Page 36 - Curriculum Visions Dynamic Book

Nitric acid
Nitric acid (once called aqua fortis, or “strong water”), a colourless liquid, is the most important nitrogen acid, and has been known about for many centuries. Concentrated nitric acid is an oxidising chemical. The oxygen it contains is readily given up to other reactants.
Nitric acid attacks all common metals except aluminium and iron. By mixing nitric acid and hydrochloric acid, HCl, to give a mixture known as aqua regia, it is possible to dissolve all metals, including gold and platinum.
In the atmosphere, hydrogen and nitrogen combine, given the energy of a lightning flash, to produce ammonia. This in turn combines with rain and becomes available to green plants as dilute nitric acid. Dilute nitric acid 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 fuming nitric acid
Preparing nitric acid
This apparatus shows the preparation of fuming nitric acid from concentrated sulphuric acid and potassium nitrate.
Hot fuming nitric acid is incredibly corrosive, so you will notice that all of the laboratory equipment being used is glass (there are no rubber stoppers or tubing for example).
The fuming gas produced when some nitric acid decomposes at this very high temperature is nitrogen dioxide and water vapour formed together with oxygen.
Concentrated sulphuric acid
Concentrated sulphuric acid + potassium nitrate ➪ nitric acid + potassium hydrogen sulphate
H2SO4(l)
+ KNO3(s)
Potassium nitrate
Hydrogen
Oxygen
Sulphur
➪ HNO3(g) + KHSO4(s) ◆
◆
+➡+ Potassium
Nitrogen
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