copper(II) nitrateA blue deliques-
cent solid, Cu(NO 3 ) 2 .3H 2 O; r.d. 2.32;
m.p. 114.5°C. It may be obtained by
reacting either copper(II) oxide or
copper(II) carbonate with dilute nitric
acid and crystallizing the resulting
solution. Other hydrates containing 6
or 9 molecules of water are known.
On heating it readily decomposes to
give copper(II) oxide, nitrogen diox-
ide, and oxygen. The anhydrous form
can be obtained by reacting copper
with a solution of nitrogen dioxide in
ethyl ethanoate. It sublimes on heat-
ing suggesting that it is appreciably
covalent.copper(I) oxideA red insoluble
solid, Cu 2 O; r.d. 6.0; m.p. 1235°C. It is
obtained by reduction of an alkaline
solution of copper(II) sulphate. Since
the addition of alkalis to a solution of
copper(II) salt results in the precipita-
tion of copper(II) hydroxide the cop-
per(II) ions are complexed with
tartrate ions; under such conditions
the concentration of copper(II) ions is
so low that the solubility product of
copper(II) hydroxide is not exceeded.
When copper(I) oxide reacts with
dilute sulphuric acid a solution of
copper(II) sulphate and a deposit of
copper results, i.e. disproportionation
occurs.
Cu 2 O + 2H+→Cu2++ Cu + H 2 O
When dissolved in concentrated
hydrochloric acid the [CuCl 2 ]–com-
plex ion is formed. Copper(I) oxide is
used in the manufacture of rectiÜers
and the production of red glass.copper(II) oxideA black insoluble
solid, CuO; monoclinic; r.d. 6.3; m.p.
1326 °C. It is obtained by heating ei-
ther copper(II) carbonate or copper(II)
nitrate. It decomposes on heating
above 800°C to copper(I) oxide and
oxygen. Copper(II) oxide reacts read-
ily with mineral acids on warming,
with the formation of copper(II) salts;it is also readily reduced to copper on
heating in a stream of hydrogen.
Copper(II) oxide is soluble in dilute
acids forming blue solutions of
cupric salts.copper pyritesSee chalcopyrite.copper(II) sulphateA blue crys-
talline solid, CuSO 4 .5H 2 O; triclinic;
r.d. 2.284. The pentahydrate loses
4H 2 O at 110°C and theÜfth H 2 O at
150 °C to form the white anhydrous
compound (rhombic; r.d. 3.6; decom-
poses above 200°C). The pentahy-
drate is prepared either by reacting
copper(II) oxide or copper(II) carbon-
ate with dilute sulphuric acid; the so-
lution is heated to saturation and the
blue pentahydrate crystallizes out on
cooling (a few drops of dilute sul-
phuric acid are generally added to
prevent hydrolysis). It is obtained on
an industrial scale by forcing air
through a hot mixture of copper and
dilute sulphuric acid. In the pentahy-
drate each copper(II) ion is sur-
rounded by four water molecules at
the corner of a square, theÜfth and
sixth octahedral positions are occu-
pied by oxygen atoms from the sul-
phate anions, and theÜfth water
molecule is held in place by hydro-
gen bonding. Copper(II) sulphate has
many industrial uses, including the
preparation of the Bordeaux mixture
(a fungicide) and the preparation of
other copper compounds. It is also
used in electroplating and textile
dying and as a timber preservative.
The anhydrous form is used in the
detection of traces of moisture.
Copper(II) sulphate pentahydrate is
also known as blue vitriol.coprecipitation The removal of a
substance from solution by its associ-
ation with a precipitate of some
other substance. For example, if A
and B are present in solution and a
reagent is added such that A formscopper(II) nitrate 144c