Question

A large electrolysis cell that produces metallic aluminum from Al₂O₃ by the Hall-Héroult process is capable of yielding 900. lb (409 kg) of aluminum in 24 hr. What current is required? Report your answer in scientific notation with three significant figures.

Answer 1

Time, t = 24 hr = 86400 sec

Amount of aluminium produced, m = 409kg = 409000g

Atomic mass of aluminium = 26.98g/mol

Number of moles of aluminium produced = 409000g / 26.98g.mol^-1

= 15159.3773 moles

The process of aluminium from Al₂O₃ involves the following step:

Al³⁺ + 3e^- -----> Al

Therefore, for production of 1mol of aluminium, 3 mol of electrons are required.

So, the number of moles of electrons required = 3 x 15159.3773 = 45478.1319 mol

The charge of 1mol of electron = 96500 C

The charge of 45478.1319 mol of electrons, Q = 96500 x 45478.1319 = 4.39 x 10⁹C

Current = Charge / Time

= (4.39 x 10⁹C) / 86400s

Current = 5.08 x 10⁴ A