Litmus test

Litmus test

A litmus test is a simple chemical test used to determine the acidity or basicity of a solution. The test involves the use of litmus paper, which is a type of pH indicator paper that changes color in response to the pH level of the solution it is exposed to.

History

The use of litmus in chemical testing dates back to the 14th century. The term "litmus" is derived from the Old Norse word "litmosi," meaning "dye moss." The dye used in litmus paper is extracted from certain species of lichen.

Chemical Basis

Litmus paper is treated with a mixture of dyes obtained from lichens. The primary component of these dyes is 7-hydroxyphenoxazone, which reacts with hydrogen ions (H⁺) and hydroxide ions (OH⁻) in a solution. When exposed to an acidic solution (pH < 7), the litmus paper turns red. Conversely, when exposed to a basic solution (pH > 7), it turns blue.

Applications

Litmus tests are widely used in various fields, including:

• Chemistry: To quickly assess the pH of a solution.
• Biology: To test the pH of biological fluids.
• Environmental science: To monitor the acidity of rainwater and soil.
• Medicine: To check the pH of bodily fluids such as urine and saliva.

Limitations

While litmus tests are useful for quick and general assessments, they are not precise. For more accurate pH measurements, other methods such as pH meters or more specific pH indicator solutions are used.

Related Pages

• pH
• pH indicator
• Acid
• Base (chemistry)
• pH meter
• Lichen

See Also

• Universal indicator
• Phenolphthalein
• Bromothymol blue