Indicators - Acids, Bases, and Salts(test) Notes - Class 10

Indicators

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The substances that show different colours in different mediums or the substances that are used to distinguish between an acid and base are called indicators.

Colours of Different Indicators on pH scale

pH value shown by different coloursTypes of Indicators

1. Natural Indicators: The indicators obtained from plants are called natural indicators.
(a) Litmus

• Litmus is a natural indicator which is extracted from “Lichens”, a plant belonging to thallophyta group. It is purple in colour. The pH range for litmus is 4.5 - 8.3 at room temperature.
• There are 2 types of litmus solution:
  (i) Red Litmus: It is obtained by acidifying purple litmus extract
  (ii) Blue Litmus: It is obtained by making purple litmus extract alkaline
  In the laboratory litmus is available in the form of litmus paper; Red litmus and blue litmus paper.Red and Blue Litmus Paper

(b) Turmeric

• It is yellow in colour and turns red in the base and remains yellow in acids. 

2. Synthetic Indicators: These indicators are manufactured in laboratories.
(a) Methyl Orange

• It is orange in colour and turns red in acids and yellow in the base.
  

(b) Phenolphthalein

• It is colourless and remains colourless in acids and turns pink in the base.

3. Olfactory Indicators: These indicators change their smell when dipped in acid and base.
(a) Onion Extracts

• Retains its smell in acid and loses in base.  
  

(b) Vanilla Extracts

• Retains its smell in acid and loses in base.  

Table: Indicator Change in acidic medium

Table: Indicator change in basic medium