The simplest answer to your question is this...aqueous KOH is generally used for reactions that are not water sensitive and when performing a hydrolysis. Saponification of amides and esters are two examples when aqueous KOH is preferred (since these are hydrolysis reactions). Alternatively, KOH is used in 'anhydrous' form such as in ethanolic KOH (KOH dissolved in ethanol) when reactions are water sensitive or when performing a dehydration reaction. This is because the water added to a dehydration reaction will shift the equilibrium of that reaction towards the left (i.e., the starting materials). Aldol condensations are one such example, especially when the target compound is the conjugated enone (formed by dehydration of the intermediate beta-hydroxyketone). This is because the dehydration reaction rate is decreased in the prescense of water (shifts equilibrium of the reaction towards the starting materials)...

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The simplest answer to your question is this...aqueous KOH is generally used for reactions that are not water sensitive and when performing a hydrolysis. Saponification of amides and esters are two examples when aqueous KOH is preferred (since these are hydrolysis reactions). Alternatively, KOH is used in 'anhydrous' form such as in ethanolic KOH (KOH dissolved in ethanol) when reactions are water sensitive or when performing a dehydration reaction. This is because the water added to a dehydration reaction will shift the equilibrium of that reaction towards the left (i.e., the starting materials). Aldol condensations are one such example, especially when the target compound is the conjugated enone (formed by dehydration of the intermediate beta-hydroxyketone). This is because the dehydration reaction rate is decreased in the prescense of water (shifts equilibrium of the reaction towards the starting materials)...

https://uk.answers.yahoo.com/question/index?qid=20081016073719AAGARO3

Also if the substrate is alkyl halide then alcoholic KOH is better for elimination reactions and aqueous KOH for substitutions.

I thing in organic chemistry , firstly you must ask some question;

what I want to do ?  after you may research.

Alcoholic KOH produces more stronger nuclephile CH3O- than alcoholic one.

In alcoholic solution the KOH is basic enough (pKa 15.74) to deprotonate a small amount of alcohol molecules (pKa 16–17)), thus forming alcohlate salts ROK. The alcoholate anions RO− are not only more basic than pure OH− but they are also bulkier (how much bulkier depends on the group R). The higher bulkiness makes RO− a worse nucleophile than OH− and the higher basicity makes it better at E2 eliminations.

Thanks to all

The question of the general assembly, and thanks for all

Alcoholic KOH is more strong base, than aqueous. It is used for preparation alkenes from alkyl halides. But always exist a competition between nucleophile substitution and elimination reactions.

alc. KOH is used for elimination reaction of alkyl halide to form alkene while aq. KOH is used for substitution of alkyl halide to alcohol.

Alc. KOH is used as a base and aq. KOH is used as a nucleophile specific with akyl halide.

Anup is absolutely right in alcohols hydroxide acts as a strong base and hence abstract the beta hydrogen for elimination reactions while in aqueous phase hydroxide acts as a nucleophile.  Lets see the other phase of these reactions in hydrolysis reaction there is sidewise formation of alcohols hence the use of alcohol as solvent in these reactions will shift the equilibrium to backward side i.e. ester but using water as solvent and distilling out the alcohol will push the equilibrium in forward direction. Similarly in dehydration reactions water is formed as side product and the removal of water will take the reaction to forward direction hence it is always carried out in alcohols.

What will be the pH of alcoholic and aqueous solution of KOH .

Alkoholic KOH means OC2H5 K, this means strong base as u know reaction of alchols with alkali metals or their hydroxides give alkoxides, consequently alkoxides gives alkenes on reaction with  alkyl halides  specially sec. while aqueous KOH reslts alchols on reactions with alkyl halides.