Question

$9.65\, C$ 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)

$MgCl _{2} \longrightarrow Mg ^{2+}+2 Cl ^{-}$

$Mg ^{2+}+\underset{2F}{2 e^{-}} \longrightarrow \underset{1mol}{Mg}$ at cathode

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

$\therefore 9.65 C$ 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.