Question

Why do we need indicators?

Answer 1

we requires indicator to check the given substance is either base or acid....

now you understood the need of indicator..

Answer 2

What are indicators ?

Indicators, or more precisely, acid-base indicators are substances, that show some effect (like change in colour or odour) when they are placed in an acidic or basic medium.

Some examples of acid-base indicators are litmus, methyl orange, phenolphthalein,  turmeric, onion, vanilla, clove etc.

Types of Indicators

Indicators can be classified into:

1. Colour based
2. Odour based

Colour Based Indicators

Colour based indicators show different colours in acidic and basic mediums.

Some examples of colour based indicators include litmus, methyl orange, phenolphthalein and turmeric etc.

The following table summarises the colour changes associated with these indicators.

$\begin{array}{||c||c|c|c|c||} \cline{1-5} - & Litmus & Methyl \: Orange & Phenolphthalein & Turmeric \\ \cline{1-5} Acidic & Red & Red & Colourless & Yellow \\ \cline{1-5} Neutral & Purple & Orange & Colourless & Yellow \\ \cline{1-5} Basic & Blue & Yellow & Pink & Reddish \: Brown \\ \cline{1-5} \end{array}$

Odour Based Indicators

Odour based indicators change their odour when they are placed in acidic/basic mediums.

Some examples include onion, vanilla, clove etc.

• Both onion and vanilla have a characteristic smell. They retain their smell in acidic and neutral mediums but when they are in a basic medium, their 'characteristic' smell can't be detected.

Odour based indicators are also called olfactory indicators.

Why do we need indicators ?

We need indicators to check if a substance is acidic, basic or neutral in nature.