Read the article and fill the gaps with appropriate words.

FLUORINE[5]
 

obtained
oxidized varies based forms
entails required steel cell stored melts
electrolysed layer conductivity improvements  


Industrial production of fluorine in the middle temperature process 1............................ the electrolysis of a solution of potassium bifluoride in hydrogen fluoride. Hydrogen fluoride 2............................ for the electrolysis is mainly 3............................ by treatment of fluorite with sulphuric acid. Several thousand tonnes of fluorine are produced annually. Potassium bifluoride 4............................ spontaneously from potassium fluoride and the hydrogen fluoride:

HF + KF KHF2

The mixture with the approximate composition KFo2HF 5............................ at 70oC and is 6............................ in the temperature range between 70 and 130oC. KHF2 increases the electrical 7............................ of the solution and provides the anion that is 8............................ at the anode, while hydrogen forms at the cathode. These electrolytes and method are 9............................ on the pioneering studies by Moissan. Since then 10............................ have been made in electrodes and containment: while Moissan used platinum group metal electrodes and carved fluorite containers, the modern process uses the 11............................ itself as cathode, while blocks of carbon are used as anode (the Söderberg carbon electrodes are similar to those used in the electrolysis of aluminium). The voltage for the electrolysis 12............................ between 8 and 12 Volts. If the fluorine gas is cleaned of hydrogen fluoride and oxygen impurities, it may be 13............................ in steel cylinders, where the inside surface becomes coated (passivated) with a metal fluoride 14............................ that resists further attack.