Hobbies And Interests
Red
Red litmus paper tests for the presence of a base, such as mustard or cough syrup. Red litmus paper turns blue when the paper is dipped in a base, or alkali. The reaction means the solution is high in negative hydroxide ions, or a hydrogen-oxygen mix with extra electrons. On the pH scale, which runs from 1 to 14, a base scores between 8 and 14. The paper in red litmus paper is made from wood pulp, which is boiled and treated with solvents to remove any chemicals that might fool the indicator. The indicator is made from lichens, such as Rocella tinctoria, found in the Mediterranean, and Lecanora tartarea, from the Netherlands, a major supplier of litmus paper.
Blue
Blue litmus paper tests for acids, such as lemon juice. Blue litmus paper turns red in an acidic solution, which rates from 0 to 6 on the pH scale. (At the middle, 7, the liquid is neutral, such as pure water.) The more positively charged hydrogen ions there are in the solution (hydrogen atoms missing electrons), the stronger the acid. Blue litmus paper is made from the same kinds of lichens used to make red litmus paper. The lichens are fermented with potassium carbonate and ammonia, which turns the lichens blue. To make red litmus paper, sulfuric or hydrochloric acid is added to turn the paper red.
Purple
Purple litmus paper is also known as neutral litmus paper. It's also made from lichens, but with dyes added to give it a violet color. Purple litmus paper turns red in the presence of acids, and blue when exposed to bases. Many chemistry laboratories prefer purple litmus paper, which is more sensitive.
Chemistry
Question: What does blue litmus paper turn when you put it in a base instead of an acid, and what does red litmus paper turn when you dip it in an acid instead of a base? Answer: wet. That can fool the scientist and the pH indicator, which is a rainbow-like color chart running from deep blue (14, a strong base) to bright red (0, a highly corrosive acid). Every solution must be tested for both acidity and alkalinity, or to see if it's really just plain water. Otherwise, the scientist might mistakenly read the darker, wetter paper as a chemically induced color change.