Alkynes undergo hydration when warmed with water in the presence of mercuric sulphate ($\text{HgSO}_4$) and dilute sulphuric acid ($\text{H}_2\text{SO}_4$) at $333\text{ K}$ to form carbonyl compounds. The addition of water follows Markovnikov's rule. While the hydration of ethyne (a 2-carbon alkyne) yields ethanal (an aldehyde), the hydration of any higher alkyne having more than two carbon atoms (such as propyne, but-1-yne, etc.) yields a ketone. This happens because the nucleophile ($\text{OH}^-$ from water) attaches to the more substituted carbon atom of the triple bond, forming an unstable enol intermediate, which then tautomerizes to form a stable ketone .