Question

Aluminium oxide may be electrolysed at 1000°C to furnish
aluminium metal (At. Mass = 27 amu; 1 Faraday = 96,500
Coulombs). The cathode reaction is– Al³⁺ + 3e⁻ → Al
To prepare 5.12 kg of aluminium metal by this method we
require electricity of
(a) 5.49 × 10¹ C (b) 5.49 × 10⁴ C
(c) 1.83 × 10⁷ C (d) 5.49 × 10⁷ C

Answer 1

answer : option (d) 5.49 × 10⁷ C

The cathode reaction is ––> Al³⁺ + 3e⁻ → Al

here it is clear that, To deposit one mole of aluminium metal, three moles of electrons are required.

we know from Faraday's law,

one mole of electrons is equivalent with 96500 C charge.

so, 3 moles of electrons is equivalent with 3 × 96500 C charge.

now no of mole of Al = 5.12 kg/27 g/mol

= 5.12 × 1000g/27 mol

= 5120/27

now total electricity require to deposit 5.12 kg of aluminium metal = number of mole of Al × 3 × 96500 C

= 5120/27 × 3 × 96500 C

= 54,897,777.8 ≈ 5.49 × 10⁷ C

hence option (d) is correct choice.

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