Question

Consider the following reaction:
$M ^{x+}+ MnO _4^{\ominus} \rightarrow MO _3^{\ominus}+ Mn ^{2+}$
If $1\, mol$ of $MnO _4^{\ominus}$ oxidises $1.67\, mol$ of $M ^{x+}$ to $MO _3^{\ominus}$, then the value of $x$ in the reaction is

• A. 2
• B. 3
• C. 4
• D. 5

Answer 1

Answer: (A)

$M ^{x+}+ MnO _4^{\ominus} \longrightarrow MO _3{ }^{\ominus}+ Mn ^{2+}$
$MnO _4{ }^{\ominus}+8 H ^{\oplus}+5 e ^{-} \longrightarrow Mn ^{2+}+4 H _2 O$
$M ^{x+}+3 H _2 O \longrightarrow MO _3{ }^{\ominus}+6 H ^{\oplus}+(5-x) e ^{-}$
$mEq$ of $MnO _4{ }^{2-} \equiv mEq$ of $M ^{x+}$
$1 \times 5 \equiv[1.67 \times(5-x) \Rightarrow 5-x=3 \Rightarrow x=2$