In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.
The component ions in a salt compound can be either inorganic, such as chloride (Cl−), or organic, such as acetate (CH
). Each ion can be either monatomic, such as fluoride (F−), or polyatomic, such as sulfate (SO2−
Types of salt
Salts can be classified in a variety of ways. Salts that produce
Solid salts tend to be
Salts exist in many different colors, which arise either from their constituent anions, cations or solvates. For example:
- chromate ion
- dichromate ion
- cobalt nitrate is made red by the chromophore of hydrated cobalt(II) ([Co(H2O)6]2+).
- copper sulfate is made blue by the copper(II) chromophore
- potassium permanganate is made violet by the permanganate anion.
- nickel chloride is typically made green by the hydrated nickel(II) chloride [NiCl2(H2O)4]
- sodium chloride, magnesium sulfate heptahydrate appear colorless or white because the constituent cations and anions do not absorb light in the part of the spectrum that is visible to humans.
Different salts can elicit all five
Salts of strong acids and strong bases ("
Many ionic compounds exhibit significant
Salts are characteristically insulators. Molten salts or solutions of salts conduct electricity. For this reason, liquified (molten) salts and solutions containing dissolved salts (e.g., sodium chloride in water) can be used as electrolytes.
Salts characteristically have high melting points. For example, sodium chloride melts at 801 °C. Some salts with low lattice energies are liquid at or near room temperature. These include molten salts, which are usually mixtures of salts, and ionic liquids, which usually contain organic cations. These liquids exhibit unusual properties as solvents.
The name of a salt starts with the name of the cation (e.g., sodium or ammonium) followed by the name of the anion (e.g., chloride or acetate). Salts are often referred to only by the name of the cation (e.g., sodium salt or ammonium salt) or by the name of the anion (e.g., chloride salt or acetate salt).
Common salt-forming cations include:
- Ammonium NH+
- Calcium Ca2+
- Iron Fe2+
- Magnesium Mg2+
- Potassium K+
- Pyridinium C
- Sodium Na+
- Copper Cu2+
Common salt-forming anions (parent acids in parentheses where available) include:
- Acetate CH
- Carbonate CO2−
3 (carbonic acid)
- Chloride Cl−
- Citrate HOC(COO−)
2 (citric acid
- hydrocyanic acid)
- Fluoride F−
- Nitrate NO−
3 (nitric acid)
- Nitrite NO−
2 (nitrous acid)
- Oxide O2−
- Phosphate PO3−
4 (phosphoric acid)
- Sulfate SO2−
4 (sulfuric acid)
Salts with varying number of hydrogen atoms replaced by cations as compared to their parent acid can be referred to as monobasic, dibasic, or tribasic, identifying that one, two, or three hydrogen atoms have been replaced; polybasic salts refer to those with more than one hydrogen atom replaced. Examples include:
- Sodium phosphate monobasic (NaH2PO4)
- Sodium phosphate dibasic (Na2HPO4)
- Sodium phosphate tribasic (Na3PO4)
Salts are formed by a chemical reaction between:
- A base and an acid, e.g., NH3 + HCl → NH4Cl
- A metal and an acid, e.g., Mg + H2SO4 → MgSO4 + H2
- A metal and a non-metal, e.g., Ca + Cl2 → CaCl2
- An acid and a base anhydride, e.g., 2 HNO3 + Na2O → 2 NaNO3 + H2O
- In the salt metathesis reaction where two different salts are mixed in water, their ions recombine, and the new salt is insoluble and precipitates. For example:
- Pb(NO3)2 + Na2SO4 → PbSO4↓ + 2 NaNO3
Strong salts or strong electrolyte salts are chemical salts composed of strong electrolytes. These ionic compounds dissociate completely in water. They are generally odorless and nonvolatile.
Strong salts start with Na__, K__, NH4__, or they end with __NO3, __ClO4, or __CH3COO. Most group 1 and 2 metals form strong salts. Strong salts are especially useful when creating conductive compounds as their constituent ions allow for greater conductivity.
Weak salts or "weak electrolyte salts" are, as the name suggests, composed of weak electrolytes. They are generally more volatile than strong salts. They may be similar in odor to the acid or base they are derived from. For example, sodium acetate, CH3COONa, smells similar to acetic acid CH3COOH.
- Bresle method (the method used to test for salt presence during coating applications)
- Fireworks/pyrotechnics (salts are what give color to fireworks)
- Ionic bonds
- ISBN 9780471193500. Archived from the originalon 2007-09-11.
- ISBN 0-14-200161-9.