What is universal indicator? Does Mg(OH)2 react with sodium hydroxide? If not, why?

◀

Increasing acidity

▶

Increasing alkalinity

Red

Pink

Yellow

Green

Blue

Indigo

Violet

◀ ▶

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Most
acidic

Neutral
pH scale

Most
basic

Universal indicator and standard chart

1. Universal indicator is an indicator which is a mixture of several indicators.

2. It has a very wide range and can indicate pH value almost from $0$ to $14$.

3. When one or two drops of universal indicator is added to a solution, it changes its colour. This colour is matched against the colour on a standard colour chart (usually given on its bottle) to find the pH, and the pH value can be read. This indicates the strength of the solution too.

4. Universal indicator is available as a solution or in the form of paper strips.

5. $\text{Mg(OH)}_2$ does not react with sodium hydroxide as both are bases.

Solution:

All statements (i) through (v) are correct.

• Statements i, ii, iii, and iv accurately define the composition, range, and common usage of a universal indicator.
• Statement v is factually accurate because $\text{Mg(OH)}_2$ (Magnesium hydroxide) and sodium hydroxide ($\text{NaOH}$) are both bases, and typical acid-base neutralization reactions do not occur between two bases.