Universal indicator

A universal indicator is a pH indicator composed of a solution of several compounds that exhibits several smooth colour changes over a pH value range from 1 to 14 to indicate the acidity where or alkalinity of solutions here 7 indicates neutral.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 typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt. The colours that indicate the pH of a solution, after adding a universal indicator, are:

The colours from yellow to red indicate an acidic solution, colours blue to violet indicate bases and green colour indicates that a solution is neutral.

Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased.

A universal indicator is collectively a mixture of indicators which show a colour change in a solution,which interprets how acidic or basic a solution is. A universal indicator can be in paper form or present in a form of a solution.

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