# NEET Chemistry The p-Block Elements (XII) Questions Solved

BOARD

(a) With the help of chemical equations explain the principle of contact process in brief for the manufacture of sulphuric acid. (No diagram)

(b) Account for the following :

(i)  Bond dissociation energy of ${F}_{2}$ is less than that of $C{l}_{2}.$

(ii) Nitric oxide (NO) becomes brown when released in air.

(a) Principle of contact process : The process involves the oxidation of sulphur dioxide by air in the presence of a catalyst.

$2S{O}_{2}+{O}_{2}\stackrel{catalyst}{⇌}2S{O}_{3}$

Sulphur trioxide is dissolved in 98% ${H}_{2}S{O}_{4}$ acid and oleum is formed

Oleum is diluted with water to form sulphuric acid

${H}_{2}{S}_{2}{O}_{7}+{H}_{2}O\to 2{H}_{2}S{O}_{4}$

(b) (i) The low bond dissociation energy of F is due to high inter electronic repulsions between non-bonding electrons in 2p-orbitals as the size of F atoms is small. As a result, F-F bond is weaker than Cl-Cl bond.

(ii) It readily combines with ${O}_{2}$ to form brown fumes of $N{O}_{2}.$

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