ICSE Class 10 Chemistry Question 62 of 63

Study of Compounds — Nitric Acid — Question 62

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Question 3(2020)

State one relevant reason for the following : Concentrated nitric acid appears yellow, when it is left for a while in a glass bottle.

Answer

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.