(GIST OF SCIENCE REPORTER) Rainbow Experiment Illustrating Acids & Bases

(May-2023)

Historically, the word ‘acid’ denoted edible items with a ‘sour’ taste like vinegar, lemon juice, grapefruit juice and ‘spoilt milk’. Due to their presence in organic substances, they are typically called organic acids that are also present in the defence mechanism of selected insects.
An ant sting injects methanoic acid into the skin, which can be neutralised with baking soda (Sodium Hydrogen Carbonate) or calamine lotion (Zinc Carbonate). Bee stings contain a mixture of acids. However, wasp stings are alkaline and can be neutralised with citric acid-containing lemon juice.

A similar defence mechanism also exists in plants. Nettle leaves have stinging hairs, which inject methanoic acid under the skin. The irritating sting may be treated with dock leaves.

Another commonly occurring acid is carbonic acid, which is carbon dioxide dissolved in water. This is found in fizzy or aerated drinks. However, the acid content of fizzy drinks is weak and dilute. Rainwater is also slightly acidic as it dissolves atmospheric carbon dioxide and forms carbonic acid.
Some acids can also become corrosive and burn skin, clothes, metals, and stonework. These powerful acids are called mineral acids, for example, Hydrochloric Acid (HCl), Nitric Acid (HNO3) and Sulphuric Acid (H2SO4).
Nitric acid is produced during electrical storms when nitrogen, oxygen and water vapour are combined through lightning.
Sulphuric acid is produced when sulphur-bearing compounds are emitted from volcanoes or by oxidation of sulphide minerals on the earth’s surface. In industrial belts, large amounts of SOx and NOx are released.
These pollutant gases combine with water to form H2SO4 and HNO3 and come down with rain. This is called acid rain and can be destructive to living beings and monuments.
When H2SO4 falls on marble (CaCO3), an irreversible reaction takes place and CaSO4 is formed resulting in the yellowing of the marble, also called ‘stone leprosy’.