240 HEAVY METALS OF GROUPS I AND IIprecipitate. Collect each precipitate on a filter, wash it with
hot water, and then pour over it a few cubic centimeters of
GNKCl.
The precipitates are CuS, dark brown; Ag 2 S, black; ZnS, white;
CdS, yellow; HgS + Hg, black; and HgS, black. Of these only
zinc sulphide and cadmium sulphide dissolve in 6 N HC1.
(6) To 1 cc. of 1N ZnSO 4 add 10 cc. of water and 1 cc. of
6N HC1, and pass hydrogen sulphide in until the solution
is saturated with the gas. No precipitate is formed. Add
10 cc. of 1N NaAc and observe the white precipitate.Zinc sulphide does not precipitate from an acidified solution
because the S~~ ion concentration is repressed by the H+ ions of
the strong acid, H 2 S ^± 2H+ + S~~, and the solubility product of
zinc sulphide cannot be reached. Acetate ions, however, remove
H+ ions, and, the hydrogen sulphide thus being allowed to ionize
to a greater extent, the solubility product of zinc sulphide is ex-
ceeded and the white precipitate appears. (See Solubility Prod-
uct, page 131, and Experiment 22, page 175.)
- Electromotive Series. Review Experiment 19, page 92,
and make what further experiments of a similar nature are necessary
to determine the relative position in the electromotive series of the
heavy metals considered in this chapter.
GENERAL QUESTIONS VII
HEAVY METALS OF GROUPS I AND II- Make a table as follows. In column 1 give the symbols of
the metals — copper (leave two lines), silver, gold (two lines), zinc,
cadmium, and mercury (two lines); in column 2, the formulas of
the chlorides; in column 3, the solubility of the chloride, speci-
fying sol = soluble, ins = insoluble; in column 4, the formula of
the oxide corresponding to the chloride in column 2; in column 5,
the formula of the corresponding nitrate, if one exists; in column 6,
the degree of hydrolysis of the chloride or nitrate, whichever is
soluble, specifying none, little, large. - Give all available information as to the stability of the car-
bonates of the metals of this chapter. Compare the base-forming
properties of these metals among themselves, and also with the
alkali metals, the alkaline earth metals, and aluminum.