What is the oxidation state of Cr when the pH | vedclass

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Question

(C) In an aqueous solution, potassium dichromate $(K_2Cr_2O_7)$ exists in equilibrium with potassium chromate $(K_2CrO_4)$ depending on the $pH$ of th

Vedclass · Accepted Answer

$6$

Vedclass · Answer

(C) In an aqueous solution, potassium dichromate $(K_2Cr_2O_7)$ exists in equilibrium with potassium chromate $(K_2CrO_4)$ depending on the $pH$ of the solution. The equilibrium reaction is: $Cr_2O_7^{2-} + 2OH^- \rightleftharpoons 2CrO_4^{2-} + H_2O$. In $K_2Cr_2O_7$, the oxidation state of $Cr$ is calculated as: $2(+1) + 2(x) + 7(-2) = 0$ $\Rightarrow 2 + 2x - 14 = 0$ $\Rightarrow 2x = 12$ $\Rightarrow x = +6$. In $K_2CrO_4$, the oxidation state of $Cr$ is calculated as: $2(+1) + x + 4(-2) = 0$ $\Rightarrow 2 + x - 8 = 0$ $\Rightarrow x = +6$. Since the oxidation state of $Cr$ remains $+6$ in both acidic $(Cr_2O_7^{2-})$ and basic $(CrO_4^{2-})$ media, the correct answer is $6$.

What is the oxidation state of $Cr$ when the $pH$ of the aqueous solution of potassium dichromate changes from acidic to basic?

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