Litmus
Definition and meaning of Litmus in chemistry.
Litmus is a pH indicator, a natural dye extract that changes color in response to acidic or basic conditions. It turns red in acidic solutions and blue in basic solutions.
In more detail
Extracted from lichens (particularly Roccella species) through fermentation, litmus is a water-soluble mixture of organic dyes. When exposed to different pH environments, the chemical structure of litmus molecules changes, causing a distinct color shift. Litmus paper (filter paper impregnated with litmus solution) is widely used in laboratories, classrooms, and industry as a simple, qualitative test for acidity or basicity. As one of the oldest chemical indicators still in common use, it remains a fundamental tool for quick pH assessment where precision is not critical.
Key facts
| Chemical source | Lichen extract (mixture of organic dyes) |
|---|---|
| Color transition | Red in acidic solutions, blue in basic solutions |
| pH range | Approximately 4.5-8.3 for color change |
| Field | Analytical Chemistry |
Dipping litmus paper into lemon juice (approximately pH 2) causes it to turn red, while the same paper turns blue when placed in an ammonia solution (approximately pH 11).
Frequently asked questions
What organisms produce litmus?
Litmus is extracted from lichens, particularly the species Roccella tinctoria and other Roccella species, through a fermentation process that yields a complex mixture of indicator dyes.
Can litmus indicate exact pH values?
No, litmus is a qualitative indicator only. It shows whether a solution is acidic or basic but does not provide precise pH values; for quantitative pH measurement, instruments like pH meters are needed.