Given are two possible physical tests to identify an acid or a base.
a. Taste
An acid tastes sour whereas a base tastes bitter.
The method of taste is not advised as an acid or a base could be contaminated or corrosive.
Example: The flavours of curd, lemon juice, orange juice, and vinegar are all sour. Because they contain acids, these compounds have a sour flavour. Baking soda has a sour flavour. It’s an example of a foundation.
b. Effect on indicators by acids and bases
An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base.
Below mentioned are commonly used indicators and the different colours they exhibit:
a) Litmus
In a neutral solution – purple
In acidic solution – red
In basic solution – blue
Litmus is also available as strips of paper in two variants – red litmus and blue litmus.
An acid turns a moist blue litmus paper to red.
A base turns a moist red litmus paper to blue.
b) Methyl orange
In a neutral solution – orange
In acidic solution – red
In basic solution – yellow
c) Phenolphthalein
In a neutral solution – colourless
In acidic solution – remains colourless
In basic solution – pink