246 OXY-ACIDS AND SALTS OF THE NON-METALSQUESTIONS- When the bromate is tested with silver nitrate why is it nec-
essary to have the solution hot? (Look up solubility of silver
bromate.) - How does dilute H2SO4 react with a pure bromate? Explain,
with reactions, the test for the presence of bromate in the
bromide. - Explain why it would not be possible to free a preparation of
potassium bromide of a little bromate by recrystallization. - Explain why potassium bromate can be readily freed of
bromide by recrystallization.
PREPARATION 36
POTASSIUM CHLORATE, KC10 3
Read the discussion of the hydrolysis of bromine in the pre-
ceding preparation. About one-third of the chlorine in chlorine
water is hydrolyzed. The bleaching power of chlorine is due
directly to the oxidizing action of the hypochlorous acid produced
by the hydrolysis. The formation of chlorate in this prepara-
tion is also a result of the oxidizing action of hypochlorous
acid.
In the action of chlorine with an alkali hydroxide, six equivalents
of the latter must react in order to produce one equivalent of
alkali chlorate. To economize in potassium hydroxide, which is
more expensive than sodium hydroxide, we shall use one equivalent
only of the former and five equivalents of the latter. The five
equivalents of sodium chloride which could be recovered as a by-
product is not of great value, and we shall discard it in this prep-
aration.
Materials: potassium hydroxide, 16 grams 1 ., „ „ „
,. ii-i,.,. > the pellet iorm of
sodium hydroxide, 44 grams J ^
these hydroxides, as free of carbonate as pos-
sible, should be used. Allowing roughly 10 per
cent as water gives the net amounts: KOH, 0.25
F.W.; NaOH, 1.25 F.W.
chlorine, from a cylinder or generated from granu-
lar manganese dioxide and 12 N HC1.