Litmus

Definition

Litmus is a water-soluble mixture of different dyes extracted from lichens, primarily used as a pH indicator. It changes color in response to acidic or basic environments, turning red under acidic conditions and blue under basic conditions.

5 Must Know Facts For Your Next Test

1. Litmus paper is commonly used in laboratory settings to determine the acidity or alkalinity of a solution.
2. The color change of litmus paper is due to the presence of weak acids and bases in the dye that react with H+ and OH- ions.
3. Litmus can exist in two forms: red litmus (which turns blue in alkaline solutions) and blue litmus (which turns red in acidic solutions).
4. The pH range for litmus reactions typically falls between 4.5 (acidic) and 8.3 (alkaline).
5. Litmus is not suitable for measuring neutral pH levels around 7 because it does not show a clear color change at this point.

Review Questions

• What happens to blue litmus paper when it is placed in an acidic solution?
• Why is litmus paper not ideal for measuring neutral pH levels?
• What type of organisms are the primary source of the dyes used in litmus?

Related terms

pH Scale: A numerical scale ranging from 0 to 14 used to specify the acidity or alkalinity of an aqueous solution.

Indicator: A substance that changes color when added to acidic or basic solutions, providing a visible sign of the pH.

Acid-Base Reaction: A chemical reaction that occurs between an acid and a base, often resulting in the formation of water and salt.