Question

What is the quantity of electricity in Coulombs required to produce 4.8 g of Mg from molten MgCl₂? How much Ca will be produced if the same amount of electricity was passed through molten CaCl₂? (Atomic mass of Mg = 24 u, atomic mass of Ca = 40 u).

Answer 1

\[\ce{Mg^{2+} + 2e- -> Mg}\]

1 mole of magnesium ions gains two moles of electrons or 2F to form 1 mole of Mg 24 g Mg requires 2F electricity.

4.8 g Mg requires `2 × 4.8/24` = 0.4F = 0.4 × 96500 = 38600 C

\[\ce{Ca^{2+} + 2e^{-} -> Ca}\]

2F electricity is required to produce 1 mole = 40 g Ca

0.4F electricity will produce 8 g Ca.