Salt

Malay: Garam · Chinese: 盐

A salt is a compound formed when the hydrogen ion of an acid is replaced by a metal ion or an ammonium ion. This definition ties every salt back to a parent acid: sulfuric acid gives sulfates, hydrochloric acid gives chlorides, and nitric acid gives nitrates, with the acid’s hydrogen swapped for a metal or the ammonium ion, NH₄⁺. Reading a salt’s name tells you which acid and which positive ion it came from.

A worked example makes the replacement visible. In sodium chloride, NaCl, the hydrogen of HCl has been replaced by the sodium ion; in ammonium sulfate, (NH₄)₂SO₄, the two hydrogens of H₂SO₄ are replaced by two ammonium ions. How you prepare a salt depends on its solubility: soluble salts of sodium, potassium and ammonium are made by titration, other soluble salts by reacting an acid with an excess of a metal, base or carbonate and then crystallising, and insoluble salts by precipitation.

The confusion to avoid is the everyday meaning of “salt” as table salt. In chemistry a salt is a whole family of compounds, not just sodium chloride; copper(II) sulfate and lead(II) nitrate are salts too. A second slip is forgetting the ammonium ion counts as the replacing positive ion, so ammonium salts are genuine salts even though they contain no metal at all. Keeping the definition general keeps these cases inside the rule.

Within this chapter the salt is the product that acids, bases, neutralisation and precipitation all lead toward, and its solubility decides the whole preparation method. Our teachers link each salt to its parent acid so naming and preparation become one connected idea rather than two lists.