348 HEAVY METALS OF GROUPS VI, VII, AND VIII(a) The gray-green Cr(OH) 3 dissolves to give a clear yellow
solution.
2Cr(OH) 3 + 3NaOCl + 4NaOH -* 2Na 2 Cr0 4 + 3NaCl + 5H 2 O
The basic Cr 2 O 3 is oxidized to the acidic CrO 3 which forms the
soluble salt with the alkali.
(6) The light buff Mn(OH) 2 is turned black
Mn(OH) 2 + NaOCl ->MnO 2 + H 2 O + NaCl
MnO is oxidized to MnO 2 which is indifferent and forms salts
with neither bases nor acids.
(c) The gray-green Fe(OH) 2 turns reddish brown
2Fe(OH) 2 + NaOCl + H 2 O -+ 2Fe(OH) 3 + NaCl
(d) The reddish brown Fe(OH) 3 is not altered.
(e) The light-colored Co(OH) 2 turns jet black
2Co(OH) 2 + NaOCl + H 2 O -* 2Co(OH) 3 + NaCl
(/) The apple green Ni(OH) 2 turns jet black
2Ni(OH) 2 + NaOCl + H 2 O -+ Ni(OH) 3 + NaCl
- Oxidation in Alkaline Fusion, (a) Melt sodium car-
bonate in a loop on the end of a platinum wire until a colorless
bead is obtained. Dip the bead in a precipitate of MnO 2
obtained as in Experiment 5 (6), and melt it again, holding
it in the outer edge of the flame to come under the oxidizing
influence of the air. (It is better to use a blow-pipe, holding
the bead in the oxidizing part of the flame.) After the bead
is cold it has a green color.
(6) Repeat (a) using Cr(OH) 3 instead of MnO 2. A yellow
bead is obtained.
(c) Prepare a somewhat larger amount of sodium man-
ganate as follows: Melt a mixture of 5 grams of sodium hy-
droxide, 1 gram of potassium nitrate, and 0.1 gram of .man-
ganese dioxide in a small iron crucible and heat it until it
ceases to foam and the crucible is dull red. Cool the crucible
and treat the contents with about 200 cc. of water. A most
intense green solution of sodium manganate is formed. Let
the solution settle in a tall beaker, pour the clear, but intense
green, liquid into another beaker, and reserve it for Experi-
ment 7 (a).