GROUP VII: THE HALOGENS 323
fluorine monoxide (see below); in the gas phase ozone and oxygen
are produced3H 2 O + 3F 2 ^6HF + O 3Recent work indicates the existence offluoric(l) acid. HFO, formed
by the reaction of fluorine and water at 273 K. The acid forms
colourless crystals, m.p. 156K, is very unstable, and has, as ex-
pected, very strong oxidising properties.
Chlorine and bromine are both moderately soluble in water, and
on crystallisation these solutions give solid hydrates with the
halogen molecules occupying cavities within a modified ice lattice.
Iodine is only slightly soluble in water in which it forms a brown
solution (brown solutions are also formed in ether, alcohol and
acetone). The aqueous solutions of chlorine and bromine are good
oxidising agents. Chlorine, and to a lesser extent bromine, reacts
reversibly with water to give a mixture of acids, for example :C1 2 + H 2 O ^ HC1O 4- HC1
i.e. chloric(I) + hydrochloric
acid acid
The presence of chloric(I) acid makes the properties of "chlorine
water' different from those of gaseous chlorine, just as aqueous
sulphur dioxide is very different from the gas. Chloric(I) acid is a
strong oxidising agent, and in acid solution will even oxidise
sulphur to sulphuric acid; however, the concentration of free
chloric(I) acid in 'chlorine water' is often low and oxidation reactions
are not always complete. Nevertheless when "chlorine' bleaches
moist litmus, it is the chloric(I) acid which is formed that produces
the bleaching. The reaction of chlorine gas with aqueous bromide
or iodide ions which causes displacement of bromine or iodine (see
below) may also involve the reaction
2r + HC1O + HC1 -> 2CP + I 2 + H 2 O
since water is present to produce the two acids. Chlorine water
loses its efficiency as an oxidising agent on standing because the
chloric(I) acid decomposes. There are two possible ways of de-
composition :3HC1O -* 2HC1 + HC1O 3
chloric(V)
acidor 2HC1O -> 2HC1 + O 2
The second reaction is favoured by sunlight and by catalysts such
as platinum black or metallic oxides (cf. the decomposition of