Chemistry Reference
In-Depth Information
●
Mixtures
Many everyday things are not pure substances,
they are mixtures. A mixture contains more than
one substance (elements and/or compounds).
An example of a common mixture is sea water
(Figure 2.10).
Figure 2.9
This is a modern infrared spectrometer. It is used in analysis
to obtain a so-called fi ngerprint spectrum of a substance that will allow
the substance to be identifi ed.
Infrared spectroscopy is used by the pharmaceutical
industry to identify and discriminate between drugs
that are similar in structure, for example penicillin-
type drugs. Used both with organic and inorganic
molecules, this method assumes that each compound
has a unique infrared spectrum. Samples can be solid,
liquid or gas and are usually tiny. However, Ne, He,
O
2
, N
2
or H
2
cannot be used.
This method is also used to monitor environmental
pollution, and has biological uses in monitoring
tissue physiology including oxygenation, respiratory
status and blood fl ow damage.
Forensic scientists make use of both these
techniques because they are very accurate but they
only require tiny amounts of sample - often only
small amounts of sample are found at crime scenes.
Other techniques utilised are nuclear magnetic
resonance spectroscopy and ultraviolet/visible
spectroscopy.
Figure 2.10
Sea water is a common mixture.
Other mixtures include the air, which is a mixture
of elements such as oxygen, nitrogen and neon and
compounds such as carbon dioxide (see Chapter 11,
p. 173), and alloys such as brass, which is a mixture
of copper and zinc (for a further discussion of alloys
see Chapter 10, p. 165).
What is the difference between
mixtures and compounds?
There are differences between compounds and
mixtures. This can be shown by considering the
reaction between iron fi lings and sulfur. A mixture
of iron fi lings and sulfur looks different from the
individual elements (Figure 2.11). This mixture has
the properties of both iron and sulfur; for example, a
magnet can be used to separate the iron fi lings from
the sulfur (Figure 2.12).
Substances in a mixture have not undergone
a chemical reaction and it is possible to separate
them provided that there is a suitable difference
in their physical properties. If the mixture of iron
and sulfur is heated a chemical reaction occurs and
a new substance is formed called iron(ii)
ii
) sulfi de
(Figure 2.11). The word equation for this reaction is:
iron + sulfur
Questions
1
Write the word and balanced chemical equations for the
reactions which take place between:
a
calcium and oxygen
b
copper and oxygen.
2
Write down the ratio of the atoms present in the formula
for each of the compounds shown in Table 2.5.
3
Iron is extracted from iron(
iii
) oxide in a blast furnace by a
redox reaction. What does the term 'redox reaction' mean?
4
Identify the oxidising and reducing agents in the following
reactions:
a
copper(
ii
) oxide
+
hydrogen
→
copper
+
water
b
tin(
ii
) oxide
+
carbon
→
tin
+
carbon dioxide
c
PbO(
s
)
+
H
2
(
g
)
→
Pb(
s
)
+
H
2
O(
l
)
heat
iron(ii)
ii
) sulfi de
