 to OH). That means there is only one more bond left to form with C. If you have ketone with two bonds to other carbon molecules you don't have another possibility to form the third bond.

[movies]

Basically, you have a C-H bond on the carbonyl group in one, but only C-C bonds in the other.  Compare the bond energies!