Question

$9.65C$ of electric current is passed through fused anhydrous magnesium chloride. The magnesium metal thus obtained is completely converted into a Grignard reagent. The number of moles of the Grignard reagent obtained is ___________

• A. $1\times 10^{-4}$
• B. $5\times 10^{-4}$
• C. $1\times 10^{-5}$
• D. $5\times 10^{-5}$

Answer 1

Answer: (D)

$MgC{l}_2⟶M{g}^{2+}+2C{l}^{-}$

$M{g}^{2+}+\underset{2F}{2e^{-}}⟶\underset{1mol}{\mathrm{Mg}}$ at cathode

$\because 2F(2\times 96500C)$ deposits $Mg=1$ mol

$\therefore 9.65C$ charge will deposit $Mg=\frac{1\times 9.65}{2\times 96500}$

$=5\times 10^{-5}$ mol

In order to prepare Grignard reagent, one mole of $Mg$ is used per mole of reagent obtained. Thus, by $5\times 10^{-5}$ mol $Mg,5\times 10^{-5}$ mole of Grignard reagent are obtained.