222 HEAVY METALS OF GROUPS I AND IIcentrated sulphuric acid. Analyze this reaction, and show in
what manner the copper is oxidized.- How can copper sulphate be obtained from copper sulphide
on a commercial scale?
PREPARATION 28
CUPROUS CHLORIDE, CuCl
Cupric salts derived from the oxide CuO are stable in contact
with air and water and comprise the most used compounds of
copper. Cupric ions, Cu++, are present in solutions of cupric salts.
Cuprous salts are derived from cuprous oxide, Cu 2 O, and are
generally unstable in contact with air and water. No soluble
cuprous salts which dissolve in water to give cuprous ions, Cu+,
are known.
The conditions under which cuprous salts can exist may be ex-
plained in terms of the equilibrium which establishes itself in the
reaction
Cu° + Cu++ <=t 2Cu+ (1)
When copper metal is dipped in cupric sulphate solution this
reaction runs a very small distance to the right until the equilib-
rium ratio of cuprous and cupric ions is reached. This ratio is
very small. The same concentration ratio is reached from the
opposite direction when cuprous oxide is treated with dilute sul-
phuric acid
Cu 2 O + H 2 SO 4 -»• 2Cu+ SO«~~ + H 2 O
2Cu+ <=t Cu++ + Cu
when nearly all the cuprous sulphate resulting from the neutrali-
zation changes to cupric sulphate and copper.
Cuprous ions and chloride ions form two different combinations
Cu+ + Cl" ^ CuCl | (2)
Cu+ + 2C1" ^ CuCl 2 " (3)
In presence of chloride ions, Cu+ ions are thus removed and copper
can continue to react with Cu++ ions as in (1) until the cupric
salt is all reduced to cuprous. Increasing concentration of Cl"
favors reaction (3) more than reaction (2), and thus in con-
centrated HC1 we obtain the soluble H+CuCl 2 ~. Dilution of the
latter reduces the concentration of (Cl~), which favors the com-
plex ion formation in proportion to its second power, and of the