Modern inorganic chemistry

338 GROUP VII: THE HALOGENS

can be displaced to the right by the removal of the halide ion. X ~~.

or the hydrogen ion, H 3 O +. Thus the halic(I) acids can be prepared

by (a) passing the halogen into alkali (provided that disproportiona-

tion of the halate(I) can be minimised), or by (b) passing the halogen

into a well-stirred suspension of yellow mercury(11) oxide, which

removes the halide ion as insoluble mercury(II) halide:

C1 2 + 2H 2 O ^ HC1O 4- H 3 O+ + Cl~ (11.5)

HgO + 2H + + 2CP -* H 2 O + HgCl 2 (11.6)

All the halic(I) acids are unstable in aqueous solution with respect

to disproportionation, the stability decreasing from chloric(I) to

iodic(F):

3HXO -> 2HX + HXO 3

The acids are only known in aqueous solution; all are oxidising

agents; the standard redox potentials for the reaction

HXO + H+ + 2e~ -> X" + H 2 O
are:
X - Cl, E*= + 1.49V

X = Br, E^= 4- 1.33V

X = I, E^= -f 0.99V

The stability of the halate(I) ion decreases, as expected, from
CIO" to IO~ and only the chlorate(I) ion can be considered reason-
ably stable even in aqueous solution. Solid sodium bromate(I).
NaBrO (with five or seven molecules of water of crystallisation)
can be obtained, but on standing or warming it disproportionates:

3BrO^ -> BrOj 4- 2Br~

The aqueous solution of sodium chlorate(I) is an important liquid
bleach and disinfectant. It is produced commercially by the electroly-
sis of cold aqueous sodium chloride, the anode and cathode products
being mixed. The sodium chloride remaining in the solution does
not usually matter. There is evidence to suggest that iodic(I) acid
has some basic character

IOH r + OH~

and iodine monochloride, ICI. can be prepared by reacting iodic(I)
acid with hydrochloric acid.