Aqueous KOH gives alcohols because of substitution reaction. While alcoholic KOH gives alkenes due to elimination reaction.
Alkyl chlorides with Aq.KOH :--
When an alkyl chlorides treated with Aq.KOH in solution KOH is almost ionized to give OH— ions which being a strong nucleophile, brings about a substitution reaction and give alcohols.
Alkyl chlorides with alco.KOH :--
In contrast,an alcoholic solution of KOH contains alkoxide (RO–) ions which being a much stronger base than OH- ions eliminates a mol ecule of HCl from an alkyl chlorides to form alkenes.