Question:
What is the oxidation state of chromium in the final product when KI reacts with acidified potassium dichromate solution?
What is the oxidation state of chromium in the final product when KI reacts with acidified potassium dichromate solution?
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Dichromate oxidises iodide to iodine and itself becomes Cr3+.
Updated On: Oct 1, 2026
- \(+2\)
- \(+3\)
- \(+6\)
- \(+4\)
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The Correct Option is B
Solution and Explanation
Step 1: Write the reaction
Acidified \(K_2Cr_2O_7\) oxidises \(I^-\) to \(I_2\): \(Cr_2O_7^{2-} + 14H^+ + 6I^- \rightarrow 2Cr^{3+} + 3I_2 + 7H_2O\).
Step 2: Oxidation state
In \(Cr_2O_7^{2-}\) chromium is \(+6\). The product \(Cr^{3+}\) has oxidation state \(+3\), so each Cr gains 3 electrons.
Step 3: Other options
\(+6\) is the starting value and \(+2\) or \(+4\) are not formed in this reaction.
Final Answer:
Chromium ends as Cr(III), oxidation state +3. \[ \boxed{\text{(B)}\ +3} \]
Acidified \(K_2Cr_2O_7\) oxidises \(I^-\) to \(I_2\): \(Cr_2O_7^{2-} + 14H^+ + 6I^- \rightarrow 2Cr^{3+} + 3I_2 + 7H_2O\).
Step 2: Oxidation state
In \(Cr_2O_7^{2-}\) chromium is \(+6\). The product \(Cr^{3+}\) has oxidation state \(+3\), so each Cr gains 3 electrons.
Step 3: Other options
\(+6\) is the starting value and \(+2\) or \(+4\) are not formed in this reaction.
Final Answer:
Chromium ends as Cr(III), oxidation state +3. \[ \boxed{\text{(B)}\ +3} \]
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