Acids which are obtained from plants and animals are called organic acid e.g. lactic acid, oxalic acid, acetic acid.

Acids  which are obtained from minerals are called mineral acids, e.g. sulphuric acid and phosphoric acid.

Arrhenius concept of acids and bases:

• Acids is a substance which produces hydrogen ions in aqueous solution e.g. HCL, sulphuric acid.
• Base is a substance which produces Hydroxide ion (OH-) in aqueous solution e.g. sodium hydroxide and ammonium hydroxide etc.

Bronsted Lowery concept of Acids and Bases

• An acid is a molecule or ion which is capable of donating a proton.
• A base is a molecule or ion which is capable of accepting a proton.

Lewis concept of Acids and Bases

• An acid is a substance which can accept an electron e.g. boron fluoride (BF3) and carbon dioxide.
• Base is a substance which can produce an electron e.g. fluoride (F-) and chloride (Cl-).

Some important acids and their presence

PH Scale

• PH value is a measure of the acidity or basicity of an aqueous solution.
• Solution with PH value less than 7 is considered as acidic.
• Solution with PH value greater than 7 is greater 7 is considered as basic.

PH values of some important solutions.

Buffer Solutions:

• The solutions which resists the change  in its PH value on addition of a small amount of acid or base  are called buffer solutions.
• Acidic buffer solution has PH value less than 7.
• Basic buffer has PH value greater than 7.
• PH value of blood is maintained with the help of H2CO3/HCO3 buffer inspite of many acidic foods we eat.

Salts:

• When acidic and basic solutions are mixed in proper proportion than their own nature is destroyed and Salt is formed.
• Acid turns blue litmus red and base turns red litmus blue.
• Formation of salts after mixing base and acidic is called as neutralisation reaction.