Discussion
Consider the following anodic (oxidation) reaction in an acidic solution:
\[ Mg \longrightarrow Mg^{+2} + 2e^{-} \]
If 48250 Coulomb charge is produced during this anodic reaction then the amount of Mg (in g) dissolved into the solution is
(Given: Faraday Constant =96500 C/mole of electrons, Atomic weight of Mg = 24)
Answer: A
The mass of Mg dissolved is 6 g.
By Faraday's law the charge gives the moles of electrons, and each Mg atom releases two electrons:
\[ \begin{aligned} n_{e} &= \frac{48250}{96500} = 0.5\ \text{mol} \\ n_{\text{Mg}} &= \frac{0.5}{2} = 0.25\ \text{mol} \\ m &= 0.25 \times 24 = 6\ \text{g} \end{aligned} \]
12 g forgets the factor of two electrons per Mg atom, and 24 and 48 g would need two and four times the charge given.
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