Question

How is fluorine isolated from fluorides?

Answer 1

Dennis method: In this, fluorine is prepared by the electrolysis of fused sodium or potassium hydrogen fluoride(perfectly dry). Electrolysis is carried out between graphite electrodes in a V-shaped electrically heated copper tube. The ends of the tube are covered with copper caps into which the graphite electrodes are fixed with bakelite cement. The copper tube is thickly lagged to prevent loss of heat.
Preparation of fluorine:
$KH{F}_2\to KF+HF$
$HF\to H^{+}+F^{-}$
At cathode
$2H^{-}+2e^{-}\to H_2$
At anode
$2F^{-}2e^{-}\to F_2$
Fluorine liberated at the anode is passed through the U-tube containing sodium fluoride. This removes the hydrogen fluoride vapours coming with fluorine.
$NaF+HF\to NaH{F}_2$.