Caustic Soda, caustic, alkali, and lye are all common names for sodium hydroxide (NaOH). It is a strong base that is extremely soluble in water and dissociates into sodium and hydroxyl ions in solution.

Applications
Caustic Soda is used to maintain or increase pH. Increasing pH with caustic soda precipitates magnesium (Mg2+) and suppresses calcium (Ca2+) in high-hardness waters such as seawater. It also reduces corrosion and neutralizes acid gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S).