Question

6. Name a yellow-colored oxide that is insoluble in dilute sulphuric acid.

Answer 1

Step 1: Test cations using an alkali base.

When Lead cation${\mathrm{Pb}}^{+}$ is heated with Ammonium hydroxide${\mathrm{NH}}_4\mathrm{OH}$, it produces a yellow-coloured oxide PbO which is insoluble in dilute sulphuric acid${\mathrm{H}}_2{\mathrm{SO}}_4$.

When this precipitate of Lead oxide PbO is made to react with Sulfuric acid, it forms a thin protective coating of Lead sulfate ${\mathrm{PbSO}}_4$ on the surface of the metal oxide. It is due to this protective coating that the metal oxide becomes insoluble in Sulfuric acid. The following reaction is observed:

$$\begin{gathered} \mathrm{PbO}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{PbSO}}_4+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Lead}\mathrm{Sulfuric}\mathrm{Lead}\mathrm{Water} \\ \mathrm{oxide}\mathrm{acid}\mathrm{sulfate} \end{gathered}$$

Final Answer: The yellow insoluble oxide is PbO.