Synthetic Inorganic Chemistry

EXPERIMENTS 295

In the same way that the higher oxide SnO 2 is more acidic than
SnO, the higher sulphide SnS2 is more acidic and reacts more easily
with the basic sulphide, Na 2 S.
Addition of an acid displaces the very weak thio-stannic acid
from its salt solution, 2HC1 + Na 2 SnS 3 -»• 2NaCl + H 2 SnS 3 ; this
acid is very unstable and decomposes into stannic sulphide, the
yellow precipitate, and hydrogen sulphide, H 2 SnS 3 —* H 2 S f +
SnS 2 i.

12. Lead Dioxide, (a) To 2 cc. of Pb(NO 3 ) 2 solution add
    5 cc. of water and 6 2V NaOH until the precipitate first formed
    redissolves. Then add chlorine water and note the dark
    brown precipitate.
    (b) Collect the precipitate on a filter, wash it with water,
    break the tip of the filter, and wash the precipitate with a jet
    from the wash bottle into a test tube. Shake the test tube
    and divide the suspension equally among four tubes. Add
    to the respective tubes (1) 62V HNO 3 , (2) 62V H 2 SO 4 , (3) 62V
    HC1, (4) 62V NaOH, and note that nitric and sulphuric acids
    have no effect, hydrochloric acid dissolves the brown precip-
    itate with evolution of chlorine, and sodium hydroxide has
    no effect.

Chlorine in alkaline solution oxidizes the divalent lead to tetra-

valent, the latter appearing as the very insoluble brown PbO 2

Na 2 Pb0 2 + Cl 2 -»2NaCl + PbO 2 j

This highest oxide of lead has practically no basic properties

and it does not react with nitric and sulphuric acids. Neither are

its acidic properties highly developed, for it does not react with

NaOH in solution. The action with HC1 has already been dis-

cussed; it depends on the reducing action of this acid. The

next experiment, however, throws a little more light on this sub-

ject.

13. Lead Tetrachloride. Cool to 0° 5 cc of 122V HC1 in
    a test tube, and keeping the solution cold add about 1 gram
    of dry lead dioxide a little at a time with shaking. Note that
    a clear yellow solution is formed. Add a drop or two of this
    solution to 500 cc. of cold water in a large beaker and note an
    opalescent brown precipitate which rather slowly becomes