244 OXY-ACIDS AND SALTS OF THE NON-METALScal changes occurring in the process, and on it the calculation of
quantities of materials and products is to be based.
The reaction represented in (3) does not take place to an appre-
ciable extent in alkaline or neutral solution, but when the neutral
point is overstepped by a mere trace of acid the reaction readily
completes itself in a few minutes at the boiling temperature. A
little excess of bromine, shown by a reddish color, gives, by virtue
of the hydrolysis above mentioned, the requisite degree of acidity.
The following train of equations gives an idea of the way in which
this trace of bromine promotes the reaction. It will be noticed
that in equation (9) the bromine used in equation (5) is regener-
ated, so that a trace of bromine working over and over again
suffices to convert all the hypobromite into bromate. The addi-
tion of all the equations (5) to (9) in the train gives the equation
(10) for the total net change which is identical to equation (3)
Br 2 + H 2 O -» HBr + HBrO (5)
HBr + KBrO -» KBr + HBrO (6)
2HBrO + KBrO -»• KBrO 3 + 2HBr (7)
HBr + KBrO -»• KBr + HBrO (8)
HBrO + HBr -> Br 2 + H 2 O (9)
3KBrO -» KBrO 3 + 2KBr (10)
Materials: potassium hydroxide, 0.5 F.W. = 28 grams; this
material should be as nearly free from carbonate
as possible. Since it is very deliquescent it will
doubtless contain water, and a somewhat greater
weight than 28 grams will have to be taken. Take
31 grams if the analysis of the material is not
known.
bromine, 40 grams = 12.5 cc. = 0.25 F.W. Br 2
charcoal, 5 grams.
Apparatus: 300-cc. Erlenmeyer flask.
400-cc. iron crucible,
suction filter and trap bottle.
2.5-inch funnel.
4-inch porcelain dish.
50-cc. graduate,
asbestos paper,
iron ring and ring stand.
Bunsen burner.