Alkalis

Alkalis, water-soluble bases (see), substances that give the hydroxyl ion in aqueous solution. The hydroxyl ion determines the properties of alkalis: 1) they react with acids with the release of heat and formation of salts (neutralization reaction); 2) they cause a change in color of many indicators (red litmus turns blue, colorless phenolphthalein turns bright red, etc.), thanks to which alkalis can be easily detected; 3) they act as catalysts in the hydrolysis of many organic compounds (saponification of fats, hydrolysis of proteins, etc.), and the catalytic activity of alkalis is proportional to the concentration of the hydroxyl ion. The formation of salt-like compounds, as well as hydrolysis reactions, form the basis for the destruction and dissolution of many organic substances by alkalis. The strongest alkalis are the water-soluble hydroxides of alkali metals: Li, Na, K, Rb and Cs, which are almost completely dissociated in aqueous solution. Of these, NaOH and KOH are most common and are known as caustic alkalis due to their strong corrosive action on plant and animal tissues. Ammonium hydroxide and many organic nitrogen-containing compounds, such as amines (see), which react with water similarly to ammonia, belong to the weaker alkalis: R NH₂ + H₂O ⇌ RNH₃OH ⇌ RNH₃⁺ + OH^-. Solutions of many salts formed by a strong base and a weak acid also have alkaline properties; hydroxyl ions appear due to dissociation and interaction with water (see Hydrolysis). Of such salts, sodium carbonate (soda) and potassium carbonate (potash), known as carbonated alkalis, are most widely used as alkalis: Na₂CO₃ ⇌ 2Na⁺ + CO₃^2-; CO₃^2- + H₂O ⇌ HCO₃^- + OH^-. Similar reactions form the basis for the alkaline properties of borax (Na₂B₄O₇·10H₂O), potassium acetate (KC₂H₃O₂), di- and trimetallic salts of phosphoric acid (Na₂HPO₄), and soap (R CO₂Na). Due to their ability to dissolve and destroy protein substances, strong alkalis are used in medicine as irritating, cauterizing, and antiseptic agents. Carbonated alkalis (mainly Natrium bicarbonicum, NaHCO₃, and alkaline mineral waters) are used to neutralize organic acids formed due to abnormal fermentation in the stomach in catarrh, dyspepsia, heartburn; in pathological conditions of the body accompanied by decreased blood alkalinity; in the treatment of gout to dissolve uric acid (Lithium carbonicum, LiCO₃, 0.1-0.2 several times a day, or Lithium salicylicum 0.5-1.0); as a diuretic (Kalium aceticum 0.5-1.0 several times a day); in catarrh of the respiratory tract. Borax (Natrium boricum, s. Borax) is used for rinsing and smearing the mouth in stomatitis. In case of acid poisoning, alkalis (not carbonated) and soap (Sapo medicatus) are administered. A. Kuzin. Occupational hazards from contact with alkalis. Caustic alkalis (KOH, NaOH, NH₄OH) have wide industrial application. They are used in the chemical industry, soap making, for impregnating wood, for cleaning metals (in electroplating), in textile production (bleaching, printing), and in many other fields. Sometimes alkalis are obtained as a by-product, sometimes they act as an impurity in other chemical substances. These alkalis are used mainly in the form of aqueous solutions of various concentrations. Some categories of workers have to deal with solid caustic soda or potash. Ammonia, which is released from NH₄OH, acts as a gas. Depending on concentration, duration of action, and temperature of the solution, NaOH and KOH can cause burns of all degrees. Histologically, in severe cases, there is colliquative necrosis. The eschar formed by the action of alkalis is soft, easily smeared. Such an eschar does not prevent deeper penetration of alkalis into the tissue. This is one of the reasons why burns from concentrated alkalis often cause deeper and more difficult-to-tissue damage than acid burns. Burns from 15% alkalis often result in extensive, massive keloid scars. In industrial settings, burns from alkalis are common. According to Shapiro's data, in the caustic workshop of one enterprise, up to 14 burns per month occur among 40 workers. Acting on abrasions, cracks in working conditions, even moderately concentrated alkalis can cause "cauterizations", painful ulcers of small size, which in foreign literature are called "pigeon eyes" (pigeonneau). In moderate concentrations, alkalis degrease and irritate the skin. The epidermis softens under the action of alkalis. With daily contact with alkalis, the skin becomes dry, cracked; this is most noticeable on the back of the hands. Increased sweating of the palms appears, which at times can even interfere with work. Nails become dull, brittle at the free edge, thin; their surface is covered with grooves (mostly longitudinal). Often the nails take on a saucer-like shape. Changes in the nails due to damage to the matrix sometimes take on a persistent character. New nails grow deformed. The most common clinical form of skin damage from moderately concentrated alkalis in occupational settings is limited to the site of exposure dermatitis. Eczema of the hands when working with alkalis is observed less frequently. Eczemas apparently occur when alkalis act in combination with other harmful factors in everyday life and in production. The degreasing caused by the action of alkalis, their effect on the cells of the horny layer, disrupts the barrier functions of the skin, facilitates the penetration of infection and the action of various other harmful factors, both physical and chemical. Specifically increased sensitivity of the skin to caustic alkalis is hardly observed; such descriptions are not found in the literature. What has been said regarding the effect on the skin of KOH and NaOH can be applied to NH₄OH, however, this alkali is significantly inferior in strength of action to the first two. From the action of concentrated solutions of NH₄OH, dermatitis is more often observed, ulcers are rare. Deep burns under normal conditions are hardly possible. First aid in the workshop for burns with strong alkalis consists of immediate (in the first minute) washing of the affected part of the body with a strong stream of clean water (from the tap). Such immediate washing prevents the development of skin lesions. At the medical station, it is appropriate to apply a dressing with a compress of weak concentration acetic acid solution. Further treatment proceeds according to the general rules of dermatology in accordance with the clinical picture. Prevention of skin lesions with constant contact with alkalis requires first of all thorough washing of residues of alkalis from the hands after work, then greasing them with fatty ointments. It is desirable to wear gloves, as skin that has been exposed to alkalis for a long time is less resistant to atmospheric influences. In enterprises, prevention should be aimed at developing a production process without unprotected skin contact with alkalis. If necessary to work with alkalis, workers should be provided with rubber gloves. Persons suffering from eczema should not be allowed to work with alkalis. V. Vedrov.