Alkalies

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Alkalies or Alkalis (Arabic al-qili, “ashes of the saltwort plant”), originally the hydroxides and carbonates of potassium and sodium, leached from plant ashes. The term now applies to the corresponding compounds of ammonium, NH4, and the other alkali metals and to the hydroxides of calcium, strontium, and barium. All of these substances produce hydroxide ions, OH-, when dissolved in water. The carbonates and ammonium hydroxide give only moderate concentrations of hydroxide ions and are termed mild alkalis. The hydroxides of sodium and potassium, however, produce hydroxide ions in high enough concentration to destroy flesh; for this reason they are called caustic alkalis. Solutions of alkalis turn red litmus blue, react with and neutralize acids, feel slippery, and are electrical conductors.

Caustic soda, or sodium hydroxide, NaOH, is an important commercial product, used in making soap, rayon, and cellophane; in processing paper pulp; in petroleum refining; and in the manufacture of many other chemical products. Caustic soda is manufactured principally by electrolysis of a common salt solution, with chlorine and hydrogen as important by-products.

Sodium carbonate, Na2CO3, one of the mild alkalis, is manufactured from natural deposits or made from common salt brines by the Solvay process. It is used in the manufacture of glass and as a cleaning agent and water softener.