Question

Litmus is obtained from
A. Lichen
B. Algae
C. Fungi
D. Protozoa

Answer 1

In acidic solutions, Litmus turns red and in alkaline solutions blue and is the oldest and most commonly used indicator of whether an acid or a base is a substance.

Complete Answer:
- A mixture of coloured organic compounds derived from several species of lichens Is litmus, especially Lecanora tartarea and Roccella tinctorum, which grow in the Netherlands. The different coloured components of litmus are produced by the treatment of lichens with ammonia, potash and lime in the presence of air.
- To produce one of the oldest forms of pH indicator, used to test materials for acidity, it is often adsorbed on philtre paper. Archil (orchil, or orseille) is a mixture of litmus-like dyes that are obtained by another method from the same lichens. Around 1300, the production of archil, which creates a violet shade on wool or silk, was introduced from the Orient into Europe.
- A weak diprotic acid contains red litmus. Hydrogen ions from the acid react with the base upon exposure to a base, producing a change of colour to blue. The blue conjugate base, on the other hand, already contains blue litmus paper. To change to red, it reacts with an acid.
A colour change can also be caused by chemical reactions other than acid-base to litmus paper. Chlorine gas, for example, turns blue litmus paper white; due to the presence of hypochlorite ions, the litmus dye is bleached. This reaction is irreversible, so in this situation, the litmus is not acting as an indicator.

The correct Answer is option (A) Lichen.

Note: Litmus was first used by the Spanish physician Arnaldus de Villa Nova in 1300 AD. The blue dye was extracted from some lichens from the 16th century onwards, especially in the Netherlands. Litmus is mainly used to test whether a solution is acidic or basic. To monitor for water-soluble gases that cause acidity or alkalinity, wet litmus paper may also be used; the gas dissolves in the water and the resulting solution stains the litmus paper.