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Question
Explain why nitric acid is kept in a reagent bottle for a long time.
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Solution
Pure nitric acid is unstable to heat or sunlight. In the presence of sunlight, it decomposes even at room temperature.
\[\ce{4HNO3 ->[Heat][Sunlight]4NO2 + 2H2O + O2}\]
This decomposition produces nitrogen dioxide (NO2), a reddish-brown gas, which dissolves in nitric acid and turns it yellow over time. To prevent decomposition, nitric acid is stored in dark-coloured reagent bottles, which reduce its exposure to light and help maintain its purity for a long time.
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