180 GROUP IV(phosgene). COCl 2. is formed :CO + C1 2 -> COCK^Vith ammoniacal or hydrochloric acid solution of copper(I)
chloride, carbon monoxide forms the addition compound CuCl .CO.
2H 2 O. This reaction can be used to quantitatively remove carbon
monoxide from gaseous mixtures.
Although carbon monoxide appears to be the anhydride of
methanoic acid it does not react with water to give the acid; how-
ever, it will react with sodium hydroxide solution above 450 K,
under pressure, to give sodium methanoate:
CO + NaOH -> HCOO~Na+Carbon dioxide, CO 2. Carbon dioxide is present in air and escapes
from fissures in the earth in volcanic regions and where ^mineral
springs' occur. It may be prepared by:
(1) the action of dilute acid on any metal carbonate or hydrogen-
carbonate, for example
CaCO 3 + 2HC1 -> CaCU + CO 2 | + H 2 O
(2) the action of heat on a hydrogencarbonate,
2HCO 3 " -» H 2 O + CO 2 | + COf-
(3) the action of heat on a metal carbonate, other than those of the
alkali metals or barium (see later, p. 185). Industrially, carbon
dioxide is obtained in large quantities by heating limestone:
CaCO 3 '->CaO + CO 2 f
It is obtained as a by-product in the fermentation of sugars to give
alcohols:
C 6 H 1206 ^ 2C 2 H 5 OH + 2C0 2Appreciable quantities are also obtained as a by-product in the
manufacture of hydrogen from naphtha-gaseous hydrocarbons. In
this process the gaseous hydrocarbon and superheated steam under
a pressure of about 10 atmospheres and at a temperature of 1000 K
are passed over a nickel-chromium catalyst. Carbon monoxide and
hydrogen are produced:
CnHm + nH 20 -* nCO+ ^--^ H 2The hydrocarbons used depend on availability. Natural gas is now