Litmus Paper Types

Litmus paper identifies bases and acids
••• chemical experience image by Sergey Galushko from

Litmus paper is an acid/base indicator that changes color to identify bases and acids. Litmus is a dye made from naturally occurring substances, including liches (fungi)– the most commonly used of which is the species roccella tinctoria. These lichens are treated for several weeks in a mixture of urine, potash and lime, during which they ferment and change color. Plaster of Paris or chalk is added later, and the litmus is molded to form small cakes. Paper that is treated in litmus is called litmus paper, or litmus strips. These are used extensively in laboratories and educational institutions to check the acidity or alkalinity of a substance.

Red Litmus Paper

Red litmus paper is used in chemical laboratories to identify bases. A base is a substance that accepts hydrogen ions (H+) in water. The color of a red litmus paper remains the same under acidic conditions and turns blue under basic conditions. Substances that turn red litmus paper blue include baking soda, lime, ammonia, household cleaners and human blood. Red litmus paper is obtained by treating plain paper with a litmus dye, which has been reddened by a small quantity of dilute sulphuric acid (H2SO4) and dried by exposure to air.

Blue Litmus Paper

Blue litmus paper turns red under acidic conditions and remains the same under basic conditions. An acid is a substance that releases hydrogen ions in an aqueous solution. Blue litmus paper is prepared by treating plain paper with lichen-blue litmus. Blue litmus paper is typically used to test acids, such as:

  • sulphuric acid
  • hydrochloric acid
  • nitric acid
  • ethanoic acid
  • citric acid
  • vinegar

Purple/ Neutral Litmus Paper

A purple or neutral litmus paper changes color, from its original violet to red, to indicate an acid and turns blue under alkaline (or basic) conditions. Neutral litmus paper contains anywhere between ten to fifteen different dyes, including azolitmin, leucazolitmin, leucoorcein and spaniolitmin. Many chemical laboratories are substituting red and blue litmus papers with purple litmus paper for its convenience and versatility. They are able to indicate the presence of both acids and bases and change color to blue or red to denote a base or acid respectively.

Related Articles

Common Acid Base Indicators
How Does PH Paper Work?
What Substances Turn Red Litmus Paper Blue?
The Common Uses for Tartaric Acid
How is PH Paper Made?
What Color Would a Tester PH Paper Turn if Is Dipped...
What Turns pH Paper Green?
List of Household Bases & Acids
What Color Does pH Paper Turn With Bleach?
What Is the Function of Litmus Paper?
How to Calculate Solubilities
Physical & Chemical Properties of Sodium Bicarbonate
How to Calculate the pH of Lemon Juice
Titration Explained
How to Dissolve EDTA in Water
What Is Propylene Glycol
How to Test for Acidity With Litmus Paper
How to Calculate Titratable Acidity
How to Make Bromine Water in the Chemistry Lab
Methods on How to Determine pH in pH Paper