Chemistry Reference
In-Depth Information
Water has many other important uses besides
sustaining life. These include:
In the home:
●
cooking
●
cleaning
●
drinking.
In industry:
●
as a solvent
●
as a coolant
●
for cleaning
●
as a chemical reactant.
Water is a neutral, colourless liquid which (at
1 atmosphere pressure) boils at 100 °C and freezes at
0 °C (Figure 11.27).
a
Anhydrous copper(
ii
) sulfate goes blue when water is added to it.
b
Cobalt chloride paper turns pink when water is dropped on to it.
Figure 11.28
Tests for the presence of water.
Another test is to dip blue cobalt chloride paper into
the liquid. If the paper turns pink, then the liquid
contains water (Figure 11.28b).
You have already seen in Chapter 5 that water may
be electrolysed (when acidified with a little dilute
sulfuric acid). When this is done, the ratio of the
volume of the gas produced at the cathode to that
produced at the anode is 2 : 1. This is what you might
expect, since the formula of water is H
2
O!
The unique properties of water
Water is a unique substance. Not only is it an
excellent solvent for many ionic substances, such
as sodium chloride, but it also has some unusual
properties. For example:
●
It has an unusually high boiling point for a
molecule of its relatively low molecular mass.
●
It has a greater specific heat capacity than almost
any other liquid.
●
It decreases in density when it freezes (Figure 11.29).
Figure 11.27
Liquid water turns to steam at 100 °C and to ice at 0 °C.
You can find out whether a colourless liquid
contains water by adding the unknown liquid
to anhydrous copper(
ii
) sulfate. If this changes
from white to blue, then the liquid contains water
(Figure 11.28a).
