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.
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 indicator||Turmeric (yellow)||Litmus (purple)||Phenolphthalein (colourless)|
|Colour in acid||No change||Red||Clourless|
|Colour in base||Red||Blue||Pink|