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Redox Reactions — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryRedox Reactions1 Mark
MCQ
The oxidation state of chromium in the final product formed in the reaction between $KI$ and acidified potassium dichromate solution is:
  • A
    $+4$
  • B
    $+6$
  • C
    $+2$
  • ✓
    $+3$
✓

Answer

Correct option: D.
$+3$
The balanced reaction equation for reaction between potassium iodide and acidified potassium dichromate is :
$\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7+7 \mathrm{H}_2 \mathrm{SO}_4+6 \mathrm{KI} \rightarrow \mathrm{Cr}_2\left(\mathrm{SO}_4\right)_3+3 \mathrm{I}_2+7 \mathrm{H}_2 \mathrm{O}+4 \mathrm{~K}_2 \mathrm{SO}_4$
In this reaction, potassium dichromate gives a chromium sulfate. The oxidation state of chromium in chromium sulfate can be calculated as:
Consider, the oxidation state of $Cr$ be $X$ in $\mathrm{Cr}_2\left(\mathrm{SO}_4\right)_3$
$\therefore  2\text{X} + 3(−2) = 0$
$∴ 2\text{X}−6=0$
$∴ 2\text{X}=6$
$\therefore X=\frac{6}{2}$
$∴X=+3$
Therefore, the oxidation state of $Cr$ in the final product is $+3$.

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