Modern inorganic chemistry

234 GROUP V

DINITROGEN TR1OX1DE. N 2 O 3

Dmitrogen trioxide, the anhydride of nitrous acid is very unstable,

At low temperature it dissociates thus :

2N 2 O 3 ^ 2NO + N 2 O 4

DINITROGEN PENTOXIDE. N 2 O 5

Dinitrogen pentoxide is the anhydride of nitric acid and is prepared

by removing water from pure nitric acid by means of phosphorus

(V) oxide. It is a crystalline solid having the ionic structure of

(NO 2 )"t"(NO 3 )~, nitronium nitrate (the nitronium ion is mentioned

later). It decomposes above 273 K, thus :

O

Oxides of phosphorus

Phosphorus forms a number of oxides, the best established being
phosphorus(III) oxide, P 4 O 6 , and phosphorus(V) oxide, P 4 O 10 ,
The 4- 5 oxide is the more stable and the + 3 oxide is easily oxidised.

PHOSPHORUS(III) OXIDE, P 4 O 6

Phosphorus(III) oxide is prepared by passing a slow (i.e. limited)
stream of air over burning white phosphorus. A mixture of the two
oxides P 4 O 6 and P 4 O 10 is thereby formed; the (V) oxide can be
condensed out of the emerging gas stream as a solid by passing
through a U tube heated in a water bath to about 330 K; the more
volatile (III) oxide passes on and can be condensed in a second U
trap surrounded by ice.
Phosphorus(III) oxide dissolves in several organic solvents, for
example benzene, carbon disulphide; the molecular weight in these
solvents corresponds to the formula P 4 O 6 , as does the density of
the vapour, and the structure is:

0

0

p^ I p 4

-.ry"/

p

px

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