On balancing the given redox reaction, aCr _2 O _7^ 2- + bSO _3^ 2- ( aq )+ cH ^ + ( aq ) 2 aCr ^ 3+ ( aq )+ bSO _4^ 2- ( aq )+ c 2 H _2 O ( l ) the coefficients a, b and c are found to be, respectively-

On balancing the given redox reaction, aCr _2 O _7^ 2- + bSO _3^ …

MCQ

On balancing the given redox reaction,

$aCr _2 O _7^{2-}+ bSO _3^{2-}( aq )+ cH ^{+}( aq ) \rightarrow 2 aCr ^{3+}( aq )+ bSO _4^{2-}( aq )+\frac{ c }{2} H _2 O ( l )$

the coefficients a, b and $c$ are found to be, respectively-

✓

Correct option: B.

$1,3,8$

b
Using Ion electron method :

Reduction Half reaction : $Cr _2 O _7^{2-}+6 e ^{-} \longrightarrow 2 Cr ^{3+}$

Oxidation Half reaction: $SO _3^{2-} \longrightarrow SO _4^{2-}+2 \overline{ e } \times 3$

Overall reaction : $Cr _2 O _7^{2-}+3 SO _3^{2-} \longrightarrow 2 Cr ^{3+}+3 SO _4^{2-}$

- To balance 'O' atoms, adding $H _2 O$ on LHS

$Cr _2 O _7^{2-}+3 SO _3^{2-} \longrightarrow 2 Cr ^{3+}+3 SO _4^{2-}+4 H _2 O$

- To balance 'H' atoms, adding $H ^{+}$on $RHS$

$Cr _2 O _7^{2-}+3 SO _3^{2-}+8 H ^{+} \longrightarrow 2 Cr ^{3+}+3 SO _4^{2-}+4 H _2 O$

$\therefore \quad a =1$

$b =3$

$c =8$

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