Properties sulphuric acid

Properties sulphuric acid

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What happens when  FeSO₄ . 7H₂O is heated ?

FeSO₄.7H₂O (hydrated ferrous sulphate or green vitriol) ——-> FeSO₄. H₂O (at 140^o C)
FeSO₄. H₂O ——–>  2 FeSO₄ (at 300 ^o C)

2FeSO₄  ——> Fe₂O₃ + SO₂ + SO₃

Properties of sulphuric acid:

1. Acidic nature:

H₂SO₄ is a strong dibasic acid. It forms two types of salt.

H₂SO₄ +NaOH —–> NaHSO₄ [sodium hydrogen sulphate (acidic salt)] + H₂O

H₂SO₄ + 2NaOH ——-> Na₂SO₄ [sodium sulphate (normal salt)]+ 2H₂O

2. Oxidizing property:

It acts as strong oxidizing agent.

a) It oxidizes carbon to CO₂:

2H₂SO₄ ——> 2H₂O + 2SO₂ + 2[O]

C+ 2[O] —-> CO₂

Equation as a whole- 

2H₂SO₄ + C —-> 2H₂O + 2SO₂ + CO₂

b) It oxidizes sulphur to SO₂ :

2H₂SO4 ——> 2H₂O + 2SO₂ + 2[O]

S + 2[O] —–> SO₂

Equation as a whole- 

2H₂SO4 + S —-> 2H₂O + 3SO₂

c) It oxidizes phosphorus to H₃PO₄:

5H₂SO₄ —–> 5H₂O + 5SO₂ + 5[O]

2P + 5[O] + 3H₂O —–> 2H₃PO₄

Equation as a whole- 

5H₂SO₄ + 2P —–> 5SO₂ + 2H₃PO₄ + 2H₂O

d) It oxidizes KI into I₂

2KI + 2 H₂SO₄ ——> K₂SO₄ + 2H₂O + SO₂ + I₂

e) It oxidizes KBr into Br₂:

2KBr + 2H₂SO₄ ——> K₂SO₄ + H₂O + SO₂ + Br₂

3. As dehydrating agent :

Concentrated H₂SO₄ absorbs water and acts as dehydrating agent. It absorbs H₂O from sugar, starch, paper, wood, cloth etc.

C₆H₁₂O₆ ———> 6C + 2H₂O

(C₆H₁₀O₅)_n   (starch)   ———> 6nC + 5nH₂O

C₁₂H₂₂O₁₁ (sucrose or sugar) ——-> 12C + 11H₂O

4. Reaction with SO₃ :

Oleum is obtained

H₂SO₄ + SO₃ ——> H₂S₂O₇ (oleum)

5. Reaction with PCl₅ :

H₂SO₄ +PCl₅ ——-> SO₃HCl(chloro sulphonic acid)  + POCl₃ ( phosphoryl chloride ) + HCl

H₂SO₄ + 2PCl₅ —–> SO₂Cl₂ (sulphuryl chloride) + 2POCl₃ + 2HCl

6. Reaction of H₂SO₄ with less reactive metal Ag, Hg, Pb, Cu, Sn ?

Ag + H₂SO₄ ——>Ag₂SO₄ +SO₂ +H₂O

Hg + H₂SO₄  ——–> HgSO₄ +SO₂ + H₂O

Cu + H₂SO₄ ——-> CuSO₄ + SO₂ + H₂O

Sn + H₂SO₄ —–> Sn(SO₄)₂ (Stannic sulphate) + SO₂ + H₂O

Pb + H₂SO₄ —–> PbSO₄ + SO₂ + H₂O

Question : What happens when copper react with dilute H₂SO₄ in presence of air or O₂:

2Cu + 2H₂SO₄ (dilute)+ O₂ ——->2 CuSO₄ + 2H₂O

Uses :

1. As dehydrating agent.
2. As an oxidising  agent and  sulphonating agent.
3. In the manufacture of paint.
4. In lead storage battery.
5. In petroleum refining.
6. In the manufacture of explosives such as Trinitrotoluene, nitroglycerine,picric acid etc.