Making Sulphuric Acid

Raw Materials :

There is no sulphur in the UK, so it has to be imported. It can be extracted from crude oil.

Method :

1) Liquid Sulphur is burned in air

S(l) + O2(g) à SO2(g)

2) The resulting SO2 is oxidised by Oxygen in the Contact Process

2SO2 + O2 à 2SO3

Conditions : 450oC, 1-2 atmospheres, V2O5 catalyst (Vanadium (Roman 5) Oxide

Reaction is exothermic, so previous explanation about yield applies.

High yield is favoured by high pressure, but SO2 liquefies at above 2 atmospheres.

Catalyst increases the yield sharply, but doesn't affect position. Despite this, the yield of SO2 is quite high, and any unused SO2 or O2 are recirculated - it is a continuous process.

Due to the irritation caused by sulphuric acid, precautions have to be taken not to release it into the atmosphere. It is a non-metal oxide and therefore acidic. This problem is solved by lining the tall chimneys with any base - e.g. CaO or CaCO3.This removes the SO2 from the waste gases

3) The reaction of sulphur trioxide with water producing sulphuric acid :

SO3 + H2O à H2SO4

However, this reaction is so vigorously exothermic that it is difficult to control. It produces a mist of tiny droplets of concentrated acid which is almost impossible to condense. To overcome this, SO2 is treated with 98% concentrated sulphuric acid to form an oily compound known as fuming sulphuric acid.

H2SO4 + SO2 à H2S2O7

Water can be safely added to this to produce the end product

H2S2O7 + H2O à 2H2SO4

The first equation can be used as a short hand for these 2 reactions, as long as we remember that is can't be performed directly.

Uses of sulphuric acid :

1) Battery acid

2) Making detergents

3) Making fertilisers in particular, ammonium sulphate in a neutralisation reaction.

2NH3 + H2SO4 à (NH4)2SO4

Concentrated sulphuric acid is also required to make Phosphate fertilisers.
Sulphuric acid is a typical acid reacting with metals, metal oxides and hydroxides, metal carbonates and alkalis to make salts.
Concentrated sulphuric acid is a dehydrating agent, as it has an extreme liking for water.

e.g.1) Concentrated sulphuric acid will remove the water from crystals from hydrated copper sulphate crystals

e.g. 2) Concentrated sulphuric acid has such a strong liking for water that it will demolish molecules of sugars to obtain the elements of the compound water which it absorbs.

This reaction is extremely exothermic and fumes of stems and concentrated H2SO4 are seen. We also see a large increase in volume as a black spongiform of carbon rises up the beaker.

Metal Ores

If we wish to extract a metal from its ore, we need to remove the oxygen (see ore), i.e. perform a reduction reaction.

CuO(s) + H2O(g) à Cu(s) + H2O(g)

black MMMMMMMpink-red

CuO has been reduced as it has lost oxygen.
Cu2+ has been reduced as it has gained electrons.
Hydrogen has been oxidised as it has gained oxygen.
Hydrogen has reacted as a reducing agent as it has caused the CuO to be reduced.
We remember that reducing agents also themselves oxidised.