Question

What volume of $0.05\, M\, K _2 Cr _2 O _7$ in acidic medium is needed for complete oxidation of $200 \,mL$ of $0.06\, M$ $FeC _2 O _4$ solution?

• A. $1.2 \,mL$
• B. $1.2 \,L$
• C. $120\, mL$
• D. $800 \,mL$

Answer 1

Answer: (B)

$\underset{0.05\,M}{Cr _2 O _7^{2-}}+ \underset{0.6\,M/200\,mL}{FeC _2 O _4 } \xrightarrow{ H ^{\oplus}}$
$Cr _2 O _7^{2-}+14 H ^{\oplus+}+6 e ^{-} \rightarrow 2 Cr ^{3+}+7 H _2 O$
$Fe ^{2+} \rightarrow Fe ^{+3}+ e ^{-}$
$C _2 O _4^{2-} \rightarrow 2 CO _2+2 e ^{-}$
$FeC _2 O _4 \rightarrow Fe ^{3+}+2 CO _2+3 e ^{-}$
$mEq _2$ of $K _2 Cr _2 O _7 \equiv FeC _2 O _4$
$(0.05 \times 6) \times V=(0.6 \times 3) \times 200$
$\Rightarrow V=1200\, mL =1.2\, L$