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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 p Block Elements Chemistry Notes
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 .

The p Block Elements Chemistry Notes
Chemical properties

The p Block Elements Chemistry Notes

The p Block Elements Chemistry Notes

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