Modern inorganic chemistry

GROUPV 241
(1) Non-metals:—These are often oxidised to the corresponding
oxoacid, and nitrogen oxide is formed. For example, sulphur gives
sulphuric acid with cold concentrated nitric acid:

S + 2HNO 3 -> H 2 SO 4 + 2NO

Iodine gives iodic(V) acid with hot concentrated acid:

3I 2 + 10HNO 3 -+ 6HIO 3 + 10NO + 2H 2 O

Fluorine, however, gives the substance 'fluorine nitrate', NO 3 F:

HNO 3 + F 2 -> NO 3 F + HF

Violet phosphorus is oxidised to phosphoric(V) acid.
(2) Metals:—Nitric acid reacts with all common metals except
gold and platinum, but some are rendered passive by the concen-
trated acid, for example aluminium, iron, cobalt, nickel and
chromium. With the very weakly electropositive metals such as
arsenic, antimony and tin, the oxide of the metal in its higher
oxidation state is obtained, for example antimony yields the oxide
antimony(V) oxide, Sb 2 O 5 (in hydrated form). With more electro-
positive metals the nitrate of the metal is always formed, and the
other products vary greatly. Metals which do not liberate hydrogen
from dilute acids form nitrogen oxide or nitrogen dioxide, according
to conditions. For example, copper in cold nitric acid (1:1) reacts
thus:

3Cu + 8HNO 3 -> 3Cu(NO 3 ) 2 + 2NO? + 4H 2 O

In concentrated nitric acid (when warmed) the reaction is:

Cu + 4HNO 3 -> Cu(NO 3 ) 2 + 2NO 2 + 2H 2 O

Metals which do liberate hydrogen from dilute acids, for example
zinc, magnesium, can react with nitric acid to give dinitrogen oxide,
for example:

4Zn 4- 10HNO 3 -* 4Zn(NO 3 ) 2 + N 2 O + 5H 2 O

and if the hydrogen ion content of the nitric acid is further increased,
by adding dilute sulphuric acid, hydroxylamine or ammonia is
formed.
With very dilute nitric acid and magnesium, some hydrogen is
evolved.
With a nitrate in alkaline solution, ammonia is evolved quanti-
tatively by Devarda's alloy (Al, 45%; Cu, 50%; and Zn, 5%). This
reaction can be used to estimate nitrate in absence of ammonium
ions (see below):