Question

Determine the. oxidation state of chromium in the finfll product formed by the reaction between KI and acidified potassium dichromate solution.

• A. + 3
• B. 2
• C. 1
• D. -3

Answer 1

The correct option is A + 3

K would not be expected to be in the final NET equation since K+ is a spectator ion; i.e., it does not react. When you put KI into water it dissolves and splits up into K+ and I- ions. Only the I- participates in the redox reaction. It wouldn't matter whether you used KI or NaI.
Oxidation: $2I^{-}\to I^2+2e^{-}$
Reduction: $C{r}_2{O}_7^{2-}+14H^{+}+6e^{-}\to 2C{r}^{3+}+7H_{2}O$

The final product formed is :
$6I^{-}+C{r}_2{O}_7^{2-}+14H^{+}---->3I_2+2C{r}^{3+}+7H_{2}O$
Calculating the oxidation state of chromium we get + 3