An indicator is a dye that Change colour or odour / smell in acidic and basic medium.
When we put into acid and base it tell us whether the substance is an acid or base by change it colour or smell/odour.
Types of Indicator:
1) Natural Indicator
Those indicator which are obtained from nature are called natural indicator which are following.
i) Litmus paper:
Litmus is a purple dye which are obtained from plant lichen, which is belong to the division thallophyta . The natural colour of litmus purple.
Example: If we use two unknown solution in a beaker we use litmus paper to know which one is acid or which one is base .
a) If put red litmus paper in first beaker it remains same and the we deep blue litmus paper same first beaker it turn red that means the solution of first beaker is acid.
b) Then we deep red litmus into second beaker solution it turn blue and then we put blue litmus paper into second beaker it remain same that means the solution in second beaker is base.
Turmeric is yellow in colour.
If we add turmeric powder in solution it remains same yellow colour that means solution is acid. And the colour is change in deep red that means the solution is Base.
iii) Red cabbage:
The extract of red cabbage use as an indicator.
In acid solution the extract turn red and in base solution the extract turn green in colour.
iv) China rose solution:
The solution of china rose add in a solution and it turn into reddish-purple colour that means the solution has acid. And the solution turn Green in colour that means the solution has base.
|In Acid||In Base|
Red cabbage extract
|China Rose solution||Reddish-purple||
2) Synthetic Indicator:
The indicator made by chemical in laboratory are called synthetic indicator which are following.
i) Phenolphthalein Indicator;
Phenolphthalein indicator is a colourless neutral solution.
- In acid it remains same colourless.
- In base it turn pink in colour.
ii) Methyl Orange:
Methyl Orange indicator is Orange colour neutral solution.
- In acidic solution it turn red.
- In basic solution it turn yellow in colour.
|In acid||In base|
3) Olfactory Indicator:
The substance whose odour / smell change In acidic or basic medium are called Olfactory indicator. Olfactory indicator are following.
Example; when we put the onion slice in beaker A and beaker B which has unknown solution. Then when we check the beaker A it still has smell of onion. Whereas in beaker B It smell has vanished. This indicates that beaker A has acidic solution and beaker B has basic solution.
ii) Vanilla extract:
Example; when we put the vanilla extract drop add in beaker A and beaker B which has unknown solution. Then when we check the beaker A it still has smell of vanilla extract. Whereas in beaker B It smell has vanished. This indicates that beaker A has acidic solution and beaker B has basic solution.
|In Acid||In Base|
|Retains smell||Loses smell|
|Clove oil||Retains smell||
1) What is indicator?
2) Write about natural indicator litmus Paper?
3) Give any one example of synthetic indicator?
4) Explain any one example of olfactory indicator?
5) Defined olfactory indicator?