POTASSIUM BROMATE AND POTASSIUM BROMIDE 243that they occur only at the top in the third, fourth, and fifth
groups; and that in the sixth and seventh groups they comprise
all the well-known members of the B families. It is true in these
families, as might be expected by recalling characteristics of
preceding groups, that the strength of the non-metallic character
grows weaker, and that the approach towards metallic character
grows more evident, as the atomic weight increases.
The characteristic valences of the sixth and seventh groups are
6 and 7, respectively, and the corresponding oxides are EO 3
and E 2 O 7. In these oxides and in the compounds derived from
them, there is little dissimilarity between the A and B families.
Thus perchlorates and permanganates are analogous to each
other, as are also sulphates and chromates. In the lower states
of valence, the elements of the B families are entirely differ-
ent from those of the A families, the B family elements forming
exclusively negative ions, S, SC>4, whereas the A family
elements form positive ions, Cr++, Cr+++.
PREPARATION 35
POTASSIUM BROMATE AND POTASSIUM BROMIDE,
KBrO 3 AND KBr
Bromine, like chlorine, hydrolyzes to a considerable extent ac-
cording to the reversible reaction:
Br 2 + H 2 O ^ HBr + HBrO (1)In presence of a base both acids are neutralized as fast as formed
and reaction (1) proceeds to completion. Thus the complete
reaction in presence of KOH is:
Br 2 + 2K0H -» KBr + KBrO + H 2 O (2)Hypobromites are unstable, and, at boiling temperature, and
particularly in slightly acid solution, undergo an action of oxidation
and reduction, the total result of which is:
3KBrO -» KBrO 3 + 2KBr (3)Multiplying equation (2) by 3 and adding equation (3) the equa-
tion
3Br 2 + 6K0H -»• KBrO 3 + 5KBr + 3H 2 O (4)
is obtained. This equation represents the sum total of the chemi-