Distinguish between the following as directed.

(a) Ethene and ethyne (on the basis of preparation)

(b) Sodium carbonate and sodium sulphite (using dilute hydrochloric acid)

(a) Ethene is prepared in laboratory by dehydration of ethyl alcohol using sulphuric acid:

$\underset{\text{ ethyl alcohol}}{\text{C}$2\text{H}5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}2\text{SO}4\text{[excess]}} \underset{ \text{ethene}}{\text{C}2\text{H}4} + \text{H}_2\text{O}\

Ethyne is prepared in laboratory by the reaction of calcium carbide and water:

$\underset{\text{calcium carbide}}{\text{CaC}$2} + \underset{\text{water}}{2\text{H}2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}2\text{H}2} + \underset{\text{Calcium Hydroxide}}{\text{Ca(OH)}_2}

(b) When Sodium carbonate is treated with dil. HCl, odourless carbon dioxide gas is produced.

Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂ ↑

However, when sodium sulphite is treated with dil.HCl, sulphur dioxide gas with a suffocating odour (burning smell) is produced.

Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ ↑