Question

Describe maisson's reaction for the isolation of flourine . Give the modifications done in the origin

Answer 1

Answer on Question #75702 – Chemistry – Inorganic Chemistry

Describe moisson's reaction for the isolation of fluorine. Give the modifications done in the origin.

Solution:

Henri Moissan found a way to produce fluorine by passing an electric current through a liquid mixture of potassium fluoride and hydrogen fluoride. He electrolysed a cooled solution of KF in anhydrous liquid HF at 250 K using platinum-iridium electrodes sealed with fluorspar caps in a platinum U-tube. In this reaction, the actual electrolyte is KF while HF acts as an ionising solvent, F₂ is evolved at the anode and H, at the cathode as indicated below:

$$\mathrm{KF} \leftrightarrow \mathrm{K}^{+} + \mathrm{F}^{-}$$

At the anode:

$$\mathrm{F}^{-} \rightarrow \mathrm{F} + \mathrm{e}$$ $$\mathrm{F} + \mathrm{F} \rightarrow \mathrm{F}_{2}$$

At the cathode:

$$\mathrm{K}^{+} + \mathrm{e} \rightarrow \mathrm{K}$$ $$2\mathrm{K} + 2\mathrm{HF} \rightarrow 2\mathrm{KF} + \mathrm{H}_{2}\uparrow$$

Potassium fluoride thus formed again undergoes electrolysis. As the hydrogen fluoride is used up, more is added to prevent the melting point of the mixture from rising. The outgoing gases, F₂ and H₂, are not allowed to mix up in the electrolytic cell. The fluorine gas is collected in plastic receivers.

Moisson's original method has been modified. In place of the expensive Pr/Ir alloy, cells made of copper, steel or Monel metal, which is a nickel-copper alloy, have been used. These get covered by a thin protective film of the fluoride just as aluminium is protected by the thin film &oxide. Anode is a carbon rod impregnated with copper to render it inert and cathode is made of steel or copper. A mixture of KF and HF in the molar ratio of 1 : 1 or 1 : 2 is used as electrolyte giving a working temperature of 515 K or 345 K, respectively.

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