Video Transcript
Copper metal is deposited at the
cathode during the electrolysis of molten copper(II) chloride, CuCl2, liquid. What substance is produced at the
cathode during the electrolysis of aqueous copper(II) chloride? (A) Oxygen gas, (B) hydrogen gas,
(C) copper metal, (D) steam, (E) chlorine gas.
Our question asks us to determine
the product of an electrolysis reaction involving aqueous copper(II) chloride. We can answer this question using
our knowledge of the reactivity series and the electrolysis of salt solutions as
opposed to the electrolysis of molten solutions. The reactivity series is a ranking
of common metals based upon their reactivity. In a typical reactivity series
containing metal elements, we often find hydrogen, a nonmetal, that is used as a
reference element to better understand the reactivity of the metals. Typically, metals that are above
hydrogen in the series are highly reactive, while metals below hydrogen are quite
unreactive.
We can use this information to help
determine which products will form at the cathode of an electrolysis reaction of a
salt solution. In a reactivity series, any metal
that is above hydrogen, meaning it is more reactive, will produce hydrogen gas at
the cathode of a reaction when the electrolyte is an aqueous solution. Any element below hydrogen will
instead produce the pure elemental form of the metal at the cathode.
Our question tells us that the
product that forms at the cathode from electrolysis reaction of a molten salt
solution of copper(II) chloride is pure elemental copper. This is unsurprising as in a molten
solution we only have positive copper ions and no hydrogen ions supplied by the
water molecules as with an aqueous solution. In this case, the fact that we are
discussing a solution of copper chloride as opposed to the molten salt means very
little for our answer.
The important cation for both the
solution and the molten salt is copper two plus, a metal that is less reactive than
hydrogen. This cation will migrate to the
negatively charged cathode and deposit in the form of elemental copper metal. The product in both cases will be
elemental copper.
If we look at our available answer
choices, only answer choice (C) mentions copper metal. Copper metal is the correct
answer.
