Acid Salts

If in an acid one or all of the hydrogen atoms are replaced by another cation, then such a chemical is called salt. The metal or ammonium group in such a molecule always has a positive oxidation state and is called a cation. The acid residue is called the anion. All salts formed by metals that belong to group Ia of the Periodic Table of Mendeleev are soluble. As for the salts formed by the metals of group IIa, their solubility changes.

There are averages if all the hydrogen in the polybasic acid molecule is replaced by another cation, as well as acid salts, if along with the metal or ammonium cations there is positively charged hydrogen. Examples of medium salts are:

- magnesium sulfate MgSO4;

- Aluminum sulphate Al2 (SO4) 3;

- ammonium phosphate (NH4) 3PO4;

- sodium carbonate Na2CO3.

The dissociation of the average salts occurs on the positive metal cations and the negative anions of the acid residue. The name of the average salt comes from the name of the acid and the cation of its generators.

Acidic salts are formed as a result of incomplete replacement of hydrogen by a metal or an ammonium group. Thus, they consist of metal, hydrogen and acid residue. Their formation is possible only for polybasic acids. Examples of such compounds are:

Sodium bicarbonate NaHCO3;

Sodium dihydrogen phosphate NaH2PO4;

- sodium hydrogenphosphate Na2HPO4;

- potassium hydrogen sulfate KHSO4.

In the title there are prefixes "hydro-" (in the presence of one unsubstituted hydrogen cation) or "dihydro-" (in the presence of two unsubstituted hydrogen cations).

In aqueous solutions, acid salts dissociate into negative anions in the form of acid residues, as well as into two kinds of positive cations (ions of metal and hydrogen): NaHSO4 ↔ Na + + H + + SO4ˉ . In the hydrolysis of acid salts formed by strong acids, the aqueous solution has a pH of less than 7, hence the name of these salts. In the hydrolysis of acid salts derived from weak acids (eg, hydrocarbonates), the solution will be neutral or even alkaline, i.e., a pH of at least 7.

If the average salts can be obtained as a result of the interaction of the metal with the acid and other methods, the production of acid salts is based on interaction with the excess:

• Polybasic acid with an average salt. Thus, sodium hydrogen sulphate is obtained: H2SO4 + Na2SO4 → 2NaHSO4, water-soluble ammonium hydrogen phosphate (NH4) 2HPO4: H3PO4 + 2NH3 → (NH4) 2HPO4 or calcium hydrogen carbonate: CO2 + CaCO3 + H2O → Ca (HCO3) 2;

• Polybasic acid with alkali. For example, the basis for the production of barium dihydrogen phosphate is the reaction equation: 2H3PO4 + Ba (OH) 2 → Ba (H2PO4) 2 + 2H2O. By reacting to acidic salts with alkali, since they are products of incomplete neutralization, it is possible to obtain again the middle salt;

• Acid oxide with alkali, so the calcium bicarbonate is obtained: 2CO2 + Ca (OH) 2 → Ca (HCO3) 2.

It is known that bicarbonates do not exist for elements standing in the periodic table to the right of group IIa, and solid hydrocarbonates are obtained only for a group of elements Ia.

Salts are widely used in various industries, but there are no common directions for their use, since everything is individual. The use of this type of salt depends on the properties of the chemical compound and is determined by economic feasibility.

Thus, for example, ammonium hydrogen phosphate (NH4) 2HPO4 is used as a complex phosphorus-ammonium fertilizer in agriculture. In addition, this compound is used in the fight against fires: for protection from fire, they handle various structures. Also (NH4) 2HPO4 is used as an additive in the production of certain types of cigarettes.

Sodium hydrosulfite NaHSO3 is used for bleaching various materials and in photography.

Calcium hydrosulfite Ca (HSO3) 2 is a valuable raw material for the production of cellulose from wood.

Bisulfites, which are acidic salts of sulfurous acid H2SO3, are part of the drug epinephrine, and are also used in molecular biology.

Potassium hydrosulfates KHSO4 and sodium NaHSO4 are used as a flux in non-ferrous metallurgy.

Sodium Hydrocarbonate NaHCO3 is a substance most known from acid salts. It is produced in the city of Sterlitamak (at the enterprise "Soda") under the technical conditions set out in GOST 2156-76. Sodium bicarbonate is used in the food, chemical, pharmaceutical industry, in medicine and at home.