Video Transcript
What equation shows the reaction at
the anode during the electrolysis of copper sulfate solution using inert
electrodes?
In this question, we need to
predict the products of the electrolysis of a copper sulfate salt solution. Electrolysis is a chemical process
in which electrical current is passed through a liquid or solution containing ions,
causing substances to decompose. The liquid or solution that
contains mobile ions and undergoes electrolysis is called the electrolyte. In this problem, the electrolyte is
a copper(II) sulfate solution, which has the chemical formula CuSO4 aqueous.
Now, let’s take a look at a basic
electrolytic cell to discover what reactions take place inside. Here we can see a power supply and
two electrodes, which will be used to run an electrical current through the salt
solution. In an electrolytic cell, the anode
is the positively charged electrode and the cathode is the negatively charged
electrode. These electrodes are made of an
inert substance, such as platinum or carbon. They help pass electrons through
the solution but do not take part in the chemical reactions.
To answer this question, we will
need to determine what reaction is taking place at the anode. The ions present in the salt
solution are the copper(II) cation and the sulfate anion. During electrolysis, electrons flow
from the anode to the cathode. The positively charged copper ions
will be attracted to the negatively charged cathode. But we can’t forget that the
aqueous salt solution also contains water, and water molecules can dissociate into
H+ and OH− ions. So, the positively charged hydrogen
ions are also attracted to the cathode. At the cathode, reduction takes
place, which refers to the gain of electrons.
To determine whether the H+ ions or
the Cu2+ ions will be reduced, we will need to use the reactivity series. We can see on the series that
copper is less reactive than hydrogen. When a metal element is less
reactive than hydrogen, it means it is a better oxidizing agent than hydrogen. So, at the cathode, each copper ion
will be reduced by accepting two electrons to form copper metal atoms.
At the anode oxidation takes place,
which is the loss of electrons. However, we need to determine if
the hydroxide ions or the sulfate ions will be oxidized at the anode. The more reactive anion will be
oxidized at the anode. We know that halide ions are quite
reactive. So, if halide ions, such as
chloride ions, are in the solution, they will be oxidized.
In general, if halide ions are not
present in the solution, then the hydroxide ions tend to be oxidized. Since sulfate ions are not halide
ions, we need to write an equation for the oxidation of hydroxide ions. When hydroxide ions are oxidized,
the products are water, oxygen gas, and electrons, as shown in the following
balanced chemical equation.
In conclusion, the equation that
shows the reaction at the anode during the electrolysis of copper sulfate solution
using inert electrodes is four OH− reacts to form two H2O plus O2 plus four
electrons.
