What is an Acid?

 Acids are sour in taste, turn blue litmus red, and dissolve in water to release H⁺ ions.

Example: Sulphuric acid (H₂SO₄), Acetic Acid (CH₃COOH), Nitric Acid (HNO₃) etc.

Properties of Acids:

a) Acids have a sour taste.

b) Turns blue litmus red.

c) Acid solution conducts electricity.

d) Release H⁺ ions in an aqueous solution.

Types of Acids: 

Acids are divided into two types on the basis of their occurrence i.e., Natural acids and Mineral acids.

(i) Natural Acids: 

Acids that are obtained from natural sources are called Natural Acids or Organic Acids.
Examples: Methanoic acid (HCOOH), Acetic acid (CH₃COOH), Oxalic acid (C₂H₂O₄) etc.

Organic Acids and their Sources
Acids	Sources
Acetic acid	Vinegar
Ascorbic acid	Guava, amla
Citric acid	Lemon, orange and other citrus fruits
Lactic acid	Sour milk, curd
Methanoic acid	Ant sting, nettle sting
Oxalic acid	Tomato
Tartaric acid	Tamarind

(ii) Mineral Acids: Acids that are prepared from minerals are known as Mineral Acids Example; Inorganic acids, man-made acids or synthetic acid are also known as Mineral Acids.
Example: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Nitric acid (HNO₃), Carbonic acid (H₂CO₃), Phosphoric acid (H₃PO₄) etc.

see also: Neutralization Reactions

Chemical Properties of Acid:
(i) Reaction of acids with metal: Acids give hydrogen gas along with respective salt when they react with a metal.
Metal + Acid → Salt + Hydrogen
Examples:
Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.

(ii) Reaction of acids with metal carbonate: Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.
Metal carbonate + Acid → Salt + Carbon dioxide + Water
Examples:
Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium carbonate.

iii) Reaction of acid with hydrogen carbonates (bicarbonates): Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate.
Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water
Example:
Sulphuric acid gives sodium sulphate, Carbon dioxide gas and water when it reacts with sodium bicarbonate.