If in acid one or all hydrogen atoms are replaced by another cation, then such a chemical substance is called a 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 anion. All salts formed by metals that belong to group Ia of the periodic table are soluble. As for salts formed by Group IIa metals, their solubility changes.
There are medium ones if all the hydrogen in the polybasic acid molecule is replaced by another cation, as well as acid salts, if along with metal or ammonium cations there is a positively charged hydrogen. An example of medium salts is:
- magnesium sulfate MgSO4;
- aluminum sulfate Al2 (SO4) 3;
- ammonium phosphate (NH4) 3PO4;
- sodium carbonate Na2CO3.
Dissociation of medium salts occurs on the positive metal cations and negative anions of the acid residue. The name of the middle salt comes from the name of the acid and the cation of its generators.
Acid salts are formed as a result of the incomplete substitution of hydrogen for a metal or ammonium group. Thus, they are composed of metal, hydrogen and an acid residue. Their formation is possible only for polybasic acids. Examples of such compounds:
- sodium bicarbonate NaHCO3;
- sodium dihydrogen phosphate NaH2PO4;
- sodium hydrogen phosphate Na2HPO4;
- potassium hydrosulfate KHSO4.
Their name contains the prefixes βhydro-β (in the presence of one unsubstituted hydrogen cation) or βdihydro-β (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 types of positive cations (metal and hydrogen ions): NaHSO4 β Na + + H + + SO4Λ Λ. 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 (for example, bicarbonates), the solution will be neutral or even alkaline, i.e. a pH of at least 7.
If middle salts can be obtained as a result of the interaction of the metal with acid and other methods, then the preparation of acid salts is based on the interaction with excess:
polybasic acid with a medium salt. So sodium hydrosulfate is obtained: H2SO4 + Na2SO4 β 2NaHSO4, water-soluble ammonium hydrogen phosphate (NH4) 2HPO4: H3PO4 + 2NH3 β (NH4) 2HPO4 or calcium hydrogen carbonate: CO2 + CaCO3 + H2O β Ca (HCO3) 2;
polybasic acid with alkali. For example, the production of barium dihydrogen phosphate is based on the reaction equation: 2H3PO4 + Ba (OH) 2 β Ba (H2PO4) 2 + 2H2O. By acting on acid salts with alkali, since they are products of incomplete neutralization, one can again obtain a middle salt;
acid oxide with alkali, so get calcium bicarbonate: 2CO2 + Ca (OH) 2 β Ca (HCO3) 2.
It is known that bicarbonates do not exist for the elements to the right of group IIa in the periodic table, and solid bicarbonates are obtained only for the group of elements Ia.
Salts are widely used in various industries, but there are no general 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.
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: they treat various structures to protect them from fire. Also (NH4) 2HPO4 is used as an additive in the manufacture of certain types of cigarettes.
Sodium hydrosulfite NaHSO3 is used for whitening various materials and in photography.
Calcium hydrosulfite Ca (HSO3) 2 is a valuable raw material for the production of wood pulp.
Bisulfites, which are acid salts of sulfuric acid H2SO3, are part of the epinephrine preparation, and are also used in molecular biology.
Potassium hydrosulfates KHSO4 and sodium NaHSO4 are used as flux in non-ferrous metallurgy.
Sodium bicarbonate NaHCO3 is a substance best known from acid salts. It is produced in Sterlitamak (at the Soda enterprise) according to the technical conditions set forth in GOST 2156-76. Sodium bicarbonate is used in food, chemical, pharmaceutical industries, in medicine and in everyday life.