solves in water to give *carbonic
acid.
Large quantities of solid carbon
dioxide (dry ice) are used in processes
requiring large-scale refrigeration. It
is also used inÜre extinguishers as a
desirable alternative to water for
mostÜres, and as a constituent of
medical gases as it promotes exhala-
tion. It is also used in carbonated
drinks.
The level of carbon dioxide in the
atmosphere has increased by some
12% in the last 100 years, mainly be-
cause of extensive burning of fossil
fuels and the destruction of large
areas of rain forest. This has been
postulated as the main cause of the
average increase of 0.5°C in global
temperatures over the same period,
through the *greenhouse effect.
Steps are now being taken to prevent
further increases in atmospheric CO 2
concentration and subsequent global
warming.carbon disulphide (carbon bisul-
phide)A colourless highly refractive
liquid, CS 2 , slightly soluble in water
and soluble in ethanol and ether; r.d.
1.261; m.p. –110°C; b.p. 46.3°C. Pure
carbon disulphide has an ethereal
odour but the commercial product is
contaminated with a variety of other
sulphur compounds and has a most
unpleasant smell. It was previously
manufactured by heating a mixture
of wood, sulphur, and charcoal; mod-
ern processes use natural gas and sul-
phur. Carbon disulphide is an
excellent solvent for oils, waxes, rub-
ber, sulphur, and phosphorus, but its
use is decreasing because of its high
toxicity and itsÛammability. It is
used for the preparation of xanthates
in the manufacture of viscose yarns.carbonÜbres Fibres of carbon in
which the carbon has an oriented
crystal structure. CarbonÜbres are
made by heating textileÜbres andare used in strong composite ma-
terials for use at high temperatures.carbonic acidA dibasic acid,
H 2 CO 3 , formed in solution when car-
bon dioxide is dissolved in water:
CO 2 (aq) + H 2 O(l) ˆH 2 CO 3 (aq)
The acid is in equilibrium with dis-
solved carbon dioxide, and also disso-
ciates as follows:
H 2 CO 3 ˆH++ HCO 3 –
Ka= 4.5 × 10 –7mol dm–3
HCO 3 – ˆCO 3 2–+ H+
Ka= 4.8 × 10 –11mol dm–3
The pure acid cannot be isolated,
although it can be produced in ether
solution at –30°C. Carbonic acid gives
rise to two series of salts: the *car-
bonates and the *hydrogencarbon-
ates.carbonium ionSee carbocation.carbonize(carburize)To change an
organic compound into carbon by
heating, or to coat something with
carbon in this way.carbon monoxideA colourless
odourless gas, CO, sparingly soluble
in water and soluble in ethanol and
benzene; d. 1.25 g dm–3(0°C); m.p.
–199°C; b.p. –191.5°C. It isÛammable
and highly toxic. In the laboratory it
can be made by the dehydration of
methanoic acid (formic acid) using
concentrated sulphuric acid. Industri-
ally it is produced by the oxidation of
natural gas (methane) or (formerly)
by the water-gas reaction. It is
formed by the incomplete combus-
tion of carbon and is present in car-
exhaust gases.
It is a neutral oxide, which burns
in air to give carbon dioxide, and is a
good reducing agent, used in a num-
ber of metallurgical processes. It has
the interesting chemical property
of forming a range of transition
metal carbonyls, e.g. Ni(CO) 4. Car-
bon monoxide is able to use vacantcarbon disulphide 102c