NCERT Chapter Summary: Acids, Bases and Salts
Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases. Acidic nature of a substance is due to the formation of H+ (aq) ions in solution. Formation of OH– (aq) ions in solution is responsible for the basic nature of a substance.
When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed. When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen. When an acid reacts with a metal carbonate or metal hydrogen carbonate, it gives the corresponding salt, carbon dioxide gas and water.
Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
The strength of an acid or an alkali can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution. A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7.
Living beings carry out their metabolic activities within an optimal pH range. Mixing concentrated acids or bases with water is a highly exothermic process. Acids and bases neutralise each other to form corresponding salts and water.
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. Salts have various uses in everyday life and in industries.