Modern inorganic chemistry

418 THE TRANSITION ELEMENTS

Under no conditions is hydrogen obtained from nitric acid. With

the dilute acid, reduction to ammonia occurs:

4Zn + 10HNO 3 -» 4Zn(NO 3 ) 2 4- NH 4 NO 3 + 3H 2 O

i.e. 4Zn 4- 10H + + NO 3 -> 4Zn2+ + NH^ + 3H 2 O

With more concentrated nitric acid, oxides of nitrogen are formed.

Unlike cadmium and mercury and, in fact, all metals of Group II,

zinc dissolves readily in alkalis forming zineates, in which the zinc

atom is contained in a complex hydroxo-anion, for example:

Zn + 2OH" + 4H 2 O -* [Zn(OH) 4 (H 2 O) 2 ]^2 ~ + H 2

At ordinary temperatures, zinc forms an addition compound with

an alkyl halide (cf. magnesium):

Zn + C 2 H 5 I -> C 2 H 5 ZnI

The compound breaks up on heating:

2C 2 H 5 ZnI -> Zn(C 2 H 5 ) 2 + ZnI 2

zinc diethyl

The zinc alkyls, of which this is an example, are vile-smelling

inflammable liquids. They were the first organo-metatlic compounds

prepared by Frankland in 1849. With water, they decompose giving

an alkane:

Zn(C 2 H 5 ) 2 + 2H 2 O -> Zn(OH) 2 + 2C 2 H 6

(Cadmium and mercury also form alkyls.)

Uses

Because of its resistance to corrosion, zinc may be used to coat
iron. This may be done by dipping the iron into molten zinc or by
spraying zinc on the iron articles, for example iron sheets. This is
known as galvanising. Smaller iron articles may be coated by heating
with zinc dust, a process known as sherardising, or suspensions of
zinc may be used in paints.
Sheets of galvanised iron are used for roofing, guttering and the
like. Alloys of zinc, notably brass, are used extensively. The metal
is used in wet and dry Leclanche batteries.
Zinc oxide or kzinc white' is used in paints, but more preferable,
because of its better covering power, is lithopone (a mixture of zinc
sulphide and barium sulphate). Both paints have the advantage
over white lead that they do not 'blacken' in air (due to hydrogen
sulphide). Zinc dust and also zinc chromate are constituents of