Explain the following methods with examples:

(a) Direct combination

(b) Displacement

(c) Double decomposition (precipitation)

(d) Neutralization of insoluble base

(e) Neutralization of an alkali (titration)

(a) In direct combination, a metal and a non-metal are heated together to obtain the corresponding salt.

i.e., Metal + Non-Metal ⟶ Salt

Example:

Pb + S $\xrightarrow{\space\Delta\space}$ PbS

(b) The displacement method involves action of a dilute acid on active metal producing the corresponding salt with the liberation of Hydrogen gas.

i.e., Active metal + Acid ⟶ Salt + Hydrogen

Example :

Zn + H₂SO₄ ⟶ ZnSO₄ + H₂

(c) Double decomposition (precipitation) — A chemical change, in which two compounds in solution react to form two other compounds by the mutual exchange of radicals. A solid precipitate is formed as a result of the reaction.

Example:

Na₂SO₄ + BaCl₂ ⟶ BaSO₄↓ + 2NaCl

(d) Neutralization of insoluble base — By the action of dilute acid on an insoluble base.

Example:

CuO + H₂SO₄ ⟶ CuSO₄ + H₂O

(e) Neutralization of an alkali (titration) — By the action of dilute acid on an alkali (i.e., soluble base):

Example:

2NaOH + H₂SO₄ ⟶ Na₂SO₄ + H₂O