plants. Discharges of lightning also cause some nitrogen fixation with oxygen to
form nitrogen oxides.
Nitric Acid
An important compound of nitrogen is nitric acid. This acid is useful in making
dyes, celluloid film, and many of the lacquers on cars.
Its physical properties are: it is a colorless liquid (when pure), it is one and
one-half times as dense as water, it has a boiling point of 86°C, the commercial
form is about 68% pure, and it is miscible with water in all proportions.
Its outstanding chemical properties are: the dilute acid shows the usual
properties of an acid except that it rarely produces hydrogen when it reacts with
metals, and it is quite unstable and decomposes as follows:
4HNO 3 (aq) → 2H 2 O(l) + 4NO 2 (g) + O 2 (g)Because of this ease of decomposition, nitric acid is a good oxidizing agent.
When it reacts with metals, the nitrogen product formed will depend on the
conditions of the reaction, especially the concentration of the acid, the activity of
the metal, and the temperature. If the nitric acid is concentrated and the metal is
copper, the principal reduction product will be nitrogen dioxide (NO 2 ), a heavy,
red-brown gas with a pungent odor.
Cu(s) + 4HNO 3 (aq) → Cu(NO 3 ) 2 (aq) + 2NO 2 (g) + 2H 2 O(l)With dilute nitric acid, this reaction is:3Cu + 8HNO 3 → 3Cu(NO 3 ) 2 + 4H 2 O+ 2NO(g)The product NO, called nitric oxide, is colorless and is immediately oxidized in
air to NO 2 gas.
With still more dilute nitric acid, considerable quantities of nitrous oxide
(N 2 O) are formed; with an active metal like zinc, the product may be the
ammonium ion (NH 4 +).
When nitric acid is mixed with hydrochloric acid, the mixture is called aqua
regia because of its ability to dissolve gold.
METALS
Properties of Metals
Some physical properties of metals are: they have metallic luster, they can
conduct heat and electricity, they can be pounded into sheets (are malleable), they