The treatment of alkyl chloride with aqueous KOH leads to the formation of alcohols but in the presence of alcoholic KOH, alkenes are the major products. Explain why?

Answer : In aqueous solution, KOH is ionised into K⁺ and OH⁻. OH⁻ being a nucleophile leads to nucleophilic substitution reaction with alkyl chlorides to form alcohols. Moreover, the OH⁻ ions in aqueous solution are highly hydrated. This reduces the basic character of OH⁻ ions which, therefore, fail to remove hydrogen from β-carbon to form an alkene.

An alcoholic solution of KOH, on the other hand, contains alkoxide (RO⁻) ions that are much stronger base than OH⁻ ions; hence, alcoholic solution of KOH preferentially eliminates a molecule of HCl from an alkyl chloride to form an alkene.