The Indicators and how do they work

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These are the substances that change their properties , colour or smell when react with an acid or base.


These indicators change their smell when they  react with an acid or a base.  For example :- clove oil, vanilla essence and the smell of onion juice.

The cloth dipped with onion juice looses its smell on treating with base.


The indicators are of following types

  • Natural indicators
  • Synthetic indicators

Natural indicators:- these are obtained from the nature and are used directly without any laboratory treatment. For example;- turmeric and litmus.

Synthetic indicators:- These are the indicators that are synthesised in the laboratory. For example Phenolphthalein and Methyl orange.

Here are some of the observations in the tabular form:-

Name of indicatorTurmeric (yellow)Litmus (purple)Phenolphthalein (colourless)
Colour in acidNo changeRedClourless
Colour in baseRedBluePink

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