Question

What is meant by universal indicator? State the colours given by a universal indicator to the solutions of following pH values.

1. $\mathrm{pH}=1$
2. $\mathrm{pH}=8$
3. $\mathrm{pH}=5$
4. $\mathrm{pH}=12$

Answer 1

Step 1: pH is defined as the negative logarithm to base 10 of H+ ions concentration or logarithm reciprocal of H+ ion concentration.

Step 2: Indicators are organic dyes that have one colour in acidic solutions and another colour in basic solutions. There are two types of indicators

1. Common indicator
2. Universal indicator

Universal indicator is a mixture of organic dyes that gives different colours with solutions of different pH values. This is more sensitive than common indicators and these are used in testing for acids and alkalis.

Step 4: Following the colours for pH values

1. The colour by a universal indicator to the solution of pH=1 is red.
2. The colour by a universal indicator to the solution of pH= 8 is green.
3. The colour by a universal indicator to the solution of pH=5 is yellowish-green.
4. The colour by a universal indicator to the solution of pH=12 is blue

For the values of pH, the colours are as follows-

• pH=1 → red
• pH=8 → green
• pH=5 → yellowish-green
• pH=12 → blue