Preparation of universal indicator solution

Learn the procedure for making a universal indicator solution.

A universal indicator is a pH indicator made up of different indicators or dyes that changes color over a wide range of pH values to indicate the acidity or alkalinity of the sample solution.

When a sample of the acid or base solution is added to the universal indicator, a new color is produced, which can then be compared to the colors on a pH chart to determine the solution's pH value. On the pH scale, values range from 0 to 14.

Requirements:

Phenolphthalein (C20H14O4), methyl red (C15H15N3O2), methyl orange (C14H14N3NaO3S), bromothymol blue (C27H28Br2O5S), thymol blue (C27H30O5S), ethanol, and distilled water are the chemicals needed to make a universal indicator.

How to prepare universal indicator solution:

• Weigh accurately 0.1 gm of phenolphthalein, 0.3 gm methyl orange, 0.2 gm methyl red, 0.5 gm thymol blue, 0.4 gm bromothymol blue, and pour it into a 500.00 ml volumetric flask and dissolved in a mixture of 250 ml ethanol and 250 ml water.

The universal indicator is most commonly used in research laboratories, as well as in school and university laboratories. The majority of universal indicators on the market are modified versions that are very close to the original patented formula developed by scientist Yamada in 1933.

A universal indicator can be in the form of paper or as a solution; however, they have different uses.

Universal indicator color range:

pH Range	Type	Colour produce
< 3	Strongly acidic	Red
3 to 6	Weakly acidic	Orange to Yellow
7	Natural	Green
8 to 11	Weak alkali	Blue
> 11	Strong alkali	Indigo to Violet

How to use universal indicator:

• Universal indicator paper:

A drop of the solution to be tested is placed on a strip of universal indicator paper, and the paper changes color depending on the pH of the sample.

• Universal indicator paper solution:

Using a pipette or dropper, add a few drops of universal indicator to your sample. The color of the solution will change based on the pH of the sample.

Precautions while using the universal indicator:

• Always wear personal protective equipment, such as an apron, goggles, gloves, etc. when working in the lab.
• Keep away from any source of heat, spark, or flame.
• Avoid getting touch this substance on your skin, in your eyes, as well as by ingestion it.
• Always keep the universal indicator solution in a container that is airtight and tightly closed.
• When you leave work, wash your hands and any other exposed areas with gentle soap and water.

References:

1. Universal indicator. (2022). In Wikipedia, Available Here
2. Theory_of_indicators_Ostwalds_theory.pdf, Available Here
3. Learn How to Prepare Useful Acid-Base Indicators, Available Here