Question

How many Faradays are required to reduce 1 mol of \(Cr_2O_7^{2-}\) to \(Cr^{3+}\) in acidic medium ?

• A. 2
• B. 3
• C. 6
• D. 4

Hint:

The number of Faradays equals the number of moles of electrons transferred. One Faraday is the charge of one mole of electrons.

Answer 1

The Correct Option is C

Step 1: Understand Faraday.
The number of Faradays needed equals the number of moles of electrons that move in the reaction.

Step 2: Find the oxidation states.
In \(Cr_2O_7^{2-}\), each Cr is \(+6\). It is reduced to \(Cr^{3+}\), which is \(+3\).

Step 3: Electrons per chromium.
Going from \(+6\) to \(+3\) means each Cr gains \(3\) electrons.

Step 4: Count both chromium atoms.
There are \(2\) Cr atoms in \(Cr_2O_7^{2-}\), so total electrons \(= 2 \times 3 = 6\).

Step 5: Conclusion.
Six moles of electrons are needed, hence \(6\) Faradays.

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