Chemistry 2002 JAMB Past Questions - Question 26: The gas that gives brown colouration in brown ring test is

Correct Answer

C

Explanation

The brown ring test is a chemical test used to detect the presence of the nitrate ion (\(NO_3^-\)) in a solution. The test involves the reaction between a nitrate-containing solution and iron(II) ions in the presence of concentrated sulfuric acid. The gas responsible for the brown coloration in the brown ring test is nitrogen dioxide (\(NO_2\)). The reaction can be represented as follows:

\[ \text{2Fe}^{2+} (aq) + 6HNO_3 (aq) + 12H^+ (aq) \rightarrow 2Fe^{3+} (aq) + 6NO_2 (g) + 6H_2O (l) \]

The brown coloration is due to the formation of the brown complex Fe(NO_2)_6^{3-}, and the nitrogen dioxide gas is evolved.