Used primarily as a catalyst in organic synthesis, especially in the hydration of alkynes to produce carbonyl compounds. It plays a key role in the industrial production of acetaldehyde from acetylene. Also employed in analytical chemistry for the determination of chemical oxygen demand (COD) in water samples, where it binds to chloride ions to prevent interference during oxidation reactions. Historically used in electrochemical cells and as a reference electrode, though this application has declined due to toxicity concerns. Its use is now limited and carefully regulated because of environmental and health risks associated with mercury.