Barrons SAT Subject Test Chemistry, 13th Edition

Graphite uses the trigonal sp^2 hybrids

Some common amorphous forms of carbon are charcoal, coke, bone black,
and lampblack.

Carbon Dioxide

Carbon dioxide (CO 2 ) is a widely distributed gas that makes up 0.04 percent of

the air. There is a cycle that keeps this figure relatively stable. It is shown in
Figure 37.

Figure 37. Carbon Dioxide Cycle

LABORATORY PREPARATION OF CO 2

The usual laboratory preparation consists of reacting calcium carbonate (marble
chips) with hydrochloric acid, although any carbonate or bicarbonate and any
common acid could be used. The gas is collected by water displacement or air
displacement.
The test for carbon dioxide consists of passing it through limewater,
(Ca(OH) 2 ). If CO 2 is present the limewater turns cloudy because of the formation

of a white precipitate of finely divided CaCO 3 :

Ca(OH) 2 (aq) + CO 2 (g) → CaCO 3 (s) + H 2 O(ℓ)

Continued passing of CO 2 into the solution will eliminate the cloudy condition

because the insoluble CaCO 3 becomes soluble calcium bicarbonate