Bases, hydrates of oxides, hydroxides, hydroxides (the most common name for reagents is hydroxide) are complex substances formed as a result of compounding a basic oxide with water, for example, KOH, NaOH, Ba (OH) 2, Fe (OH) 3. The base molecule consists of a metal atom and one or more OH hydroxyl groups, the number of which corresponds to the oxidation state (electrochemical valency) of the metal.
In aqueous solutions, bases dissociate into positively charged metal ions (cations) and negatively charged ions - hydroxyl groups (anions). The chemical properties of the bases are due to the presence of negatively charged OH- hydroxyl ions in them.
The bases of alkali and alkaline earth metals are solids soluble in water. Aqueous solutions of bases are soapy to the touch, stain the red litmus test with blue color, corrode paper, leather and other materials.
Water-soluble bases are called alkalis , and potassium and sodium hydroxides are called caustic alkalis .

Most basic oxides do not directly interact with water, and their hydroxides are obtained by the action of an alkali or ammonia solution on a solution of the corresponding salt. These bases are also solid colored substances, practically insoluble in water.
Application. The base group is the smallest in the assortment of chemicals and barely reaches two dozen items. However, the importance of this group is enormous due to the presence of sodium and potassium hydroxides in it and an aqueous solution of ammonia, without which it is practically impossible to imagine any chemical process or scientific research. Let us dwell in more detail on some of them.
Sodium hydroxide, caustic soda NaOH - a white crystalline substance, floating in the air. Goes on sale
in the form of uneven pieces, sticks, scales or small hemispherical particles. Caustic soda is widely used in analytical chemistry, organic and inorganic synthesis. In analytical practice, it is used for a variety of purposes: neutralizing the acid, determining the elements that give insoluble hydroxides, for preparing titrated solutions, Kjeldahl nitrogen analysis, determining organic and inorganic acids, and in many other cases.
Potassium hydroxide, potassium hydroxide KOH - a white crystalline hygroscopic substance. Available in the form of pieces, sticks, granules or flakes. Potassium hydroxide is widely used in synthetic works for the preparation of potassium salts and carrying out technological processes that provide better results than with caustic soda. In analytical chemistry, KOH is used to absorb acidic vapors and gases, neutralize acidic solutions, saponify esters, titrimetric determination of acids, in gas and organic analysis, etc. Caustic potassium is also used in cases where caustic soda is undesirable.
Potassium hydroxide, like sodium hydroxide, is a caustic substance that acts on the skin and mucous membranes in a cauterizing manner. Even the smallest amounts of alkali in the eyes are especially dangerous.
Ammonium hydroxide, aqueous ammonia NH4OH , is available as a 25% aqueous solution. It is used to neutralize and in the synthesis of various organic and inorganic substances. In analytical chemistry, it is used to precipitate hydrates of oxides of various metals, to obtain soluble ammonia, used to determine certain elements, etc.
In addition to the three most important hydroxides listed above, hydrates of aluminum, barium, bismuth, iron, calcium, lithium, / copper, cobalt, beryllium, chromium and other elements are also known in synthesis and analytical practice.
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