Video Transcript
Which of the following reactions
occurs at the anode during the electrolysis of aluminum? (A) Al3+ reacts to produce Al plus
three e−. (B) Two O2− reacts to produce O2
plus four e−. (C) Two O2− plus four e− reacts to
produce O2. (D) Al3+ plus three e− reacts to
produce Al. Or (E) O2 reacts to produce two O2−
plus four e−.
We want to know which of the given
reactions occurs at the anode during the electrolysis of aluminum. Oxidation occurs at the anode. Thus, we know that the reaction
must be an oxidation reaction. For this reason, we can eliminate
answer choices (C) and (D), which show species gaining electrons. Thus, they are reduction
equations.
If we look closely at the reaction
equations, we can see that the charges in equations (A) and (E) do not balance. Therefore, we can eliminate answer
choices (A) and (E).
We can tell by process of
elimination that answer choice (B) is correct. But let’s quickly confirm that. To do this, we can look at the ions
that would be in solution. If we look at this setup for the
extraction of aluminum, we can see that the electrolyte comes from alumina, which is
the common name for aluminum oxide. Alumina is combined with cryolite
and is melted, forming aluminum ions and oxide ions.
We also know that in electrolysis,
the anode is the positive electrode. The positive anode attracts
negative ions, which are then oxidized. As oxide ions are negative, we can
be sure that the reaction that occurs at the anode during the electrolysis of
aluminum is (B). Two O2− reacts to produce O2 plus
four e−.
