Synthetic Inorganic Chemistry

310 ELEMENTS OF GROUP V

QUESTIONS

1. Treat a fragment of antimony trichloride with water. Why
   does it not give a clear solution? Add HC1. Why does this cause
   a clear solution to be formed?


2. Pass hydrogen sulphide into the solution of antimony tri-
   chloride. What is the color of the precipitate? How could it be
   converted into a product like stibnite?


3. Compare the reactions of phosphorus, arsenic, and antimony
   trichlorides with water. Is hydrolysis more complete or less
   complete in the case in which a precipitate forms?

PREPARATION 57

SODIUM SULPHANTIMONATE, Na 3 SbS4-9H 2 O

The oxides of arsenic and antimony, and more particularly the

higher oxides, are acidic in nature, and form salts with basic oxides.

3Na 2 O + As 2 O 3 = 2Na 3 As0 3

3Na 2 O + As 2 O 6 = 2Na 3 As0 4

Sulphur, in accord with its similarity to oxygen, can be substituted

for it in many of its compounds without essentially altering their

chemical nature, and the compounds thus obtained have the

same nomenclature as the corresponding oxygen compounds, except

that the prefix thio or sulpho is used. Thus sulpho-salts are

produced in the same manner as the oxy-salts above:

3Na 2 S + As 2 S 3 = 2Na 3 AsS 3

3Na 2 S + As 2 S 6 = 2Na 3 AsS 4

The sulpho-salts of arsenic, antimony, and stannic tin are particu-
larly characteristic of these metals. (See Preparation 43 and
Experiment 11, page 294.) They are easily produced, and all
are soluble. They are stable in neutral or basic solutions, but are
decomposed by acids, because the anions of the salts combine with
hydrogen ions to produce the very weak sulpho-acids, which, being
unstable, decompose at once into the sulphides of the metals and
hydrogen sulphide:

6H+ + 2AsS 3 """ -* 2H 3 AsS 3 -* 3H 2 S + As 2 S 3 j

6H+ + 2AsS 4 ~~~ -• 2H 3 AsS 4 -• 3H 2 S + As 2 S 61