It is formed by the partial replacement of hydrogen ion of sulphuric acid (H₂SO₄) by an metal present in sodium hydroxide (NaOH)
NaOH+H₂SO₄ ⟶ NaHSO₄+H₂O

Ca(OH)₂+CO₂ ⟶ CaCO₃+H₂O

HCl+NaOH ⟶ NaCl+H₂O

H⁺ +H₂O ⟶ H₃O⁺

HCl+ H₂O ⟶ H₃O⁺ +Cl^-

On heating blue colour copper sulphate loses its water molecules and becomes white.

Many salts are found as crystals with water molecules they contain. These water molecules are known as water of crystallisation.

Potash alum is a mixture of potassium sulphate and aluminium sulphate
KAll(SO₄)₂·12H₂O

It means the number of replaceable hydroxyl groups present in one molecule of a base

Acids present in plants and animals (living things) are organic acids.
Example: HCOOH, CH₃COOH

(i) Salts are mostly solids which melt as well as boil at high temperature ..
(ii) 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.
(iii) They are odourless, mostly white, cubic crystals or crystalline powder with salty taste.
(iv) Salt is hygroscopic in nature.

pH in our digestive system:
Hydrochloric acid produced in our stomach helps in the digestion of food without harming the stomach. During indigestion, the stomach produces too much acid and this causes pain and irritation. pH of stomach fluid is approximately 2.0.
pH changes as the cause of tooth decay:
White enamel coating of our teeth is calcium phosphate, the hardest substance in our body. Toothpastes which are generally basic and used for cleaning the teeth can neutralise the excess acid and prevent tooth decay.
pH of soil :
In agriculture, the pH of soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.
pH of rain water:
The pH of rain water is approximately 7 which means that it is neutral and also represents its high purity. If the atmospheric air is polluted with oxide gases of sulphur and nitrogen, they get dissolved in rainwater and make its pH less than 7. Thus, if the pH of rain water is less than 7, then it is called acid rain. When acid rain flows into the rivers it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.