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|
|Formic acid||Ant’s sting|
|Citric acid||Citrus fruits|
|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|
|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)