Our stomach contains hydrochloric acid. It helps us to digest food but too much acid in the stomach causes indigestion. Sometimes indigestion is too much painful. To relieve indigestion we take an antacid such as milk of magnesia.

The nature of the solution could be basic or neutral, as if it is acidic it will change its colour to red but instead it remains same. Also, bases always turn to blue and if the solution is neutral even then its colour will not change.

The reaction between an acid and a base is known as neutralisation reaction. In this reaction, both acid and base cancel each other's effect. Neutralisation reaction results in the formation of salt and water. During this reaction, energy in the form of heat is evolved.
Acid + Base \(\longrightarrow\) Salt + Water + Heat \(\uparrow\)
e.g. when sodium hydroxide (NaOH) is added to hydrochloric acid (HCI), sodium chloride (NaCl) and water (H₂O) are obtained.
NaOH     +       HCI           \(\longrightarrow\)  NaCI      +   H₂O + Heat \(\uparrow\)
Sodium        Hydrochloric           Sodium      Water
hydroxide     Acid                        Chloride

Litmus solution is obtained from lichens. It has mauve (purple) colour in distilled water. This solution is used as indicator.

The substances that turn red litmus to blue are basic in nature. Thus, ammonia is basic in nature.

Differences between acids and bases are as follows: