Chemistry
Explain the following:
(i) Dil. HNO3 is generally considered a typical acid but not so in it's reaction with metals.
(ii) When it is left standing in a glass bottle, concentrated nitric acid appears yellow.
(iii) In the laboratory preparation of nitric acid, an all glass apparatus is used.
Answer
(i) Dilute nitric acid is generally considered a typical acid except for it's reaction with metals since it generally does not liberate hydrogen on reaction with metals. Nitric oxide on decomposition forms nascent oxygen which oxidizes the hydrogen to water.
(ii) Pure nitric acid [HNO3] is colourless and unstable and decomposes slightly even at ordinary temperatures and in the presence of sunlight.
The decomposition results in formation of reddish brown nitrogen dioxide [NO2] which remains dissolved in the acid thus imparting a slight yellowish brown colour.
(iii) All glass apparatus is used since, the vapours of nitric acid being highly corrosive attack rubber, cork. etc.
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