Question

The brownish yellow color of nitric acid is removed by:
A: Bubbling air through warm acid
B: Bubbling acid
C: Passing ammonia through acid
D: Adding little $Mg$ powder

Answer 1

Hint: Chemical formula of nitric acid is $HN{O_3}$. The yellow color of the nitric acid is directly proportional to the extent of dissolved oxides of nitrogen. This color can be reduced by using some chemical techniques.

Complete step by step answer:
Chemical formula of nitric acid is $HN{O_3}$. Nitric acid is yellow in color because of the presence of oxides of nitrogen. Pure nitric acid undergoes decomposition. Reaction involved is written below:
$4HN{O_3}\xrightarrow[{}]{}2{H_2}O + 4N{O_2} + {O_2}$
As we can see, nitrogen dioxide is formed on decomposition. The color of nitrogen dioxide is reddish brown. This nitrogen dioxide when comes in contact with acid appears yellow in color.
This yellow color of nitric acid can be reduced by using some techniques. The color can be reduced by using air bleaching. To remove this color air is bubbled through acid. This removes nitrogen dioxide which is responsible for the color of nitric acid. This removes nitrogen dioxide when it comes in contact with water and forms nitric acid. Reaction involved is written below:
$3N{O_2} + {H_2}O\xrightarrow{{}}2HN{O_3} + NO$
This means the color of nitric acid can be removed by bubbling air through acid.

So, the correct answer is Option A .

Note:
Chemical formula of nitrogen dioxide is $N{O_2}$. This gas is formed as an intermediate in the industrial synthesis of nitric acid. This gas can be used as a fertilizer. At higher temperature this gas is reddish-brown in color.