Sodium Hydroxide (Caustic Soda) (NaOH) — Properties, Uses & Safety

Overview

Sodium hydroxide (NaOH), commonly known as caustic soda or lye, is one of the most important strong bases in chemistry and industry. With a molar mass of 40.00 g/mol, it is a white, waxy solid at room temperature that is highly hygroscopic (absorbs moisture from the air) and extremely soluble in water. When dissolved, it dissociates completely into Na⁺ and OH⁻ ions, producing a strongly alkaline solution that is slippery to the touch and highly corrosive. The dissolution of NaOH in water is highly exothermic, releasing significant heat — a property that students can observe safely in controlled demonstrations. Sodium hydroxide is produced industrially by the chlor-alkali process, which involves the electrolysis of sodium chloride brine (2 NaCl + 2 H2O → 2 NaOH + Cl2 + H2). This process simultaneously produces chlorine gas and hydrogen gas, making it one of the most important industrial electrochemical processes. Global NaOH production exceeds 70 million tons per year. The applications of sodium hydroxide are remarkably diverse. It is essential in soap and detergent manufacturing (saponification of fats and oils), pulp and paper production (the kraft process), textile processing (mercerization of cotton), petroleum refining, aluminum production (the Bayer process for extracting alumina from bauxite), water treatment, and food processing (curing olives, making pretzels, peeling fruits). In the home, NaOH is the active ingredient in many drain cleaners and oven cleaners, where it dissolves grease and organic blockages. Safety is a critical concern with sodium hydroxide. It is extremely corrosive and can cause severe chemical burns to skin, eyes, and mucous membranes. Contact with the eyes can cause permanent blindness. GHS pictograms include the corrosion symbol. Proper personal protective equipment (goggles, gloves, lab coat) is essential when handling NaOH. For chemistry students, sodium hydroxide is fundamental to understanding strong base behavior, neutralization reactions (NaOH + HCl → NaCl + H2O), titration techniques (it is the most common titrant for acid-base titrations), saponification reactions, the pH scale, and industrial electrochemistry. The neutralization of NaOH with various acids is one of the most performed experiments in chemistry education, teaching students about stoichiometry, molarity, and indicator color changes.

IUPAC Name

sodium hydroxide

CAS Number

1310-73-2

PubChem CID

14798

Molecular Formula

NaOH

Molar Mass

39.997 g/mol

State at STP

solid

Appearance

White pellets or flakes; highly hygroscopic