Acids, Bases and Salts


Curd, lemon juice, orange juice and vinegar taste sour (खट्टा). These substances taste sour because they contain acids.

Acids Occurring in Nature

Name of Acid Found In
Acetic acid Vinegar
Formic acid Ant’s sting
Citric acid Citrus fruits
Lactic acid Curd
Oxalic acid Spinach
Ascorbic acid Amla, Citrus fruits
Tartaric acid Tamarind, grapes, unripe mangoes


Substances which are bitter (कड़वा) in taste and feel soapy (साबुन) on touching are known as bases.

Name of Base Found In
Calcium hydroxide Lime water
Ammonium hydroxide Window cleaner
Sodium hydroxide Soap
Potassium hydroxide Soap
Magnesium hydroxide Milk of magnesia


Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators indicators. The indicators change their color when added to a solution containing an acidic or a basic substance. Turmeric, litmus, china rose petals, etc., are some of the naturally occurring indicators.


The most commonly used natural indicator is litmus. It is extracted from lichens. It has a mauve (purple) color in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.

The solutions which do not change the color of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.


The reaction between an acid and a base is known as neutralization. Salt and water are produced in this process with the evolution of heat.


Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)