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Reactions with salts

Sulfuric acid reacts with most bases to give the corresponding sulfate or bisulfate.

Sulfuric acid reacts with sodium chloride, and gives hydrogen chloride gas and sodium bisulfate:

Aluminium sulfate, also known as paper maker's alum, is made by treating bauxite with sulfuric acid:

Sulfuric acid can also be used to displace weaker acids from their salts. Reaction with sodium acetate, for example, displaces acetic acid, CH COOH, and forms sodium bisulfate:

Similarly, treating potassium nitrate with sulfuric acid produces nitric acid.

When combined with nitric acid, sulfuric acid acts both as an acid and a dehydrating agent, forming the nitronium ion NO + 2, which is important in nitration reactions involving electrophilic aromatic substitution. This type of reaction, where protonation occurs on an oxygen atom, is important in many organic chemistry reactions, such as Fischer esterification and dehydration of alcohols.

When allowed to react with superacids, sulfuric acid can act as a base and can be protonated, forming the ion. Salts of have been prepared (e.g. trihydroxyoxosulfonium hexafluoroantimonate(V)) using the following reaction in liquid HF:

The above reaction is thermodynamically favored due to the high bond enthalpy of the Si–F bond in the side product. Protonation using simply fluoroantimonic acid, however, has met with failure, as pure sulfuric acid undergoes self-ionization to give ions:

which prevents the conversion of H SO to by the HF/ SbF system.