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|
|Phosphorus||H3PO2||Hypo phosphorus acid||+1|
|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.
HNO3 is colourless fuming with pungent smell soluble in water. Nitric acid usually acquires yellow
colour due to its decomposition by sunlight into NO2 .
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