Question

Find the number of faradays of electricity required to produce 45 g of Al from molten $Al_2O_3$.

(At. mass of Al = 27)

• A. 1 F
• B. 3 F
• C. 5 F
• D. 7 F

Answer 1

Answer: (C)

5 F

Answer 2

To find the number of Faradays required:

1. Calculate moles of Al:

   $$\text{Moles of Al} = \frac{45\text{ g}}{27\text{ g/mol}} = \frac{5}{3} \text{ moles}$$

2. Find moles of electrons needed: The half-reaction for the production of Al is:

   $$\text{Al}^{3+} + 3e^- \longrightarrow \text{Al}$$

   Each mole of Al requires 3 moles of electrons.

   $$\text{Moles of electrons} = \frac{5}{3} \times 3 = 5 \text{ moles}$$

3. Determine Faradays: 1 Faraday corresponds to 1 mole of electrons. Thus, 5 moles of electrons equals 5 Faradays.