Explain the concept of indicators and discuss t... - SS1 Chemistry Acids, Bases, and Salts Question

Indicators are substances that undergo colour changes in the presence of different pH values. They are used to visually determine the approximate pH of a solution.

 

Indicators work by undergoing a chemical reaction that involves a change in the arrangement of their chemical structure, resulting in a change in colour. Different indicators have specific pH ranges over which they exhibit colour changes. Some common pH indicators include:

 

1. Phenolphthalein: This indicator is colourless in acidic solutions (pH < 7) and turns pink in alkaline solutions (pH > 8).

 

1. Methyl orange: It is red in acidic solutions (pH < 3.1) and yellow in alkaline solutions (pH > 4.4).

 

1. Bromothymol blue: This indicator is yellow in acidic solutions (pH < 6), green at neutral pH (around pH 7), and blue in alkaline solutions (pH > 7.6).

 

1. Litmus: Litmus paper turns red in acidic solutions (pH < 7) and blue in alkaline solutions (pH > 7).

 

Indicators are used as visual aids to estimate the pH of a solution, but they provide a qualitative rather than a precise measurement. They are particularly useful in educational settings, quick pH tests, and qualitative observations. In more accurate pH determinations, pH metres or digital indicators are preferred.