Question

A black color solid which on reaction with dilute sulphuric acid forms a blue colored solution is:

• A. Carbon
• B. Manganese (IV) oxide
• C. Lead (II) oxide
• D. Copper (II) oxide

Answer 1

The correct option is D

Copper (II) oxide

The correct option is (iv) Copper (II) oxide.

(i) Carbon ($C$) is black but on reacting with diluted Sulphuric acid ($H_{2}S{O}_4$) it gives Carbon dioxide ($C{O}_2$) which is a colorless gas.

$\mathrm{C}\left(\mathrm{s}\right)+\mathrm{dil}.2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

(ii) Manganese (IV) oxide ($Mn{O}_2$) is a brown-black solid but reacting with diluted Sulphuric acid gives a white solid.

$$\begin{gathered} 2{\mathrm{MnO}}_2\left(\mathrm{s}\right)+\mathrm{dil}.2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2{\mathrm{MnSO}}_4\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right) \\ \mathrm{white}\mathrm{solid} \end{gathered}$$

(iii) Lead (II) oxide ($PbO$) is a black solid but on reacting with diluted Sulphuric acid it gives a white solid

$$\begin{gathered} \mathrm{PbO}\left(\mathrm{s}\right)+\mathrm{dil}.{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{PbSO}}_4\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{white}\mathrm{solid} \end{gathered}$$

(iv) Copper (II) oxide ($CuO$) is a black solid. When it reacts with dilute sulphuric acid, it forms a blue-colored solution.

$$\begin{gathered} \mathrm{CuO}\left(\mathrm{s}\right)+\mathrm{dil}.{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{CuSO}}_4\left(\mathrm{l}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{blue}\mathrm{solution} \end{gathered}$$

Copper (II) oxide forms a blue-colored solution with dilute sulphuric acid.