Synthetic Inorganic Chemistry

(John Hannent) #1
336 HEAVY METALS OF GROUPS VI, VII, AND VIII

crystal. Let stand undisturbed to aid formation of large crystals.
Drain the crystals, and leave them on a large previously weighed
watch glass to dry. Put the product in a 2-ounce, cork-stoppered
bottle.


QUESTIONS


  1. Dissolve 1-2 grams of the crystals in 15 cc. water. Dilute
    1 cc. stannous chloride solution with 5 cc. hydrochloric acid; add
    1 cc. of this to one-third of the solution of selenious acid. Ob-
    servations? Equations? How do you account for the color?

  2. To another third of the solution of selenious acid, add 5 cc.
    saturated solution of sulphurous acid. Let stand 5 to 10 min-
    utes. Observations? Equations?

  3. To the remainder of the solution add 5 cc. potassium per-
    manganate solution. Observations? Equations? Filter; to the
    colorless nitrate add 5 cc. barium chloride solution. Let settle,
    pour off the supernatent liquid, add 5 cc. 12 N hydrochloric acid
    to the residue and boil for 2 minutes. Dilute to 25 cc. Add 1 to
    2 cc. of sulphurous acid. Observations? Equations?

  4. How would you show the presence of a small amount of
    selenic acid in a large amount of sulphuric acid?


PREPARATION 70
MANGANESE CHLORIDE FROM WASTE MANGANESE LIQUORS
The waste liquors left after the generation of chlorine from
manganese dioxide and hydrochloric acid contain principally
manganous chloride. Besides this, however, there is always some
free acid and almost always a considerable amount of ferric chloride
present. The greater part of the free acid can be removed by
evaporating the solution until a pasty mass is left which will
solidify on cooling. The iron can be removed from the solution of
this residue by virtue of the ease with which ferric salts hydrolyze.
The nearly neutral solution is treated with suspended manganous
carbonate (obtained by treating a part of the solution itself with
a soluble carbonate). Ferric chloride hydrolyzes according to the
reversible reaction, FeCl 3 + 3H 2 O^3HC1 + Fe(OH) 3. In the
presence of manganous carbonate the small amount of free acid
thus formed is continuously used up according to the reaction
MnC0 3 + 2HC1 -• MnCl 2 + H 2 O + CO 2. Thus the reaction of
hydrolysis is enabled to run to completion. The remaining solu-
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