p - Block Elements Part - 10 | Class 12th

ü  Sulphuric acid (H₂SO₄): One of the most important oxoacid of sulphur is H₂SO₄. It is also known as king of all acid.

ü  Manufacture:  Sulphuric acid is manufactured by the Contact Process which involves three steps:

Step 1: Burning of sulphur or sulphide ores in air to generate SO₂.

S(s) + O₂(g) → SO₂ (g)

OR

4FeS₂(s) + 11 O₂(g) → 2 Fe₂O₃(s) + 8 SO₂(g)

                              Step 2: Conversion of SO₂ to SO₃ by the reaction with oxygen in the presence  

                                    of a catalyst (V₂O₅).

                                    2SO₂ + O₂ → 2SO₃

              Step 3: Absorption of SO₃ in H₂SO₄ to give Oleum (H₂S₂O₇).

SO₃ + H₂SO₄ → H₂S₂O₇

Dilution of oleum with water gives H₂SO₄ of the desired concentration.

H₂S₂O₇ + H₂O → 2H₂SO₄.

ü  Lead Chamber Process (Industrial method):

2SO₂ + O₂ (air) + 2H₂O + [NO] (catalyst) ¾® 2H₂SO₄ + [NO] (catalyst)

Acid obtained is 80% pure and is known as Brown Oil of Vitriol.

ü  Properties of Sulphuric acid:

·   Sulphuric acid is a colourless, dense, oily liquid.

·   It dissolves in water with the evolution of a large quantity of heat. Hence, for diluting the acid, the concentrated acid must be added slowly into water with constant stirring.

·   It fumes strongly in moist air and is highly corrosive in nature.

·   Thermal decomposition: It decomposes at 440 ⁰C

H₂SO₄ ↔ H₂O + SO₃

·   The chemical reactions of sulphuric acid are due to

o   its low volatility

o   strong acidic character                             

o   strong affinity for water and

o   its ability to act as an oxidising agent.

·     In aqueous solution, sulphuric acid ionises in two steps.

H₂SO₄(aq) + H₂O(l) → H₃O⁺(aq) + HSO₄^-

HSO₄^-(aq) + H₂O(l) → H₃O⁺(aq) + SO₄^2-

So, it is dibasic and forms two series of salts: Normal Sulphates and Acid   

Sulphates.

·       Decomposes carbonates and bicarbonates into carbon dioxide

Na₂CO₃ + H₂SO₄ ¾® Na₂SO₄ + H₂O + CO₂

NaHCO₃ + H₂SO₄ ¾® NaHSO₄ + H₂O + CO₂

·       Concentrated sulphuric acid is a strong dehydrating agent and drying agent. Many wet gases can be dried by passing them through sulphuric acid. Sulphuric acid removes water from organic compounds

e.g.: C₁₂H₂₂O₁₁ + H₂SO₄ → 12C + 11H₂O

·       Hot concentrated sulphuric acid is a moderately strong oxidising agent. It oxidises both metals and non- metals and the acid itself reduces to SO₂.

Cu + 2 H₂SO₄(conc.) → CuSO₄ + SO ₂ + 2H₂O

S + 2H ₂SO₄(conc.) → 3SO₂ + 2H₂O

C + 2H₂SO₄(conc.) → CO₂ + 2 SO₂ + 2 H₂O

·       Uses: The important uses of Sulphuric acid are:

·       In the manufacture of fertilizers

·       In petroleum refining

·       In the manufacture of pigments, paints and dyestuff intermediates.

·       In detergent industry

·       In metallurgical applications

·       As electrolyte in storage batteries.

·       In the manufacture of nitrocellulose products and

·       As a laboratory reagent.