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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
Reactivity and Incompatibility
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.
Storage and Handling
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. For more information on disposal procedures, see Chapter 7 of this volume.