Question

Nitric acid turns a paper soaked in Potassium iodide solution brown due to liberation of:

• A. Iodine
• B. Nitrogen dioxide
• C. Copper
• D. Hydrogen iodide

Answer 1

The correct option is A

Iodine

A: Iodine

1. Nitric acid is a occurs strong oxidizing agent.
2. When a paper is soaked inside Potassium iodide solution chemical reaction occurs which liberates the iodine from it by oxidizing the other compounds.
3. The products formed are Potassium nitrate$\mathbf{\left(}{\mathbf{KNO}}_{\mathbf{3}}\mathbf{\right)}$, Water, Nitric oxide$\mathbf{\left(}\mathbf{NO}\mathbf{\right)}$, and Iodine.
4. Due to the liberation of Iodine, paper looks brown in color.
5. The chemical reaction is as follows:$\underset{(\mathrm{Potassium}\mathrm{iodide})}{6\mathrm{KI}\left(l\right)}+\underset{(\mathrm{Nitric}\mathrm{acid})}{8{\mathrm{HNO}}_3\left(l\right)}\to \underset{(\mathrm{Potassium}\mathrm{nitrate})}{6{\mathrm{KNO}}_3\left(aq\right)}+\underset{\left(\mathrm{Water}\right)}{4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{(\mathrm{Nitric}\mathrm{oxide})}{2{\mathrm{NO}}_2\left(g\right)}+\underset{\left(\mathrm{Iodine}\right)}{{\mathrm{I}}_2\left(\mathrm{g}\right)}$
6. Hence, by liberation of iodine, the paper soaked in Nitric acid $\mathbf{\left(}{\mathbf{HNO}}_{\mathbf{3}}\mathbf{\right)}$ and Potassium iodide$\mathbf{\left(}\mathbf{KI}\mathbf{\right)}$ mixture turns it to brown color.
7. So option A is correct. Nitric acid turns a paper soaked in Potassium iodide solution brown due to liberation of Iodine.

B: Nitrogen dioxide

1. According to the chemical reaction involved, the paper soaked in a mixture of Potassium iodide$\mathbf{\left(}\mathbf{KI}\mathbf{\right)}$ and Nitric acid$\mathbf{\left(}{\mathbf{HNO}}_{\mathbf{3}}\mathbf{\right)}$ liberates brown colored iodine.
2. This is responsible for turning the color of paper to brown. So option B is incorrect.

C: Copper

1. The chemical reaction of Potassium iodide$\mathbf{\left(}\mathbf{KI}\mathbf{\right)}$ and Nitric acid$\mathbf{\left(}{\mathbf{HNO}}_{\mathbf{3}}\mathbf{\right)}$ involves only the liberation of iodine of brown color
2. Therefore, there is no use for Copper. so option C is incorrect.

D: Hydrogen iodide

1. To turn the paper brown in color the chemical reaction may involve Potassium iodide$\mathbf{\left(}\mathbf{KI}\mathbf{\right)}$ and Nitric acid$\mathbf{\left(}{\mathbf{HNO}}_{\mathbf{3}}\mathbf{\right)}$.
2. The reaction does not involve hydrogen iodide on any of the side, so option D is incorrect.