Chemistry Reference
In-Depth Information
a
At the start of the test.
Figure 13.9
Large-scale production of calcium hydroxide.
This process can be shown on the small scale in
the laboratory by heating a lump of limestone very
strongly to convert it to calcium oxide. Water can
then be carefully added dropwise to the calcium
oxide. An exothermic reaction takes place as the
water and calcium oxide react together in this slaking
process to form calcium hydroxide.
calcium oxide + water → calcium hydroxide
CaO(
s
) + H
2
O(
l
) → Ca(OH)
2
(
s
)
A weak solution of calcium hydroxide in water
is called
limewater
. It is used to test for carbon
dioxide gas, as a white solid of calcium carbonate
is formed if carbon dioxide gas is mixed with it
(Figure 13.10):
calcium + carbon → calcium + water
hydroxide dioxide carbonate
Ca(OH)
2
(
aq
) + CO
2
(
g
) → CaCO
3
(
s
) + H
2
O(
l
)
This brings us full cycle from limestone (calcium
carbonate, CaCO
3
), through calcium oxide (CaO)
and back to calcium carbonate (limestone). This is
known as the 'limestone cycle' (Figure 13.11).
b
The limewater turns cloudy.
c
If the CO
2
is bubbled for longer the white precipitate dissolves.
Figure 13.10
Testing for carbon dioxide.
