Q19 / 160 · AP EAMCET 2003 · Chemistry

During the electrolysis of cryolite, aluminium and fluorine are formed in ........ molar ratio :

  • A
    $1: 2$
  • Correct answer
    B
    $2: 3$
  • C
    $1: 1$
  • D
    $1: 3$

Solution

Electrolysis of cryolite can be explained as $\mathrm{Na}_3 \mathrm{AlF}_6 \rightleftharpoons 3 \mathrm{NaF}+\mathrm{AlF}_3$ $4 \mathrm{AlF}_3 \rightleftharpoons 4 \mathrm{Al}^{3+}+12 \mathrm{~F}^{-}$ $\begin{array}{cc}+12 e^{-} \downarrow & \downarrow-12 e^{-} \\ 4 \mathrm{Al} & 6 \mathrm{~F}_2\end{array}$ (At cathode) (At anode) So, the molar ratio of $\mathrm{Al}$ and $\mathrm{F}_2$ is $4: 6=2: 3$.

Hence, the correct answer is option: 'B'.

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