Modern inorganic chemistry

HYDROGEN 117

TESTS FOR HYDROGEN

In general, hydrogen itself (and compounds containing hydrogen)
when oxidised by heating with oxygen or with a metal oxide form
water, for which tests are available. There are otherwise no chemical
tests for hydrogen. The metal palladium will take up many times its
own volume of hydrogen, to form a non-stoichiometric metal
hydride (p. 113) and this property can be used to separate hydrogen
from other gases which remain unaffected by the palladium.

QUESTIONS

1. Discuss the chemistry of the simple hydrides of the elements,
   indicating how they can be classified according to their structures.
   (Liverpool B Sc.. Part I)


2. (a) Describe in detail the bonding which occurs in the com-
   pounds formed between hydrogen and
   (i) sodium (in sodium hydride),
   (ii) carbon (in methane),
   (iii) nitrogen (in ammonia).
   (b) Describe the reactions, if any, which take place between
   water and the hydrides of the elements in (a).
   (c) Comment upon the significance of the relative values of the
   following boiling points of the halogen hydrides:

HF HC1 HBr HI

19.5 -85 -67 -36 (°Q

(1MB, A)

3. Outline briefly one method for the preparation of each of the
   following:

(a) NaH (from sodium),

(b) CH 4 (from carbon),

(c) PH 4 I (from phosphorus).

How do the following hydrides react with water: NaH, CH 4 , SiH 4
and HI? Comment on these reactions in terms of the nature of the
chemical bonds in these compounds. Suggest reasons for the increase
in acidity in the series PH 3 , H 2 S, HC1. How would you seek to
establish this order experimentally?
(C,A)