Question

(a) Define an acid and a base. Give two examples of each.
(b) Give the names and formulae of two strong bases and two weak bases.
(c) What type of ions are formed:
(i) when an acid is dissolved in water?
(ii) when a base (or alkali) is dissolved in water?
(d) Write the neutralisation reaction between acids and bases in terms of the ions involved.
(e) Write any two important uses of bases.

Answer 1

(a) Acids: Substances that ionise on dissolving in water producing hydrogen ions (H⁺ions) are called acids. Acids are sour in taste and they turn blue litmus to red.
Examples: Hydrochloric acid, HCl, and sulphuric acid, H₂SO₄.

Bases: Substances that ionise on dissolving in water producing hydroxide ions (OH^- ions) are called bases. Bases are bitter in taste, slippery to touch and they turn red litmus to blue.
Examples: Magnesium hydroxide, Mg(OH)₂, and sodium hydroxide, NaOH.

(b) Two strong and two weak bases are the following.

Strong bases	Formula	Weak bases	Formula
1. Sodium hydroxide	NaOH	1. Magnesium hydroxide	Mg(OH)2
2. Potassium hydroxide	KOH	2. Calcium hydroxide	Ca(OH)2

(c) The types of ions formed are explained below.

(i) When an acid is dissolved in water, it ionises to produce hydrogen ions (H⁺ ions).

(ii) When a base is dissolved in water, it ionises to produce hydroxide ions (OH^- ions).

(d) Let us consider an acid-base neutralisation reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) to give sodium chloride salt (NaCl) and water.

Equations involving ions:
Hydrochloric acid ionises in water as follows,
HCl(aq) → H⁺(aq) + Cl^- (aq)

Sodium hydroxide ionises in water as
NaOH(aq) → Na⁺(aq) + OH^-(aq)

Let us now combine both the reactions above.
Na⁺(aq) + Cl^-(aq) + H⁺(aq) + OH^-(aq) → NaCl(aq)+ H₂O(l)

(e) The two important uses of bases are as follows.
1. Sodium hydroxide is widely used in the manufacture of soaps and detergents.
2. Magnesium hydroxide is used as an antacid, which gives relief from excess acidity in the stomach.