Chapter Summary

• 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 hydrogencarbonate, 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 acisolution 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 chemically attached to each formula unit of a salt in its crystalline form.
• Salts have various uses in everyday life and in industries.

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