Page 26 - Curriculum Visions Dynamic Book

Nitric acid
Nitric acid (once called aqua fortis, or “strong water”) is a colourless liquid that has been known about for many centuries. Nitric acid attacks all common metals except aluminium and iron. By mixing nitric acid and hydrochloric acid, HCl, to create a mixture known as aqua regia, it is possible to dissolve all metals, including gold and platinum.
Concentrated nitric acid is an oxidising chemical. Some of the oxygen it contains is readily given up to another reactant.
In the atmosphere, oxygen and nitrogen combine with the energy of
a lightning flash to produce oxides of nitrogen. This, in turn, combines with rain and becomes available to green plants as dilute nitric acid, which can be used by plants as a source of nitrogen fertiliser.
Nitric acid is prepared industrially from ammonia and is used to make a wide variety of compounds, from fertilisers and dyes to explosives.
EQUATION: Making nitric acid from ammonia
 Ammonia + oxygen ➪ nitric oxide + water NH3(g) + 5O2(g) ➪ 4NO(g) + 6H2O(aq)  Nitric oxide + oxygen ➪ nitrogen dioxide 2NO(g) + O (g) ➪ 2NO (g)
 Preparing nitric acid This apparatus shows the
preparation of fuming nitric acid from concentrated sulphuric acid and potassium nitrate.
Hot fuming nitric acid is highly corrosive. You will notice that
all of the laboratory equipment being used is glass (rubber stoppers or tubing, for example would simply be corroded away).
The fuming brown gas is nitrogen dioxide.
2 2
 Nitrogen dioxide + water ➪ nitric acid + nitric oxide
3NO (g) + 6H O(aq) ➪ 2HNO (aq) + NO(g) 2 2 3
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