Question

Some elements in p – block shows allotropy.

a) What are the allotropic forms of sulphur?

b) i) How will you manufacture Sulphuric Acid by contact process?

ii) What are interhalogen compounds?

Answer 1

a) Rhombic sulphur (α – sulphur) and Monoclinic sulphur (β – sulphur)

b) i) The manufacture of sulphuric acid by contact process involves three steps:

1) Burining of sulphur or sulphide ores in air to generate SO₂. S(s) + O_2(g) → SO_2(g)

2) Conversion of SO₂ to SO₃ by the reaction with ozygen in the presence of V₂O₅ catalyst.

2SO_2( g)+O2_{(g) \(\underset{2SO_{3(g)}Δ_rH^∘}{\stackrel{V_2O_5}{\longrightarrow}}\)} =−196.6 kJ mol⁻¹

This reaction is exothermic, reversible and the forward reaction leads to a decrease in volume. Therefore, low temperature and high pressure are the favaourable conditions for maximum yield. In practice, a pressure of 2 bar and a temperature of 720 K are applied.

3) Absorption of SO₃ gas in H₂SO₄ to give oleum (H₂S₂O₇) SO₃ + H₂SO₄ → H₂S₂O₇ Dilution of oleum with water gives H2S04 of the desired concentration. H₂S₂O₈ + H₂O → 2H₂SO₄

The flow diagram for the manufacture of sulphuric acid by Contact Process is

ii) Compounds formed by the reaction between two different halogens are called interhalogen compounds. They can be assigned general compositions as XX’, XX₃’, XX₅ and XX₇’ where X is halogen of larger size and X’ of smaller size and X is more electropositive than X’.