The cycle can be completed by bubbling carbon dioxide into the solution. A white precipitate of calcium carbonate is formed. We can complete what is sometimes referred to as the limestone cycle (Figure 1.23).
More detail on the importance of limestone and the chemicals derived from it can be found in Section 9.6. This includes the method of making lime industrially.
pieces of limestone (calcium carbonate)
dropper with water
nothing happens with limestone
limestone
dropper with water wire support
steam
cool
Bunsen flame
quicklime limestone changes into quicklime (calcium oxide)
slaked lime is formed from quicklime
heatproof mat
Figure 1.22 The formation of quicklime and slaked lime in the laboratory.
add carbon dioxide (this is the test for CO2)
calcium carbonate (limestone)
carbon dioxide given off
calcium hydroxide solution (limewater)
add more water and filter
heat
calcium oxide (lime or quicklime)
add a little water calcium hydroxide (slaked lime)
Figure 1.23 The limestone cycle.
Chapter 1
Planet Earth
17