Why does SO4 2 not dissolve in acids


Sulfates are salts or esters of sulfuric acid. The salts contain the sulfate ion as an anion[SO4]2−. The esters of sulfuric acid have the general formula R-O-SO2-O-R ', where R and / or R' are organic radicals.


primary and secondary sulfates

The salts of the dibasic acid sulfuric acid (H.2SO4) can be used in primary and secondary sulfates organize. In the case of monovalent cations MI. the sum formulas M applyI.HSO4 and MI.2SO4:

primary sulfates secondary sulfates
Synonyms acid sulfates
Hydrogen sulfates
neutral sulfates
normal sulfates
Examples Sodium hydrogen sulfate, NaHSO4
Calcium hydrogen sulfate, Ca (HSO4)2
Sodium sulfate, Na2SO4
Calcium sulfate, CaSO4

Common names


Sulphate groups as ligands in coordination chemistry can be designated with [Tetraoxosulphato (−2)] or [Sulphato (−2)]. It should be noted that according to the more recent recommendations of the nomenclature, the sulfite group (SO3)2− characterized by the suffix -sulphate and referred to as trioxosulphate or trioxosulphate (IV).

Sulfuric acid ester

Ester the sulfuric acid are occasionally used as well Sulfuric acid ester called. The names of these compounds often end with -sulfate. These esters also include the fatty alcohol sulfates, which are important in terms of application.



Most sulfates are soluble in water. Exceptions are the little or sparingly soluble sulfates of the alkaline earth metals calcium, strontium and barium as well as lead (II) sulfate.

The alkali and alkaline earth sulfates in particular are thermally extremely stable. Sulphates of trivalent metal cations decompose in the heat to the corresponding oxides and sulfur trioxide:

Hydrogen sulfates are known as salts of the alkali metals. They are soluble in water. If the salts are heated, disulfates, i.e. salts of disulfuric acid, are formed.

Anions and pH

Sulfuric acid is a strong biprotonic acid. In a one-molar, aqueous solution of the acid there are almost no H2SO4Molecules, but essentially HSO4-Ions before. Only a good 1% of the HSO4-Ions deprotonate to SO42−. The hydrogen sulfate anion (HSO4) can act as both an acid and a base, so it is amphoteric. The pKS.-The value of the hydrogen sulfate ion is 1.89.

If a hydrogen sulfate salt is dissolved in water, a mixture of hydrogen sulfate and sulfate ions is formed in an equilibrium reaction. Hydrogen sulfates can therefore be used as a medium-strength acid, with the acidity being considerably higher than that of acetic acid (pKS. = 4.76). Due to these properties, hydrogen sulfates can also be used in buffer solutions. The buffer area is in the strongly acidic area. The acidic reaction in water is used, for example, in toilet cleaners


Sulphates are the most important mineral compounds for many metallic elements. Sources of sulphate in the soil are e.g. B. Anhydrite (CaSO4), Plaster (CaSO4 · 2 H2O) and alabaster (CaSO4 · 2 H2O). Biological sources are (bacterial) sulphate formations from sulphide and sulphurous biomass components (e.g. proteins). Sulphates occur in different amounts in groundwater. According to the German Drinking Water Ordinance, a limit value of 240 mg / l applies to the drinking water obtained from it.


Sulphates are detected chemically by adding hydrochloric acid and barium chloride or barium hydroxide solution. This creates a sparingly soluble precipitate of white barium sulfate. The acid is added because other anions such as carbonate or sulfite with barium also form salts which are sparingly soluble in water but which are soluble in acids.


Categories: Fabric Group | sulfate