Q. Al₂O₃ is reduced by electrolysis at low potentials and high currents. If 4.0 × 10⁴ amperes of current is passed through molten Al₂O₃ for 6 hours, what mass of aluminium is produced? (Assume 100% current efficiency. At. mass of Al = 27 g mol⁻¹)
A) 8.1 × 10⁴ g
B) 2.4 × 10⁵ g
C) 1.3 × 10⁴ g
D) 9.0 × 10³ g
Explanation
[Solution from source] Charge Q = 4.0 × 10⁴ × 6 × 3600 = 8.64 × 10⁸ C. Al³⁺ + 3e⁻ → Al, so moles of Al = 8.64 × 10⁸/(3 × 96500) ≈ 2984 mol, mass ≈ 2984 × 27 ≈ 8.1 × 10⁴ g. Forgetting the factor 3 gives 2.4 × 10⁵ g. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.