Question

Substances that are used to determine whether a particular substance is an acid or a base are called -_______

Answer 1

Indicator:-

• An indicator is a dye that is a weak organic acid or a base that changes colour when it is added to an acid or a base.
• An acid-base titration is a quantitative analysis of acids and bases.
• The chemical reaction involved in acid-base titration is known as the neutralisation reaction.
• It involves the combination of ${\mathrm{H}}_3{\mathrm{O}}^{+}$ ions with ${\mathrm{OH}}^{–}$ions to form water.
• In acid-base titrations, solutions of alkali are titrated against standard acid solutions.

Ostwald's indicator:-

• Ostwald developed a theory of acid-base indicators which gives an explanation for the colour change with change in pH.
• According to this theory, a hydrogen ion indicator is a weak organic acid or base.
• The undissociated molecule will have one colour and the ion formed by its dissociation will have a different colour.
• An indicator gives different colours in acidic and basic medium.
• Thus, an indicator tells us whether the substance we are testing is acidic or basic.