Chemistry Reference
In-Depth Information
The units for measuring mass are grams (g) and
kilograms (kg).
Generally colloids cannot be separated by filtration
since the size of the dispersed particles is smaller
than that of the pores found in the filter paper.
Look closely at the substances shown in Figure 2.35
to see examples of these mixtures.
1 kg = 1000 g
When using an electronic balance you should wait
until the reading is steady before taking it.
Measurement of volume
a
These jelly-like mixtures of solid
and liquid in fruit jelly and cold
custard are examples of 'gels'.
b
Emulsion paint is an
example of a 'sol'.
Figure 2.34
The apparatus shown in the photograph is generally used in
different experiments to measure volume accurately.
c
These foams have been formed by
trapping bubbles of gas in liquids or
solids.
d
Emulsions are formed by
mixing immiscible liquids.
Different experiments involving liquids will require
one or other or all the various measuring apparatus
for volume. The volume of a liquid is a measure of
the amount of space that it takes up. The units of
volume are litres (l) and cubic centimetres (cm
3
).
Figure 2.35
When you mix a solid with a liquid you sometimes
get a gel. A gel is a semi-solid which can move
around but not as freely as a liquid. Within a gel the
solid makes a kind of network which traps the liquid
and makes it unable to flow freely (Figure 2.36).
1 litre = 1000 cm
3
However, some of the manufacturers of apparatus
used for measuring volume use millilitres (ml). This is
not a problem, however, since 1 cm
3
= 1 ml.
When reading the volume using one of the pieces
of apparatus it is important to ensure that the
apparatus is vertical and that your eye is level with the
top of the meniscus of the liquid being measured.
network of
gelatine molecules
water molecules trapped
in a network of gelatine
●
Gels, sols, foams and
emulsions
Gels, sols, foams and emulsions are all examples
of mixtures which are formed by mixing two
substances (or phases) which cannot mix. These
mixtures are often referred to as
colloids
. Colloids
are formed if the suspended particles are between
1 nm and 1000 nm in size (1 nm = 1 × 10
−9
m).
Figure 2.36
The network within a gel.
