Fig. 7.1 : Flow diagram for manufacture of Sulfuric acid
i. Sulfur or sulfide ore (iron pyrites) on
burning or roasting in air produces sulfur
dioxide.
S(s) + O 2 (g) ∆ SO 2 (g)
4FeS 2 (s) + 11O 2 (g) ∆ 2Fe 2 O 3 (s) + 8SO 2 (g)
ii. Sulfur dioxide is oxidised catalytically
with oxygen to sulfur trioxide, in the presence
of V 2 O 5 catalyst.
2SO 2 (g) + O 2
V 2 O 5
2SO 3 (g)The reaction is exothermic and reversible
and the forward reaction leads to decrease
in volume. Therefore low temperature (720K)
and high pressure (2 bar) are favourable
conditions for maximum yield of SO 3.
iii. Sulfur trioxide gas (from the catalytic
converter) is absorbed in concentrated
H 2 SO 4 to produce oleum.
Dilution of oleum with water gives sulfuric
acid of desired concentration.
SO 3 (g) + H 2 SO 4 H 2 S 2 O 7
oleum
H 2 S 2 O 7 + H 2 O 2H 2 SO 4
The sulfuric acid obtained by contact process
is 96 - 98 % pure.
b. Physical properties of H 2 SO 4 :
i. Sulfuric acid is a colourless, dense, oily
liquid.
ii. It has a density (specific gravity) of 1.84
g/cm^3 at 298 K.
iii. It freezes at 283 K and boils at 611 K.
iv. It is highly corrosive and produces severe
burns on the skin.Do you know?
Sulfuric acid dissolves in water
with the evolution of a large quantity
of heat. Hence care must be taken while
preparing solution of sulfuric acid from
concentrated sulfuric acid. Concentrated
H 2 SO 4 must be added slowly to water with
constant stirring by keeping the beaker in
water bath.c. Chemcial Properties :
i. Acidic Property : Sulfuric acid ionises in
aqueous solution in two steps.
H 2 SO 4 (aq)+H 2 O(l) H 3 O⊕(aq)+HSO 4 (aq)
Ka > 10
HSO 4 (aq)+ H 2 O(l) H 3 O⊕(aq) + SO 42 (aq)
Ka = 1.2 × 10-2
The greater value of Ka (Ka>10) means that
H 2 SO 4 is largely dissociated into H⊕ and
HSO 4 ions. Thus H 2 SO 4 is a strong acid.
ii. Reaction with metals and nonmetals
(oxidising property) : Metals and nonmetals
both are oxidised by hot, concentrated sulfuric
acid which itself gets reduced to SO 2.
Cu + 2H 2 SO 4 CuSO 4 + SO 2 + 2H 2 O
(Conc.)