Sodium bisulfate

Sodium bisulfate, also sodium hydrogen sulfate, has the chemical formula NaHSO4. The anhydrous form is hygroscopic. Its melting point is poorly defined because it begins to decompose into sodium pyrosulfate and water before it reaches its melting points.

Solutions of sodium bisulfate are acid, with a 1M solution having pH of 1.4. In some applications, such solutions can be used instead of sulfuric acid solution. For example, from a solution of sodium bisulfate and sodium acetate it is possible to distill acetic acid. Sodium bisulfate solutions will also liberate CO2 from most carbonates.

Sodium bisulfate behaves, to some degree, as if it were a complex of sodium sulfate with sulfuric acid. This is evident if either the anhydrous form or the monohydrate come in contact with ethanol, which causes them to separate into those two components.

Production
Sodium bisulfate is produced by two methods. One method involves mixing stoichiometric quantities of sodium hydroxide and sulfuric acid which react to form sodium bisulfate and water.

NaOH + H2SO4 → NaHSO4 + H2O

A second production method involves reacting sodium chloride (salt) and sulfuric acid at elevated temperatures to produce sodium bisulfate and hydrogen chloride gas.

NaCl + H2SO4 → NaHSO4 + HCl

The liquid sodium bisulfate is sprayed and cooled so that it forms a solid bead. The hydrogen chloride gas is dissolved in water to produce hydrochloric acid as a useful byproduct of the reaction.

The product of commerce is anhydrous. The only producer in the USA, Jones Hamilton Company, uses the sulfuric acid/sodium chloride process, which produces anhydrous product.

Uses

 * Household cleaners, Sani-Flush, for example (roughly 45%)
 * Silver pickling
 * To reduce alkalinity and pH in swimming pools
 * In pet foods
 * As a preservative for soil and water samples in analytical laboratory analysis