Video Transcript
The standard electrode potential, 𝐸 naught, is measured under standard
conditions. Which of the following is not a standard condition adhered to when measuring these
values? (A) Measuring against the standard hydrogen electrode. (B) Solution concentration of one molar. (C) Pressure of one atmosphere, when gases are involved. (D) Temperature of 298 Kelvin. Or (E) KNO3 solution in the salt bridge.
When a conductive electrode is placed into an electrolyte solution, a half-cell is
formed. Two half-cells can be combined to form an electrochemical cell, which is a system
that converts chemical energy to electrical energy or vice versa. When two half-cells are combined into a complete circuit, the potential difference
between the two half-cells can be measured.
However, for chemists to effectively use electrochemical cells in a scientific
manner, it is essential for the amount of potential difference between the two
half-cells to be predicted accurately. As such, the electric potential of many different half-cells have been measured under
standard conditions to provide a series of standard electrode potentials, 𝐸 naught,
where the naught symbol represents the standard conditions. And 𝐸 is the electrode potential difference between a reference electrode and an
unknown or test electrode.
Standard electrode potentials are also known as standard reduction potentials, as
they refer to the potential difference generated by the reduction reaction in the
cell. It’s important to remember that this is only half of the redox reaction possible in a
reversible electrochemical cell. As such, an oxidation reaction is complementary to the reduction reaction.
Standard reduction potential is the potential difference between an electrode and a
standard hydrogen half-cell under a set of standard conditions. This standard hydrogen electrode is also often called a reference electrode. Hydrogen reference electrodes used to measure electrode potentials at a standard set
of conditions are known as a standard hydrogen electrode.
The standard hydrogen electrode consists of a platinum or other inert metal electrode
in a glass tube with hydrogen gas bubbled at one atmosphere of pressure. The electrode is immersed in a solution containing hydrogen ions, or H+, with a
concentration of one mole per liter, at 298 kelvin. This standard hydrogen electrode is connected to the other electrode we wish to test,
or half-cell two. If we use a zinc half-cell as an example, we can see a zinc metal electrode placed
into a solution containing zinc cations. Again, the concentration used here for the zinc solution is one mole per liter.
With this information we can now assess our answer choices. Using the list of requirements for standard electrode potential conditions we have
outlined, we can see that the only answer choice we have not mentioned is the use of
potassium nitrate as the solution in the salt bridge. And while it is commonly used in electrochemical cells, it is not necessarily a part
of the experimental set up for measuring standard electrode potentials.
So we can correctly choose answer choice (E), KNO3 solution in the salt bridge, as
the correct answer.
