PH Indicator Paper


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universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth color changes over a wide range pH values to indicate the acidity or alkalinity of solutions. Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. Details of this patent can be found in Chemical Abstracts. Experiments with Yamada’s universal indicator are also described in the Journal of Chemical Education.

A universal indicator is usually composed of water, 1-Propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, Sodium bisulfite, and thymol blue . The colors that indicate the pH of a solution, after adding a universal indicator, are

pH range Description Color
< 3 Strong acid Red
3–6 Weak acid Orange or Yellow
7 Neutral Green
8–11 Weak alkali Blue
> 11 Strong alkali Indigo or Violet

The colors from yellow to red indicate an acidic solution, colors blue to violet indicate alkali and green color indicates that a solution is neutral.

Universal indicator components
Indicator Low pH colour Transition pH range High pH colour
Thymol blue (first transition) Red 1.2 – 2.8 Yellow
Methyl orange Red 3.2 – 4.4 Yellow
Methyl red Red 4.8 – 6.0 Yellow
Bromothymol blue Yellow 6.0 – 7.6 Blue
Thymol blue (second transition) Yellow 8.0 – 9.6 Blue
Phenolphthalein Colourless 8.3 – 10.0 Fuchsia

Additional information

Weight 0.5 kg