KCET · Chemistry · Biomolecules

Impure copper containing Fe, Au, Ag as impurities is electrolytically refined. A current of \( 140 \mathrm{~A} \)
for \( 482.5 \mathrm{~s} \) decreased the mass of the anode by \( 22.26 \mathrm{~g} \) and increased the mass of cathode by
\( 22.011 \mathrm{~g} \). Percentage of iron in impure copper is
(Given molar mass \( \mathrm{Fe}=55.5 \mathrm{~g} \mathrm{~mol}^{-1} \), molar mass \( \mathrm{Cu}=63.54 \mathrm{~g} \mathrm{~mol}^{-1} \) )

A \( 0.85 \)
B \( 0.90 \)
C \( 0.95 \)
D None of the above

Verified Solution

Answer & Solution

Correct Answer

(D) None of the above

Step-by-step Solution

Detailed explanation

No. of gram equivalents of copper deposited \(=\frac{22.011}{31.77}\)
\(=0.6298\)
No. of gram equivalents from the current \((Q)\)
\(=I \times t=140 \times 482.5=67550 C\)
No. of gram equivalents \(=\frac{67550}{96500}=0.7\)
Since only Cu and Fe are dissolved from the anode no. of gram equivalents of Fe
\(=0.7-0.6928\)
\(=0.0072\)
Therefore, mass of Fe \(=0.0072 \times 27.75\)
\(=0.1998 g\)
\(\%\) of Fe \(=\frac{\text { Mass of Fe }}{\text { Mass of impurities }} \times 100\)
\(=\frac{0.1998}{22.26}=0.89\) or \(0.89 \%\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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