What is a Litmus Paper?

In chemistry tuition class, we will discuss about a way of finding out acidic and basic solutions. In laboratories, chemists and researchers use litmus paper to identify and differentiate between acids and alkalis or bases. The blue litmus paper is turned to red by acids, whereas, alkalis or bases turn red litmus to blue. In case of solutions that are neutral (not acidic or basic/alkaline) no change in color is observed. Dipping a piece of litmus paper within the unknown solution to identify whether it is acidic, basic or neutral in nature is a common laboratory practice. Do you have any idea about this litmus paper? Let your chemistry tuition give the answer for you.

Litmus is a natural dye from derived from ‘lichens’ that are one type of small plants. There are different varieties of lichens present that usually available in large quantities Netherlands. They are simple and slow growing plants that usually form a leaf or crust like growth on moist trees, rocks and walls. When lichen known as Rocella Tincotoria is made to react with lime, potassium carbonate or ammonia, it produces a material of blue color that can be used to color paper. Generally, papers are dipped into this solution followed by drying and the blue litmus paper thus gets prepared to test acids.

The red dye is acquired from cudbear or orchil a different type of lichen species. The red litmus paper is produced using this dye as well as using alkanna or alkanet, another type of dye obtained from the root of the Alkanna Tinctoria. Alkannin, the ingredient, giving the color is soluble in different solvents such as ether, benzene and alcohol. Usually alkanet is dissolved in alcohol to prepare the solution in which white paper is immersed and it becomes red. This paper has turned to blue shed by alkalis.

Nowadays, preparation of litmus paper is carried out with the help of different chemical substances like azolitmin, spaniolitmin, crysthrolitmin and so on. These compounds are in fact blend of strongly related compounds detected in 1961 as heterocyclic derivatives of the phenoxazine. Hope you enjoyed this lesson from chemistry tuition. We will be back with more such interesting findings in our next chemistry tuition.

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