Question

What mass of magnesium forms when 100,000 A is passed through a MgCl2 melt for 1.00 h if the yield of magnesium is 85% of the theoretical yield?

a) 0.102 kg
b) 0.185 kg
c) 0.220 kg
d) 0.275 kg

Answer 1

The mass of magnesium formed when 100,000 A is passed through a MgCl2 melt for 1.00 h, with an 85% yield, is approximately 0.0107 kg. The option close to answer is a)0.102kg.

Step-by-step explanation:

To calculate the mass of magnesium formed, we need to determine the theoretical yield of magnesium and then multiply it by the yield percentage. The molar mass of Mg is 24.31 g/mol, and the chemical equation shows that 1 mol of Mg is formed per 2 mol of electrons:

2e- + Mg2+ → Mg

First, calculate the number of moles of electrons: 100,000 A × 1 h × (1 C/96500 A) × (1 mol e-/96485 C) = 1.038 mol e-

Now, calculate the moles of Mg: (1.038 mol e-) × (1 mol Mg/2 mol e-) = 0.519 mol Mg

Finally, calculate the mass of Mg: 0.519 mol Mg × 24.31 g/mol = 12.624 g ≈ 0.0126 kg

Since the yield of magnesium is 85%, multiply the mass of Mg by 0.85 to find the actual mass of magnesium formed:

0.0126 kg × 0.85 ≈ 0.0107 kg

Therefore, the mass of magnesium formed is approximately 0.0107 kg.