The Indicators and how do they work

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THE INDICATORS

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

OLFACTORY INDICATORS

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.

TYPES OF INDICATORS

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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