Synthetic Inorganic Chemistry

334 HEAVY METALS OP GROUPS VI, VII, AND VIII

capable of combining with bases to form molybdates which are

analogous to sulphates. The alkali metal and ammonium salts of

molybdic acid are soluble. The calcium salt is sparingly soluble.

Materials: molybdenum trioxide, MoO 3 , 5 grams.

6.ZVNaOH, 12 cc.

QN HNO 3.

calcium chloride, anhydrous, 3.8 grams,

litmus paper.

Apparatus: 250-cc. beaker.

2.5-inch funnel.

Procedure: Dissolve 5 grams of MoO 3 in 12 cc. of 6N NaOH.

Barely neutralize with QN HNO3, using litmus as indicator.

The neutral point must not be overstepped if a precipitate of

molybdic acid is to be avoided. Dissolve 3.8 grams of anhydrous

calcium chloride in 9 cc. of water and stir this into the sodium

molybdate solution. Collect the precipitate, wash it with cold

water, and dry it on the steam table (80-100°) over night.

PREPARATION 68

AMMONIUM TUNGSTATE, (NH 4 ) 2 WO4

Tungsten like chromium and molybdenum is acidic in its high-

est valence, WO3, and forms salts known as tungstates.

Materials: tungstic oxide, WO 3 , 23.2 grams = 0.1 F.W.

15 N NH4OH, 50 cc.

Apparatus: 250-cc. beaker.

4-inch evaporating dish.

4-inch iron ring and ring stand.

2.5-inch funnel.

Procedure: Digest the tungstic oxide with 40 cc. of 15 N NH4OH
for 10 minutes at 50°. Pour off the clear solution, and if a solid
residue is left digest it repeatedly with 5-cc. portions of the NH4OH,
adding the extract to the main solution. Filter, if necessary,
directly into the evaporating dish. Let stand at about 80° until
dry. Save the needle shaped crystals in a 2-ounce, cork-stoppered
bottle.