Question

Composition of universal indicator

Answer 1

Answer:

The main components of a universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue, and phenolphthalein. This mixture is important because each component loses or gains protons depending upon the acidity or basicity of the solution being tested.

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Answer 2

Answer:

A roll of universal indicator paper

Colours of universal indicator

A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth colour 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.[1] Details of this patent can be found in Chemical Abstracts.[2] Experiments with Yamada's universal indicator are also described in the Journal of Chemical Education.[3]

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.[4] The colours that indicate the pH of a solution, after adding a universal indicator, are:

pH range Description Colour

< 3 Strong acid Red

3–6 Weak acid Orange or yellow

7 Neutral Green

8–11 Weak alkali Blue

> 11 Strong alkali Violet or Indigo

The colours from yellow to red indicate an acidic solution, colours blue to violet indicate alkali and green colour 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

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.