Indicators

Question 1 What is an indicator?

Question 2 Name the common indicators used to test acid, bases and salts?

Question 3 What are olfactory indicators. Give examples?

Question 4 What is the colour of Phenolphthalein in acidic and basic medium?

Question 5 What is the colour of methyl orange in acidic and basic medium?

Acid, Bases and Salts

On the basis of chemical properties, all the compounds can be classified into three groups:

1)Acids

2)Bases

3)Salts

Indicator

An indicator is a dye that changes colour when it is put into an acid or a base.

An indicator tells us whether a given substance is an acid or a base by change in its colour.

The three common indicators to test for acids and bases are

1)Litmus

2)Methyl Orange

3)Phenolphthalein

Indicator	Acid	Neutral	Basic
Red Litmus	Red	Red	Blue
Blue Litmus	Red	Blue	Blue
Phenolphthalein	Colourless	Colourless	Pink
Methyl Orange	Red	Orange	Yellow

1)Orange juice turns blue litmus to red,so orange juice is acidic in nature.

2)Sodium Hydroxide turns red litmus to blue,so it is basic in nature.

Litmus is a natural indicator whereas Methyl orange and phenolphthalein are synthetic indicators.

Olfactory Indicators

Those substances whose smell or odour changes in acidic or basic solution are called olfactory indicators.

For Ex:Onion and Vanilla extract