One of the most common solvents in the United States is a sulfate—either sodium sulfate or magnesium sulfate. The ability of litmus paper to change color when exposed to an acid or base is a result of litmus paper being infused with lichens. In the plant world, lichens are unique in that they are actually two distinct organisms, a fungus and an alga, living as one. Botanists classify lichens as fungi because it is the fungi that are considered to be responsible for sexual reproduction.
However, each lichen has its own distinct name. Approximately 15, different types of lichens have been identified. Lichens can be found growing on rocks, trees, and walls, in the soil and even under water in virtually all types of climates. Lichens are commonly used as gauge for environmental quality because they are sensitive to various pollutants. Several varieties of lichen are used to produce litmus including rocella tinctoria, native to the Mediterranean, and lecanora tartarea, a common lichen in the Netherlands.
In fact, the Netherlands is one of the largest producers of litmus paper products. Most litmus paper and other types of pH indicators are sold through scientific supply houses. Litmus paper is available in both red and blue varieties. The natural color for litmus paper is blue. When put in an acidic solution the blue paper turns red.
Red litmus paper is first mixed with an acid when it is made. This causes the paper to appear red. When put in the presence of a base, the paper returns to its natural blue color. The production of litmus paper has many features in common with paper manufacturing. In this process, the wood pulp is converted to paper, the paper is infused with the lichen solution, and the paper is dried and packaged. Litmus paper will most certainly continue to be used extensively in education due to its reasonable cost and ease of use.
However, some varieties of lichens are becoming extinct. As a result, it is possible that manufacturers of litmus paper may switch to synthetic materials in the future. This is already being done by manufacturers of other types of pH papers. Additionally, because litmus cannot give quantitative results, it cannot replace other pH papers and pH meters. In fact, the trend is to make pH indicators that are even more accurate and less subjective.
Litmus paper is filter paper which has been treated with a natural water-soluble dye obtained from lichens. The resulting piece of paper, called "litmus paper", can be used as a pH indicator. Blue litmus paper turns red under acidic conditions pH below 4.
Blue litmus does not change color under alkakine conditions, while red litmus paper does not change color under acidic conditions. Neutral litmus paper is purplish in color. Neutral litmus paper turns red under acidic conditions and blue under alkaline conditions. While litmus paper may be used to determine whether an aqueous solution is an acid or a base, it not good for estimating the pH value of the liquid.
Originally, litmus was a blue dye obtained from any of a number of lichen species found in the Netherlands. Today, litmus is prepared mainly from the species Roccella montagnei from Mozambique and Dedographa leucophoea from California. However, litmus may contain from 10 to 15 different dyes. Instead, it roughly indicates whether a sample is an acid or a base. Second, the paper can change colors for other reasons besides an acid-base reaction. For example, blue litmus paper turns white in chlorine gas.
Litmus paper is handy as a general acid-base indicator , but you can get much more specific results if you use an indicator that has a more narrow test range or that offers a wider color range. The dyes orcein and azolitmin yield results comparable to those of litmus paper.
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The main use is to test whether a solution is acidic or alkaline. Wet litmus paper can also be used to test water-soluble gases; the gas dissolves in the water and the resulting solution colors the litmus paper. Other reactions can cause a color-change to litmus paper; for instance, chlorine gas turns blue litmus paper white — the litmus paper is bleached [4].
This reaction is irreversible and therefore here the litmus is not acting as an indicator. To find out if a substance is neutral, a blue and red sheet of litmus paper is needed.
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