SULFUR
&
CONTACT PROCESS
G2 Lesson
Sulfur
Sulfur is a really important and abundant (common) non-metallic
element. It is vital in a number of industrial processes.
The element was known to many ancient civilisations and was a
key ingredient in gunpowder.
Sources of sulfur
In the past, sulfur was mined from large underground beds in
many countries around the world.
Now, it is produced as a by-product of the oil-refining industry.
Volcanic activity can also result in sulfur being deposited in its
native form, for example on the rims of volcanoes. This can be
collected and used on a small scale
A man
carrying sulfur
from a
volcano.
Sulfur compounds
Sulfur is usually found as a compound. Sulfur compounds form
impurities, which are present in fossil fuels.
Sulfur is an extremely useful element and is used industrially in the
production of concrete, pesticides and medicines. A key industrial
use of sulfur is in the production of sulfuric acid.
Sulfur dioxide is used to bleach paper white and to preserve foods
like apricots.
Properties of sulfuric acid
Sulfuric acid (H2SO4) is one of
the most widely used acids
in industry. It is a strong acid
and forms salts called
sulfates.
When concentrated, it forms
a thick, brown liquid.
Concentrated sulfuric acid is
highly corrosive. The reason
for this is that it acts as a
dehydrating agent. Sulfuric
acid gives out heat energy
during the dehydration
reaction (exothermic).
H2SO4 + C6H12C6
DEMO
Manufacture of sulfuric acid - Contact
process
Step 1: sulfur to sulfur dioxide
First, sulfur is burned in the presence of oxygen.
sulfur + oxygen → sulfur dioxide
S(s) + O2(g) → SO2(g)
Manufacture of sulfuric acid - Contact
process
Step 2: sulfur dioxide to sulfur trioxide
The sulfur dioxide is then mixed with air and allowed to pass
over a catalyst (vanadium (V) oxide).
sulfur dioxide + oxygen ⇌ sulfur trioxide
2SO2(g) + O2(g) ⇌ 2SO3(g)
An excess of air is used is to ensure that all of the sulfur dioxide is
reacted. High temperature of 450 °C. The forward reaction is
exothermic, so low temp = higher yield (but slow).
High pressure shift equilibrium, but high costs and dangerous normally less than 2 atm used .
Manufacture of sulfuric acid - Contact
process
Step 3: sulfur trioxide to sulfuric acid
The sulfur trioxide is then dissolved in conc sulfuric acid to form
oleum. This is a thick, fuming liquid. Finally, water is added to the
oleum to make concentrated sulfuric acid.
sulfur trioxide + water → sulfuric acid
SO3(g) + H2O(l) → H2SO4(aq)
Uses of sulfuric acid
● Most sulfuric acid produced is used to make fertilisers
(ammonium sulfate).
● The chemical industry accounts for the rest of the consumption of
sulfuric acid.
○ Detergents, resins, paints, dyes and other pigments are all key
products that rely on the acid. Most non-ferrous car batteries
will also contain sulfuric acid.
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