Sodium Hydroxide

Overview

Sodium hydroxide, also known as caustic soda and caustic soda, has the chemical formula NaOH. It is a highly corrosive, strong base, typically present as white flakes or granules. It is miscible with water to form an alkaline solution and is also soluble in methanol and ethanol. This alkaline substance is deliquescent and absorbs water vapor from the air, as well as acidic gases such as carbon dioxide. Sodium hydroxide is a commonly used chemical. It has a wide range of applications and is essential in many industrial processes: it is commonly used in the manufacture of wood pulp paper, textiles, soaps, and other detergents, and is also used in household alkaline drain cleaning products.

Properties

Pure anhydrous sodium hydroxide is a white, translucent, crystalline solid. It is highly corrosive and hygroscopic, making it useful as a desiccant. However, it cannot dry out sulfur dioxide, carbon dioxide, or hydrogen chloride gases. It is also deliquescent in air. Sodium hydroxide is highly soluble in water, and its solubility increases with increasing temperature. Dissolution releases a significant amount of heat, with a saturated solution concentration of 16.4 mol/L (1:1) at 288K. Its aqueous solution has an astringent and greasy taste and is strongly alkaline, possessing all the properties of an alkali. Caustic soda is commercially available in both solid and liquid forms. Pure solid caustic soda is white and brittle, coming in blocks, flakes, rods, and granules. Pure liquid caustic soda is a colorless, transparent liquid. Sodium hydroxide is also readily soluble in ethanol and glycerin, but insoluble in ether, acetone, and liquid ammonia. It is corrosive to fibers, skin, glass, and ceramics, releasing heat when dissolved or when a concentrated solution is diluted. Neutralization reactions with inorganic acids also generate significant heat, producing the corresponding salts. Reactions with metals such as aluminum and zinc, and non-metals such as boron and silicon release hydrogen. It undergoes disproportionation reactions with halogens such as chlorine, bromine, and iodine. It can precipitate metal ions from aqueous solutions as hydroxides and saponify oils and fats to produce the corresponding sodium salts of organic acids and alcohols, which is the principle behind its use in removing oil stains from fabrics.

Applications

Sodium hydroxide has a wide range of uses. In chemical experiments, in addition to being used as a reagent, it can also be used as an alkaline desiccant due to its strong hygroscopicity. Caustic soda is widely used in the national economy and is required by many industrial sectors. Chemical manufacturing is the largest consumer, followed by papermaking, aluminum smelting, tungsten smelting, rayon, artificial cotton, and soap manufacturing. Large quantities of caustic soda are also used in the production of dyes, plastics, pharmaceuticals, organic intermediates, recycling of used rubber, sodium metal production, water electrolysis, and inorganic salt production, including the production of borax, chromium salts, manganates, and phosphates. Industrial sodium hydroxide should comply with national standards GB209-2006; industrial ion exchange membrane sodium hydroxide should comply with national standards GB/T11199-89; chemical fiber sodium hydroxide should comply with national standards GB11212-89; and edible sodium hydroxide should comply with national standards GB5175-85. In industry, sodium hydroxide is often referred to as caustic soda, also known as caustic soda or caustic soda. This is because concentrated sodium hydroxide solutions can corrode the epidermis and cause burns if splashed onto the skin. It dissolves proteins and is highly irritating and corrosive (due to its protein-dissolving properties, alkali burns are more difficult to heal than acid burns). A 0.02% solution instilled into rabbit eyes can cause corneal epithelial damage. The intraperitoneal LD50 in mice is 40 mg/kg, and the oral LDLo in rabbits is 500 mg/kg. Dust irritates the eyes and respiratory tract and corrodes the nasal septum. Splashes on the skin, especially mucous membranes, can form soft crusts and penetrate deep tissues, leaving scars. Splashes into the eyes can damage not only the cornea but also deep tissues, leading to blindness in severe cases. Accidental ingestion can cause digestive tract burns, colic, mucosal erosions, vomiting of bloody gastric contents, bloody diarrhea, and sometimes hoarseness, dysphagia, shock, digestive tract perforation, and, in later stages, gastrointestinal stenosis. Due to its strong alkalinity, it can pollute water bodies, so care should be taken against plant and aquatic life.