Chloroethane is treated with alcoholic potassium hydroxide. The product formed is;

•  Chloroethane reacts with alc.KOH to form ethene. 
• It is a basic method for the preparation of alkene.
•  Alcoholic $\mathrm{KOH}$ when used the elimination reaction takes place. 
• Following is the reaction that takes place;

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}+\text{ alc. }\mathrm{KOH}\to {\mathrm{C}}_2{\mathrm{H}}_4+\mathrm{HCl}$