Q.Write chemical reactions for differen steps in the manufacture of sulphuric acid by lead chamber process. Draw the structure of phosphorus pentachloride.

SO3 is trigonal planar with three sigma bonds and no lone pair on S -> sp2 hybridisation.

In sulphur trioxide, the central sulphur atom forms three sigma bonds to three oxygen atoms and has no lone pair. The number of electron domains around S is 3, which corresponds to sp2 hybridisation and a trigonal …

Oleum, or fuming sulphuric acid, has the formula $H_2S_2O_7$.

When sulphur trioxide ($SO_3$) is absorbed in concentrated sulphuric acid ($H_2SO_4$) during the Contact Process, it forms pyrosulphuric acid, commonly called oleum:

$H_2SO_4 + SO_3 \longrightarrow H_2S_2O_7 \ (\text{oleum})$

Oleum is a fuming liquid because on contact with atmospheric moisture it regenerates $H_2SO_4$, releasing visible white fumes:

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H2SO4 gives two H+ ions, so it is dibasic.

Basicity of an acid = number of replaceable hydrogen atoms (ionisable protons) it can furnish. H2SO4 ionises in two steps:

H2SO4 → H+ + HSO4^-

HSO4^- → H+ + SO4^2-

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Oleum = H2SO4 + SO3 (fuming sulphuric acid, H2S2O7).

In the Contact process, SO3 is absorbed in concentrated H2SO4 to give oleum (pyrosulphuric acid, H2S2O7), rather than being absorbed directly in water:

H2SO4 + SO3 → H2S2O7 (oleum)

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