Question
How is sulphuric acid prepared industrially by contact process? Support your answer by writing fully balanced chemical equations.
✓
Answer
Contact process for the manufacture of sulphuric acid :
(i) Pure sulphur is burnt in excess of oxygen in sulphur burners to form a mixture of sulphur dioxide and oxygen. The mixture is cooled and then washed with water to remove any dust particles as impurity.
S + O2 → SO2
The moist mixture is dried in conc. sulphuric acid and then passed through arsenic purifier, so as to remove any arsenious oxide present in it. The purified mixture is then passed through a testing box.
(ii) The purified mixture is finally introduced into a catalytic oxidation chamber which contains a series of vertical tubes filled with vanadium pentoxide or platinised asbestos. Sulphur dioxide on coming in contact with the catalyst is oxidised to sulphur trioxide.
$2 SO _2+ O _2 \xrightarrow[\text { at } 450^{\circ} C ]{ V _2 O _{ 5 }} 2 SO _3$
(iii) The sulphur trioxide gas is then absorbed in conc. sulphuric acid to form pyrosulphuric acid or oleum.
$SO _3+ H _2 SO _4$ (conc.) $\longrightarrow H _2 S_2 O _7$
(iv) The pyrosulphuric acid is treated with calculated amount of water to form conc. sulphuric acid.
$H _2 S_2 O _7+ H _2 O \longrightarrow 2 H _2 SO _4$
(i) Pure sulphur is burnt in excess of oxygen in sulphur burners to form a mixture of sulphur dioxide and oxygen. The mixture is cooled and then washed with water to remove any dust particles as impurity.
S + O2 → SO2
The moist mixture is dried in conc. sulphuric acid and then passed through arsenic purifier, so as to remove any arsenious oxide present in it. The purified mixture is then passed through a testing box.
(ii) The purified mixture is finally introduced into a catalytic oxidation chamber which contains a series of vertical tubes filled with vanadium pentoxide or platinised asbestos. Sulphur dioxide on coming in contact with the catalyst is oxidised to sulphur trioxide.
$2 SO _2+ O _2 \xrightarrow[\text { at } 450^{\circ} C ]{ V _2 O _{ 5 }} 2 SO _3$
(iii) The sulphur trioxide gas is then absorbed in conc. sulphuric acid to form pyrosulphuric acid or oleum.
$SO _3+ H _2 SO _4$ (conc.) $\longrightarrow H _2 S_2 O _7$
(iv) The pyrosulphuric acid is treated with calculated amount of water to form conc. sulphuric acid.
$H _2 S_2 O _7+ H _2 O \longrightarrow 2 H _2 SO _4$
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