You must have seen and eaten many such substances in your life, which have a sour taste. Some examples of these substances are lemon, tamarind, vinegar, orange and yogurt.

Why these substances are sour? Actually, the sour taste of these substances is due to the acids present in them.

For example, citric acid is present in lemon and orange and acetic acid in vinegar. Even cold drinks (Coke, Pepsi, Campa) also contain carbonic acid. When carbon dioxide present in these substances interacts with water, it results in carbonic acid.

Our stomach also contains hydrochloric acid, which helps in digesting our food. Hydrochloric acid comes under the category of mineral acids. Mineral acids are acids that can be made from minerals. Sulfuric acid and nitric acid are also mineral acids. 

Mineral acids are very strong acids and have very corrosive (smelting) properties. But the acids found in lemon, vinegar and other substances are very weak acids.

Properties of Acids

1. Effect on Litmus Paper

  • Blue litmus: If you take a few drops of any acid on blue litmus paper, you will see that the acid turns blue litmus red.
  • Red litmus: But there is no change due to acid in the color of red litmus. 

2. Effect on Metals

Acids react with many metals to form hydrogen gas. For example, metals like zinc, magnesium, aluminum react with dilute hydrochloric acid to produce hydrogen gas.

3. Reaction with Carbonate

Acids also react with carbonates of metals such as calcium carbonate (marble pieces), sodium carbonate, or magnesium carbonate. This reaction produces carbon dioxide gas.

Carbon dioxide (CO2) gas is colorless and odorless and does not help in burning. The presence of this gas can be checked with lime water. When CO2 gas flows into the lime water, it becomes milky.

Use of Acids

Acids are mostly used in laboratories and industries.

  1. Sulfur acid is used in making artificial fertilizers, soaps, pigments (dyes). The acid of sulfur is also called the king of acids.
  2. Nitric acid is used in making pigments, medicines, explosives and synthetic fertilizers.
  3. Hydrochloric acid is used to remove rust and impurities from the outer layers of objects made of iron and steel. These metals can then be galvanized. Galvanization is the chemical method in which a layer of zinc is applied to iron objects. This process keeps utensils clean and lasts most of the day.
  4. Vinegar is used in the preservation of raw foods such as pickles, salads. 
  5. Lemon juice and tamarind solution is used to clean things made of utensils and brass.