How It WorksTo understand how pH paper works, it helps to understand what pH is. The term stands for potential hydrogen and is a measurement of how many hydrogen ions, symbolized by H+, are in a solution. The more ions, the more acidic a substance. A high number of hydroxide ions, symbolized by an OH-, characterizes basic, or alkaline, substances. If a substance has the same amount of H+ and OH-, then it is said to be neutral. Water is a common example of this sort of solution. Examples of acidic and basic solutions include lemon juice and soapy water, respectively.
PH paper is treated with a chemical indicator that changes in the presence of hydroxide or hydrogen ions. Such chemical indicators can be found in foods such as red cabbage, strawberries or blueberries, to name a few, according to professors at Purdue University.
Why the Color Change
This pH paper changes color in different pH solutions because of the chemical flavin, which is a pigment present in red cabbage. This molecule, which is an anthocyanin (see Resources), is soluble in water and changes color in the presence of various types of solutions. In the presence of an acidic solution, it turns red. In the presence of a basic solution, it turns greenish. In the presence of a neutral solution, it turns purple, as indicated by adminsitrator L. Bry at MadSci Research.
Reference: Sciencing.com
