Potassium hydrogen sulphate, KHSO₄

The primary Potassium hydrogen sulphate, KHSO₄, is formed by the action of an equivalent proportion of sulphuric acid on the normal sulphate or on the nitrate or chloride. It is also produced by the interaction of potassium sulphate and ammonium hydrogen sulphate under the influence of steam superheated at 200° to 400° C.:

K₂SO₄ + NH₄HSO₄ = 2KHSO₄ + NH₃.

When the proportion of steam is deficient, a pyrosulphate is produced.

Potassium hydrogen sulphate is dimorphous, crystallizing in the rhombic and also in the monoclinic system. Its melting-point is given as 200° C. and 210° C., and its mean density as 2.355. The heat of formation from the elements is recorded as 276.1 Cal. And 277.1 Cal.

Solubility of Potassium Hydrogen Sulphate

The solubility in water is given in the table.

Temperature, °C	0	20	40	100
Grams of KHSO4 in 100 grams of water	36.3	51.4	67.3	121.6

The boiling-point of a solution in contact with excess of salt is 108° C. The solution has a very acidic reaction. On heating above the melting-point it is converted into the pyrosulphate.

Several other potassium hydrogen sulphates have been described. Examples of such compounds are K₂SO₄,3H₂SO₄ with melting-point 91.5° C., and K₂SO₄,H₂SO₄ with melting-point 218.6° C.