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A violet compound of manganese (A) decomposes on heating to liberate oxygen and compounds $(B)$ and $(C)$ of manganese are formed. Compound (C) reacts with $\mathrm{KOH}$ in the presence of potassium nitrate to give compound $B$. On heating compound (C)with conc. $\mathrm{H}_2 \mathrm{SO}_4$ and $\mathrm{NaCl}$, chlorine gas is liberated and a compound (D) of manganese along with other product is formed. Identify compounds A to $\mathrm{D}$ and also explain the reactions involved.
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Verified Answer
Compound (C) on heating with conc. $\mathrm{H}_2 \mathrm{SO}_4$ and $\mathrm{NaCl}$ gives $\mathrm{Cl}_2$ gas, so it is manganese dioxide $\left(\mathrm{MnO}_2\right)$. It is obtained along with $\mathrm{MnO}_4^{2-}$ when $\mathrm{KMnO}_4$ (violet) is heated.
Therefore compounds $\mathrm{A}$ to $\mathrm{D}$ and reactions involved are given as following:
$$
\begin{aligned}
&(\mathrm{A})=\mathrm{KMnO}_4 \quad(\mathrm{~B})=\mathrm{K}_2 \mathrm{MnO}_4\\
&\begin{array}{ll}
\text { (C) }=\mathrm{MnO}_2 & \text { (D) }=\mathrm{MnCl}_2
\end{array}\\
&\underset{\text { [A] }}{\mathrm{KMnO}_4} \stackrel{\Delta}{\longrightarrow} \underset{[\mathrm{B}]}{\mathrm{K}_2} \underset{[\mathrm{C}]}{\mathrm{MnO}_4}+\underset{\mathrm{MnO}_2}{ }+\mathrm{O}_2\\
&2 \mathrm{MnO}_2+4 \mathrm{KOH}+\mathrm{O}_2 \longrightarrow 2 \mathrm{~K}_2 \mathrm{MnO}_4+2 \mathrm{H}_2 \mathrm{O}\\
&\mathrm{MnO}_2+4 \mathrm{NaCl}+4 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow\\
&\mathrm{MnCl}_2+4 \mathrm{NaHSO}_4+2 \mathrm{H}_2 \mathrm{O}+\mathrm{Cl}_2\\
&\text { [D] }
\end{aligned}
$$
Therefore compounds $\mathrm{A}$ to $\mathrm{D}$ and reactions involved are given as following:
$$
\begin{aligned}
&(\mathrm{A})=\mathrm{KMnO}_4 \quad(\mathrm{~B})=\mathrm{K}_2 \mathrm{MnO}_4\\
&\begin{array}{ll}
\text { (C) }=\mathrm{MnO}_2 & \text { (D) }=\mathrm{MnCl}_2
\end{array}\\
&\underset{\text { [A] }}{\mathrm{KMnO}_4} \stackrel{\Delta}{\longrightarrow} \underset{[\mathrm{B}]}{\mathrm{K}_2} \underset{[\mathrm{C}]}{\mathrm{MnO}_4}+\underset{\mathrm{MnO}_2}{ }+\mathrm{O}_2\\
&2 \mathrm{MnO}_2+4 \mathrm{KOH}+\mathrm{O}_2 \longrightarrow 2 \mathrm{~K}_2 \mathrm{MnO}_4+2 \mathrm{H}_2 \mathrm{O}\\
&\mathrm{MnO}_2+4 \mathrm{NaCl}+4 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow\\
&\mathrm{MnCl}_2+4 \mathrm{NaHSO}_4+2 \mathrm{H}_2 \mathrm{O}+\mathrm{Cl}_2\\
&\text { [D] }
\end{aligned}
$$
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