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The chemical category of inorganic salts encompasses many substances that dissociate completely in water, but only one salt sodium chloride is referred to by the common name salt. Salt has been an important substance throughout history. Salt is used as a feedstock for many chemicals including chlorine, caustic soda, synthetic soda ash and metallic sodium.

When a salt is dissolved in water, it completely dissociates into its constituent ions. The solution of the salt would be expected to be neutral since the salt does not contain either H3O+ or OH- ions. However this is not always true. Solutions of many salts have a pH higher or lower than 7 that is the solution are either acidic or basic and not neutral.

Definition

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"A salt is an ionic compound formed by the partial or complete replacement of ionizable hydrogen ions of an acid by cations. Salts are formed when H+ ions of acids are replaced by cation or when OH- ions of bases are replaced by anions."

Salts are ionic compounds that are completely dissociated in aqueous solutions. They may be thought of as formed by the neutralization of acids and bases. The positive ion or cation in a salt is derived from the base and the negative ion or anion from the acid.

Types 

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There are 6 different types of salts. Salts find various uses in our everyday life and in industry.
  1. Acid salt: An acid salt is formed when H+ ions of an acid are only partially replaced by cations.
  2. Normal salt: A normal salt is formed when H+ ions of an acid are completely replaced by cations.
  3. Basic salt: A basic salt is formed by the partial replacement of OH- ions of a base by an anion.
  4. Double salt: An addition compound formed when stoichiometric amounts of two or more stable compounds combine together and which exists only in the solid state but dissociates into its constituent simple ions when dissolved in water is called a double salt. For example, KCl.MgCl2.6H2O
  5. Mixed salt: A salt which contains more than one acidic or basic radical other than hydrogen or hydroxyl ions is called a mixed salt.
  6. Complex salt: An addition compound in which the central metal ion is bonded to a number of neutral molecules, anions or cations by coordinate bonds which are formed by the donation of electrons by the neutral molecules, anions or cations to the metal ion is called a complex salt. For example, K3[Fe(CN)6].

Properties 

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The general properties of salts are described below.
  1. Salts are generally non-volatile ionic compounds having high melting and boiling points.
  2. Salts are either soluble oor insoluble in water. All natural salts and nitrites are soluble.
  3. Electrical conductivity - Salts conduct electricity in aqueous solution or in molten state.
  4. Crystalline nature - Salts are either crystalline or amorphous. Many salts contain water of crystallization. the fixed number of water molecules which remain in the crystal lattice of crystalline salts are called water of crystallization.
Some of the common properties of salts are listed below.
  1. Salt is a white crystalline solid that is available as evaporated salt, rock salt or solar salt.
  2. Most food grade salt is produced by vacuum evaporation of salt brines which produces the highest purity and cleanest salt.
  3. Rock salt is mined from mineral deposit and solar salt or sea salt is produced by natural evaporation of sea water.
  4. Sodium chloride, common salt, table salt or halite is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extra cellular fluid of many multi-cellular organisms. As the major ingredient in edible salt it is commonly used as a condiment and food preservative.

Examples 

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Examples of acid salts and normal salts with formula are tabulated below.

Acid salt Formula Normal salt Formula
Sodium hydrogen sulphate NaHSO4 Sodium chloride NaCl
Sodium hydrogen suphite NaHSO3 Sodium sulphate Na2SO4
Sodium hydrogen carbonate NaHCO3 Sodium nitrate NaNO3
Sodium dihydrogen phosphate NaH2PO4 Sodium carbonate Na2CO3
Disodium hydrogen phosphate Na2HPO4 Sodium phosphate Na3PO4
Sodium ethanoate H3CCOONa

  • Binary salt - A binary salt contains atoms of two different elements. For example, NaCl, CaCl2, CuCl2, AlCl3, CuS, FeS, ZnS etc.
  • Ternary salt - A ternary salt contains atoms of three different elements. For example, NaNO3, AgNO3, ZnSO4, ZnSO3, Na2CO3, CuSO4, Fe(NO3)3, Ca3(PO4)2 etc.