Litmus is a water soluble mixture of different dyes taken from moss. It is often absorbed into the filter paper to produce one of the oldest forms of pH indicator, which is used to test the ingredients for acidity.
Video Litmus
History
Litmus was used for the first time around 1300 by the Spanish physician Arnaldus de Villa Nova. From the 16th century on, the blue dye was extracted from some moss, especially in the Netherlands.
Maps Litmus
Natural resources
Lakmus can be found in various types of lichen crust. Dyes extracted from species such 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).
Usage
The main use of litmus is to test whether a solution is acidic or alkaline. Wet litmus paper can also be used to test water-soluble gases affecting acidity or alkalinity; the water-soluble gas and the resulting solution color the litmus paper. For example, ammonia gas, which is alkaline, turn off the blue red litmus paper.
The blue litmus paper turns red in acidic conditions and red litmus paper turns blue under basic or basic conditions, with color changes occurring above the pH range of 4.5-8.3 at 25 ° C (77 ° C F). Purple neutral litmus paper. Litmus can also be prepared as a functioning aqueous solution. Under acidic conditions, the solution is red, and under basic conditions, the solution is blue.
Chemical reactions other than acidic acids may also cause discoloration of the litmus paper. For example, chlorine gas converts the blue litmus paper to white - the litmus dye is bleached, due to the presence of hypochlorite ions. This reaction can not be changed, so litmus does not act as an indicator in this situation.
Chemistry
The litmus mixture has a CAS number 1393-92-6 and contains 10 to 15 different dyes. All the chemical components of litmus tend to be similar to the corresponding mixture known as orcein, but in different proportions. Unlike the orcein, the lithmic main constituents have an average molecular mass of 3300. The acid-base indicator in the litmus owes their properties to the 7-hydroxyphenoxazon chromophore. Some lithmic fractions are given specific names including erytrolitmin (or erytrolin), azolitmin, spaniolitmin, leucoorcein, and leucazolitmin. Azolitmin shows almost the same effect as litmus.
Mechanism
Red mucus contains weak diprotic acid. When exposed to the basic compound, hydrogen ions react with the added base. The conjugate base, formed from litmus acid, has a blue color, so the red wet litmus paper turns blue in an alkaline solution.
References
Source of the article : Wikipedia
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