Modern inorganic chemistry

412 THE TRANSITION ELEMENTS

On heating the pentahydrate, four molecules of water are lost

fairly readily, at about 380 K and the fifth at about 600 K; the

anhydrous salt then obtained is white; the Cu2+ ion is now sur-

rounded by sulphate ions, but the d level splitting energy does not

now correspond to the visible part of the spectrum, and the com-

pound is not coloured. Copper(II) sulphate is soluble in water; the

solution has a slightly acid reaction due to formation of

[Cu(H 2 O) 5 OH] + species. Addition of concentrated ammonia

Figure 13.8, Structure oj crystalline CuSO 4 .5H 2 O

solution produces the deep blue solution already mentioned; if

ethanol is then added, dark blue crystals of the ammine

CuSO 4. 4NH 3. H 2 O can be obtained; in these, the four ammonia

molecules are approximately square-planar around the copper, and

the water molecule is above this plane, forming a square pyramid. If

ammonia gas is passed over anhydrous copper(II) sulphate, a

violet-coloured pentammine CuSO 4. 5NH 3 is formed.

Copper(II) sulphate pentahydrate is made on a large scale by

blowing air through a mixture of scrap copper and dilute sulphuric

acid, the air acting as an oxidising agent. It is used (in solution) as a

fungicide, a wood preservative, in electroplating and in reprography.

COPPER(ll) NITRATE

If copper is treated with a solution of dinitrogen tetroxide in ethyl
ethanoate (acetate), a blue solution is obtained, which on evapora-