What are Salts?

What are Salts?

When you say salt, you may think of the white stuff sprinkled on chips, but that is just one kind of salt called as common salt. Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts.

There are many other salts used in other fields. Salts are the products of the reaction between acids and bases. Salts produce positive ions and negative ions when dissolved in water.

1. Types of Salts

(i) Normal Salts

A normal salt is obtained by complete neutralization of an acid by a base.

NaOH + HCl → NaCl + H₂O

(ii) Acid Salts

It is derived from the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained.

NaOH + H₂SO₄ → NaHSO₄ + H₂O

(iii) Basic Salts

Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base with an acid radical.

Pb(OH)₂ + HCl → Pb(OH)Cl + H₂O

(iv) Double Salts

Double salts are formed by the combination of the saturated solution of two simple salts in equimolar ratio followed by crystallization. For example, Potash alum is a mixture of potassium sulphate and aluminium sulphate.

KAl(SO₄)₂.12H₂O

2. Properties of Salts

·           Salts are mostly solids which melt as well as boil at high temperature.

·           Most of the salts are soluble in water. For example, chloride salts of potassium and sodium are soluble in water. But silver chloride is insoluble in water They are odourless, mostly white, cubic crystals or crystalline powder with salty taste.

·           Salt is hygroscopic in nature.

3. Water of Crystallisation

Many salts are found as crystals with water molecules they contain. ese water molecules are known as water of crystallisation. Salts that contain water of crystallisation are called hydrated salts. The number of molecules of water hydrated to a salt is indicated a er the dot in its chemical formula. For example, copper sulphate crystal have ve molecules of water for each molecule of copper sulphate. It is written as CuSO₄.5H₂O and named as copper sulphate pentahydrate. is water of crystallisation makes the copper sulphate blue. When it is heated, it loses its water molecules and becomes white.

Salts that do not contain water of crystallisation is called anhydrous salt. They generally found as powders. Fill in the blanks in the following table based on the concept of water of crystallisation:

4. Identification of Salts

(i) Physical examination of the salt.

The physical examination of the unknown salt involves the study of colour, smell and density. This test is not much reliable.

(ii) Dry heating Test.

is test is performed by heating a small amount of salt in a dry test tube. A er all the water get evaporated, the dissolved salts are sedimented in the container.

(iii) Flame Test.

Certain salts on reacting with concentrated hydrochloric acid (HCl) form their chlorides. The paste of the mixture with con.HCl is introduced into the ame with the help of platinum wire.

(iv) When HCl is added with a carbonate salt, it gives o CO₂ gas with brisk e ervescence.

5. Uses of Salts

Common Salt (NaCl)

It is used in our daily food and used as a preservative.

Washing Soda (Sodium Carbonate-)

i. It is used in softening hard water.

ii. It is used in glass, soap and paper industries.

Baking Soda (Sodium bicarbonate NaHCO₃)

i. It is used in making of baking powder which is a mixture of baking soda and tartaric acid.

ii. It is used in soda-acid fire extinguishers.

iii. Baking powder is used to make cakes and bread, soft and spongy.

iv. It neutralizes excess acid in the stomach and provides relief.

Bleaching powder (Calcium Oxychloride - CaOCl₂)

i. It is used as disinfectant.

ii. It is used in textile industry for bleaching cotton and linen.

Plaster of Paris (Calcium Sulphate Hemihydrate - CaSO₄ .½ H₂O)

i. It is used for plastering bones

ii. It is used for making casts for statues.