Chemistry Reference
In-Depth Information
●
Sulfur dioxide
Sulfur dioxide is a colourless gas produced when
sulfur or substances containing sulfur, for example
crude oil or natural gas, are burned in oxygen gas. It
has a choking smell and is extremely poisonous. The
gas dissolves in water to produce an acidic solution of
sulfurous acid.
sulfur dioxide
SO
2
(
g
)
+
+
water
H
2
O(
l
)
sulfurous acid
H
2
SO
3
(
aq
)
This solution turns moist universal indicator paper
red. It is one of the major pollutant gases and is the
gas principally responsible for
acid rain
. However, it
does have some uses: as a bleaching agent for paper
manufacture, in fumigants and in the preservation of
food by killing bacteria.
Sulfur dioxide will turn acidifi ed potassium
manganate(
vii
) solution from purple to colourless
(Figure 12.2).
Figure 12.3
This forest has been devastated by acid rain.
in acidity has led to extensive damage to forests
(Figure 12.3), lakes and marine life.
In addition it has led to the increased corrosion
of exposed metals and to damage to buildings and
statues made from limestone or marble (Figure 12.4).
The sulfurous acid in rainwater oxidises to sulfuric
acid. The sulfuric acid reacts with the limestone,
which is eaten away by the chemical process.
limestone
+
sulfuric acid
calcium
sulfate
CaSO
4
(
s
)
+
water
+
carbon
dioxide
CO
2
(
g
)
→
CaCO
3
(
s
)
+
H
2
SO
4
(
aq
)
+
H
2
O(
l
)
+
→
Figure 12.2
Test for sulfur dioxide.
Figure 12.4
Acid rain is responsible for much of the damage to this
temple on the Acropolis in Athens.
Question
1
'Sulfur is a non-metallic element.' Discuss this statement,
giving physical and chemical reasons to support your
answer.
The amount of sulfur dioxide in the atmosphere has
increased dramatically over recent years. There has
always been some sulfur dioxide in the atmosphere,
from natural processes such as volcanoes and rotting
vegetation. Over Europe, however, around 80%
of the sulfur dioxide in the atmosphere is formed
from the combustion of fuels containing sulfur
(Figure 12.5). After dissolving in rain to produce
sulfurous acid, it reacts further with oxygen to form
sulfuric acid.
Acid rain
Rainwater is naturally acidic since it dissolves carbon
dioxide gas from the atmosphere as it falls. Natural
rainwater has a pH of about 5.7. In recent years,
especially in central Europe, the pH of rainwater has
fallen to between pH 3 and pH 4.8. This increase
