Question

For the redox reaction,
$MnO _{4}^{-}+ C _{2} O _{4}^{2-}+ H ^{+} \longrightarrow Mn ^{2+}+ CO _{2}+ H _{2} O$
the correct coefficients of the reactants for the balanced equation are

	$MnO _{4}^{-}$	$C _{2} O _{4}^{2-}$	$H ^{+}$
a	$2$	$16$	$5$
b	$2$	$5$	$16$
c	$16$	$5$	$2$
d	$5$	$16$	$2$

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

The given redox reaction is
$MnO _{4}^{-}+ C _{2} O _{4}^{2-}+ H ^{+} \longrightarrow Mn ^{2+}+ CO _{2}+ H _{2} O$
The reaction can be balanced by considering the following steps;
Step I Balance the atoms except $H$ and $O$.
$MnO _{4}^{-}+ C _{2} O _{4}^{2-}+ H ^{+} \longrightarrow Mn ^{2+}+2 CO _{2}+ H _{2} O$
Step II Write the oxidation number of each atom

Step III Cross multiply by change in oxidation number
$\overset{+7}{Mn}O _{4}^{-} \longrightarrow Mn ^{2+} ; 5 e^{-}$ gain
$\overset{+3}{C _{2}} O _{4}^{2-} \longrightarrow \overset{+4}{2 CO _{2}} ; 2 x 1 e^{-}$ loss
$2 MnO _{4}^{-}+5 C _{2} O _{4}^{-}+ H ^{+} \longrightarrow 2 Mn ^{2+} +10 CO _{2}+ H _{2} O$
Step IV Balance oxygen by adding $H _{2} O$ on deficient site.
$2 MnO _{4}^{-}+5 C _{2} O _{4}^{2-}+ H ^{+} \longrightarrow 2 Mn ^{2+}+10 CO _{2}+8 H _{2} O$
Step V Balance hydrogen
$2 MnO _{4}^{2-}+5 C _{2} O _{4}^{2-}+16 H ^{+} \longrightarrow 2 Mn ^{2+}+10 CO _{2}+8 H _{2} O$
$\therefore$ The coefficients of the reactants, $MnO _{4}^{-}, C _{2} O _{4}^{2-}$ and $H ^{+}$ are $2,5$ and $16$ , respectively.