322 HEAVY METALS OP GKOUPS VI, VII, AND VIIIOn account of the difficulty of carrying out the industrial process
on a laboratory scale, the following less economical procedure is
recommended: The raw material, chromic oxide, Cr 2 O 3 , is first
treated with fused KOH. The oxidizing agent, KNO 3 , is then
added and it works more effectively than if it had been added at
the outset. The aqueous extract of this fusion is allowed to
crystallize to obtain a preparation of potassium chromate. The
mother liquor from these crystals is acidified with acetic acid to
obtain a preparation of potassium dichromate. Potassium com-
pounds are prepared because they are less soluble and crystallize
better than the corresponding sodium compounds.
5Cr 2 O 3 + 14K0H + 6KNO3 = 10K 2 CrO 4 + 7H 2 O + 3N 2
2K 2 Cr0 4 + 2HC 2 H 3 O 2 = K 2 Cr 207 + 2KC 2 H 3 O 2 + H 2 OA saturated solution contains for each 100 grams of water the given
number of grams of the anhydrous salt.Temperature
K2C1O4
K 2 Cr 2070°
59
510°
61
720°
63
1230°
65
2040°
67
2650°
69
3570°
73
55100°
79
88Materials: chromic oxide, Cr 2 O 3 , 50 grams = 0.33 F.W.
potassium hydroxide, 65 grams
potassium nitrate, 50 grams.
glacial acetic acid.
Apparatus: 4-inch sheet iron crucible with cover.
8-inch porcelain dish.
suction filter and trap bottle.
4-inch iron ring and ring stand.
Procedure: Set the iron crucible in a 4-inch iron ring and sup-
port it on a ring stand. Put 65 grams of solid KOH into the
crucible and heat it until the hydroxide is completely melted.
Remove the flame and add 50 grams of chromic oxide, Cr 2 O 3 ,
free from lumps. Stir the mixture with an iron spatula or the wire
end of a test-tube brush. Add 50 grams of finely powdered KN0 3
and stir the mixture until a thin paste is formed. Partially cover
the crucible (leave a i-inch space at one side), and heat the mix-
ture with a flame not more than an inch high. Remove the cover
at frequent intervals to prevent boiling over. After about 15