SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE

Sodium hydroxide, Potassium hydroxide
(Sodium hydrate, Potassium hydrate, soda, lye, caustic potash)
CAS 1310-73-2, CAS 1310-58-3

NaOH, KOH

bp 1390 °C, mp 318 °C
bp 1320 °C, mp 360 °C
Highly soluble in water Highly soluble in water (109 g/100 mL)

Odorless Odorless

LD₅₀ oral (rat) LD₅₀ oral (rat)
140 to 340 mg/kg 365 mg/kg

LD₅₀ skin (rabbit) LD₅₀ skin (rabbit)
1350 mg/kg 1260 mg/kg

PEL (OSHA) PEL (OSHA)
2 mg/m³ 2 mg/m ³

TLV (ACGIH) TLV (ACGIH)
2 mg/m³; ceiling 2 mg/m³; ceiling

Extremely corrosive; causes severe burns to skin, eyes, and mucous membranes.

The alkali metal hydroxides are highly corrosive substances; contact of solutions, dusts, or mists with the skin, eyes, and mucous membranes can lead to severe damage. Skin contact with the solid hydroxides or concentrated solutions can cause rapid tissue destruction and severe burns. In contrast to acids, hydroxides do not coagulate protein (which impedes penetration), and metal hydroxide burns may not be immediately painful while skin penetration occurs to produce severe and slow-healing burns. Potassium hydroxide is somewhat more corrosive than sodium hydroxide. Contact with even dilute solutions will also cause skin irritation and injury, the severity of which will depend on the duration of contact. Eye exposure to concentrated sodium hydroxide or potassium hydroxide solutions can cause severe eye damage and possibly blindness. Ingestion of concentrated solutions of sodium hydroxide or potassium hydroxide can cause severe abdominal pain, as well as serious damage to the mouth, throat, esophagus, and digestive tract. Inhalation of sodium/potassium hydroxide dust or mist can cause irritation and damage to the respiratory tract, depending on the concentration and duration of exposure. Exposure to high concentrations may result in delayed pulmonary edema.

Repeated or prolonged contact may cause dermatitis. Sodium hydroxide and potassium hydroxide have not been found to be carcinogenic or to show reproductive or developmental toxicity in humans.

Sodium hydroxide and potassium hydroxide are not flammable as solids or aqueous solutions.

Concentrated sodium hydroxide and potassium hydroxide react vigorously with acids with evolution of heat, and dissolution in water is highly exothermic. Reaction with aluminum and other metals may lead to evolution of hydrogen gas. The solids in prolonged contact with chloroform, trichloroethylene, and tetrachloroethanes can produce explosive products. Many organic compounds such as propylene oxide, allyl alcohol, glyoxal, acetaldehyde, acrolein, and acrylonitrile can violently polymerize on contact with concentrated base. Reaction with nitromethane and nitrophenols produces shock-sensitive explosive salts. Sodium hydroxide and potassium hydroxide as solids absorb moisture and carbon dioxide from the air to form the bicarbonates. Aqueous solutions also absorb carbon dioxide to form bicarbonate. Solutions stored in flasks with ground glass stoppers may leak air and freeze the stoppers, preventing removal.

Sodium hydroxide and potassium hydroxide should be handled in the laboratory using the "basic prudent practices" described in Chapter 5.C. In particular, splash goggles and impermeable gloves should be worn at all times when handling these substances to prevent eye and skin contact. Operations with metal hydroxide solutions that have the potential to create aerosols should be conducted in a fume hood to prevent exposure by inhalation. NaOH and KOH generate considerable heat when dissolved in water; when mixing with water, always add caustics slowly to the water and stir continuously. Never add water in limited quantities to solid hydroxides. Containers of hydroxides should be stored in a cool, dry location, separated from acids and incompatible substances.

In cases of eye contact, immediate and continuous irrigation with flowing water for at least 15 min is imperative. Prompt medical consultation is essential. In case of skin contact, immediately remove contaminated clothing and flush affected area with large amounts of water for 15 min and obtain medical attention without delay. If sodium hydroxide or potassium hydroxide is ingested, do not induce vomiting; give large amounts of water and transport to medical facility immediately. If dusts or mists of these compounds are inhaled, move the person to fresh air and seek medical attention at once.

In many localities, sodium/potassium hydroxide may be disposed of down the drain after appropriate dilution and neutralization. If neutralization and drain disposal is not permitted, excess hydroxide and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.