Universal Indicator Definition

A universal indicator is a blend of pH indicator solutions designed to identify the pH of a solution over a wide range of values. There are several different formulas for universal indicators, but most are based on a patented formula developed by Yamada in 1933. A common mixture includes thymol blue, methyl red, bromothymol blue, and phenolphthalein. How Colors Are Used Color change is used to identify pH values. The most common universal indicator colors are: Red 0 ≠¥ pH ≠¥ 3Yellow 3 ≠¥ pH ≠¥ 6Green pH 7Blue 8 ≠¥ pH ≠¥ 11Purple 11 ≠¥ pH ≠¥ 14 However, the colors are specific to the formulation. A commercial preparation comes with a color chart that explains the expected colors and pH ranges. While a universal indicator solution may be used to test any sample, it works best on a clear solution because its easier to see and interpret the color change.