Question

Manganese$\left(IV\right)$oxide, lead$\left(IV\right)$oxide, and red lead$\left({\mathrm{Pb}}_3{\mathrm{O}}_4\right)$ react with concentrated hydrochloric acid liberating chlorine.
What is the common property being shown by these metal oxides?

Answer 1

• Manganese oxide$\left({\mathrm{MnO}}_2\right)$, lead oxide$\left({\mathrm{PbO}}_2\right)$, and red lead$\left({\mathrm{Pb}}_3{\mathrm{O}}_4\right)$ all these oxides act as oxidizing agents so they will oxidize $\mathrm{HCl}$ by liberating chlorine.
  $$\begin{gathered} {\mathrm{MnO}}_{2_{\left(\mathrm{s}\right)}}+4{\mathrm{HCl}}_{\left(\mathrm{aq}\right)}\to {{\mathrm{MnCl}}_2}_{\left(\mathrm{aq}\right)}+2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+{{\mathrm{Cl}}_2}_{\left(\mathrm{g}\right)} \\ {\mathrm{PbO}}_{2_{\left(\mathrm{s}\right)}}+4{\mathrm{HCl}}_{\left(\mathrm{aq}\right)}\to {{\mathrm{PbCl}}_2}_{\left(\mathrm{aq}\right)}+2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+{{\mathrm{Cl}}_2}_{\left(\mathrm{g}\right)} \\ {\mathrm{Pb}}_3{\mathrm{O}}_{4_{\left(\mathrm{s}\right)}}+8{\mathrm{HCl}}_{\left(\mathrm{aq}\right)}\to {3{\mathrm{PbCl}}_2}_{\left(\mathrm{aq}\right)}+4{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+{{\mathrm{Cl}}_2}_{\left(\mathrm{g}\right)} \end{gathered}$$
• This is because metals $\mathrm{Mn}$, and $\mathrm{Pb}$ are less electronegative than chlorine and oxidize $\mathrm{HCl}$ catalytically by air to form elemental chlorine gas.