Oxides of N, P and As when dissolves in water to form oxy acids. Oxy acids of Sb and Bi are not stable.
Some important oxy acids:
| Element | Formula of the oxyacid | Name of the oxyacid | Oxidation state of element in oxyacid |
| Nitrogen | H2N2O2 | Hyponitrous acid | +1 |
| HNO2 | Nitrous acid | +3 | |
| HNO3 | Nitric acid | +5 | |
| Phosphorus | H3PO2 | Hypo phosphorus acid | +1 |
| H3PO3 | Phosphorus acid | +3 | |
| H3PO4 | Phosphoric acid | +5 | |
| (HPO4)n | Metaphosphoric acid | +5 | |
| H4P2O7 | Pyrophosphoric acid | +5 | |
| Arsenic | H3AsO3 | Arsenious acid | +3 |
| H3AsO4 | Arsenic acid | +5 | |
| Sb & Bi | No stable acid |
Oxyacids of Nitrogen , HNO3 , Nitric acid
Nitric acid is also known as aqua fortis (meaning strong water) which was given by alchemists.
Methods of preparation
(a) Laboratory preparation
KNO3 + H2SO4 → KHSO4 + HNO3
(b) Birkeland Eyde process
N2 + O2 ⇌ 2NO – 43,200 calories
The formation of nitric oxide is favoured by high temperature thus it is maintained at 3000°C.
The nitric oxide is cooled to 1000oC as to prevent its decomposition. Nitric oxide further combines with O2 .
2NO + O2 → 2NO2
The vapours then passed through water when nitric acid is produced.
2NO2 + H2O → HNO3 + HNO2
3HNO2 → HNO3 + 2NO + H2O
(c) Ostwald’s process (Modern process)
In this process the nitric acid is formed first when NH3 and air passed over platinum gauze at 750 – 900°C
The nitric oxide is then oxidised to NO2 by air which is cooled to 50°C and absorbed in water.
2NO + O2 → 2NO2
3NO2 + H2O → 2HNO3 + NO
Fuming nitric acid
When NO2 is dissolved in conc. nitric acid it forms fuming nitric acid. It is brown in colour. It is obtained by distilling concentrated HNO3 with a little starch.
Physical properties
HNO3 is colourless fuming with pungent smell soluble in water. Nitric acid usually acquires yellow
colour due to its decomposition by sunlight into NO2 .
Chemical properties
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Class 12 Chemistry “The p Block Elements” All Topic Notes Class 12 Chemistry All Chapters Notes
