Which of the following is used during the preparation of fluorine by Whytlaw- Gray method? (a) Aqueous HF (b) Molten \(\mathrm{KHF}_{2}\) (c) \(\mathrm{NH}_{4} \mathrm{~F}\) (d) Aqueous KF

The quest for industrially viable methods to prepare fluorine, the lightest member of the halogens, has led to the development of various techniques. Among them, the Whytlaw-Gray method stands out as a prominent approach. This method involves the electrolysis of molten potassium bifluoride (KHF₂). To understand the preparation of fluorine, we must delve into the electrochemical principles governing the electrolysis of KHF₂.
During the process, fluorine ions (Fl−) are released at the anode upon the application of an electric current, which leads to the generation of fluorine gas (F₂). This method is preferred over others as it results in pure fluorine without the production of unwanted byproducts like hydrofluoric acid (HF). An advantage of using molten salts is their capacity to conduct electricity and undergo chemical change without the presence of water, which can lead to side reactions and safety concerns due to the highly reactive nature of fluorine gas.

At the heart of fluorine production via the Whytlaw-Gray method is chemical electrolysis, an essential technique used for the separation of elements from their naturally occurring compounds. Chemical electrolysis involves passing an electric current through a liquid that contains ions—these can be molten salts or solutions. The current causes chemical reactions at the electrodes that split the compound into its constituents.
In the context of fluoride production, electrolysis takes place in a specially designed cell that contains molten potassium bifluoride. When the direct current passes through the molten salt, fluorine ions are attracted to the anode (positive electrode), where they give up their extra electrons and form elemental fluorine, a process known as oxidation. Meanwhile, the remaining potassium ions move toward the cathode (negative electrode), accepting electrons to form potassium metal, a process known as reduction. This separation technique is favored in the production of fluorine because it yields a high degree of purity and prevents the introduction of impure substances.

In this specific application, molten potassium bifluoride (KHF₂) plays a critical role in the generation of fluorine gas by way of the Whytlaw-Gray method. Potassium bifluoride is a compound that, when melted, dissociates into potassium ions (K⁺) and hydrogen fluoride (HF₂⁻), which further splits into fluoride ions (F⁻). This molten state is crucial as it ensures the efficient flow of electric current and the proper exchange of ions needed for electrolysis to occur.
Furthermore, the choice of potassium bifluoride over other fluorine compounds stems from its stability at high temperatures and its ability to avoid reacting with the materials typically used for electrodes. This stability is vital in preventing the corrosion of the anode and ensuring the efficient and safe production of fluorine. The use of a molten state as opposed to an aqueous solution helps avoid the formation of hydrogen gas at the anode, which could lead to explosive mixtures, highlighting its importance in industrial fluorine preparation.