Properties sulphuric acid

 Properties sulphuric acid

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What happens when  FeSO. 7H2O is heated ?

FeSO4.7H2O (hydrated ferrous sulphate or green vitriol) ——-> FeSO4. H2O (at 140o 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 SO:

Oleum is obtained

H2SO4 + SO3 ——> H2S2O7 (oleum)

5. Reaction with PCl:

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.