Video: Electrolysis of Molten Sodium Salts

Which one of the following molten salts would not produce sodium metal when electrolyzed? [A] Na₂O [B] NaCl [C] NaBr [D] NaF [E] MgCl₂

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Video Transcript

Which one of the following molten salts would not produce sodium metal when electrolyzed? A) Na₂O, B) NaCl, C) NaBr, D) NaF, or E) MgCl₂.

Let’s imagine we have an electrochemical cell with a molten salt. In the molten salt, ions are going to be mobile. The anion is going to be attracted to the positive electrode and will be oxidized, often to form a gas. The cation, typically a metal, will be attracted to the negative electrode, where it will be reduced and form a solid metal. Since there’s the cation in any molten salt that will form a solid metal when electrolyzed, we only need to identify the cation in each substance.

Na₂O is sodium oxide. The cation is sodium plus. NaCl is sodium chloride. Again, the cation is Na⁺. The same is true for NaBr, which is sodium bromide, and NaF, sodium fluoride. However, MgCl is magnesium chloride. The cation in this case is Mg²⁺. The cations in option A, B, C, and D are all Na⁺. Upon reduction, they will all form sodium metal. The only molten salt that will not produce sodium metal is MgCl₂. The cation for MgCl₂, Mg²⁺, will be reduced to magnesium metal.

So of the five molten salts given, the only one that would not produce sodium metal when electrolyzed is MgCl₂.

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