COMPOUNDS OF NITROGEN WITH OXYGEN AND HYDROGEN
In addition to ammonium hydroxide, nitrogen forms several compounds with hydrogen and oxygen, of which nitric acid (HNO3) and nitrous acid (HNO2) are the most familiar.
Nitric acid (HNO3). Nitric acid is not found to any extent in nature, but some of its salts, especially sodium nitrate (NaNO3) and potassium nitrate (KNO3) are found in large quantities. From these salts nitric acid can be obtained.
Fig. 37
Preparation of nitric acid. When sodium nitrate is treated with concentrated cold sulphuric acid, no chemical action seems to take place. If, however, the mixture is heated in a retort, nitric acid is given off as a vapor and may be easily condensed to a liquid by passing the vapor into a tube surrounded by cold water, as shown in Fig. 37. An examination of the liquid left in the retort shows that it contains sodium acid sulphate (NaHSO4), so that the reaction may be represented by the equation
NaNO3 + H2SO4 = NaHSO4 + HNO3.
If a smaller quantity of sulphuric acid is taken and the mixture is heated to a high temperature, normal sodium sulphate is formed:
2NaNO3 + H2SO4 = Na2SO4 + 2HNO3.
In this case, however, the higher temperature required decomposes a part of the nitric acid.