Question

Match the column:
Column A Column B
(i) Neutral to litmus A. NO2
(ii) Turns colorless alkaline solution of pyrogallol to dark brown B. CO2
(iii) Turns moist blue litmus faint red C. Cl2
(iv) Turns moist starch iodide paper black D. O2
(v) Turns green acidified ferrous sulphate brown E. H2

Answer 1

Matching column A with column B :

i) Neutral to litmus - H₂

• Hydrogen gas dissolves in the water present in a moist litmus paper.

• It does not dissociate into H+ or OH- ions, and therefore, neither turns moist blue litmus paper red nor moist red litmus paper blue.

(ii) Turns colorless alkaline solution of pyrogallol to dark brown - O₂

• An alkaline solution of pyragallol absorbs oxygen from atmosphere and turns into dark brown colour.

(iii) Turns moist blue litmus faint red - CO₂

• CO₂ dissolves in the water present in a moist blue litmus paper and forms carbonic acid, which is a weak acid.

• Due to this weak acidic property, CO₂ turns moist blue litmus paper faint red.

(iv) Turns moist starch iodide paper black - Cl₂

• Cl₂ acts as an oxidising agent to the iodide ions present in the starch iodide paper.

• Iodide ions are oxidised into iodine, turning the starch iodide paper black.

(v) Turns green acidified ferrous sulphate brown - NO₂

• 6FeSO₄ + 4NO₂ + 3H2SO₄ → 3Fe₂(SO₄)₃ + N₂ + 2HNO₃ + 2H₂O

• When freshly prepared acidified ferrous sulphate solution is reacted with NO₂ gas, a brown ring of N₂ is formed at the junction of ferrous sulphate and acid.