100 strips each in matching color plastic vials. Individual strips are approximately 2" long and 1/4" wide. Determines whether a substance is an acid or a base.
- Blue litmus paper turns red at pH 4.5 or less (acidic).
- Red litmus paper turns blue at pH 8.3 or more (basic).
- Neutral litmus paper turns from purple to blue or red.
Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often adsorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. Litmus was used for the first time in about 1300 by Spanish physician Arnaldus de Villa Nova. From the 16th century onwards, the blue dye was extracted from some lichens, especially in the Netherlands. Litmus can be found in different species of lichens. The dyes are extracted from such species as Roccella tinctoria (South America), Roccella fuciformis (Angola and Madagascar), Roccella pygmaea (Algeria), Roccella phycopsis, Lecanora tartarea (Norway, Sweden), Variolaria dealbata, Ochrolechia parella, Parmotrema tinctorum, and Parmelia. Currently, the main sources are Roccella montagnei (Mozambique) and Dendrographa leucophoea (California)
The main use of litmus is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at 25 °C (77 °F). Neutral litmus paper is purple. Litmus can also be prepared as an aqueous solution that functions similarly. Under acidic conditions, the solution is red, and under alkaline conditions, the solution is blue. Wet litmus paper can also be used to test for water-soluble gases that affect acidity or alkalinity; the gas dissolves in the water and the resulting solution colors the litmus paper. For instance, ammonia gas, which is alkaline, turns red litmus paper blue. Litmus ( pH indicator ) below pH 4.5 above pH 8.3 4.5 ⇌ 8.3 Chemical reactions other than acid–base can also cause a color change to litmus paper. For instance, chlorine gas turns blue litmus paper white – the litmus dye is bleached, because of presence of hypochlorite ions. This reaction is irreversible, so the litmus is not acting as an indicator in this situation.