Video: EC17-18-S1-Q40



Video Transcript

A galvanic cell whose potential is 0.34 volts is formed of a copper electrode and standard hydrogen electrode. The cell diagram of the galvanic cell is as shown. Calculate the oxidation potential of copper.

Firstly, a galvanic cell is an electrochemical cell which is spontaneous where electricity is generated. This is what the standard hydrogen electrode might look like. Hydrogen, at a pressure of one atmosphere, is applied to a platinum electrode. The platinum electrode is said to be platinised, meaning that it is coated with a very fine powder of platinum that turns it black and vastly increases its surface area. The platinum electrode sits in a bath of one-molar hydrochloric acid. And this is what the copper end of the electrochemical cell might look like, a copper plate in a bath of one-molar copper ions, likely copper sulfate.

The one thing that completes the circuit besides the external voltmeter that connects the electrodes is the salt bridge. This will be saturated by a salt, perhaps potassium nitrate. So we now have a diagram of this galvanic cell where we have a copper electrode and a standard hydrogen electrode. We have the cell potential. And what we’re looking to calculate is the oxidation potential of the copper half cell. The reaction for the oxidation of copper is copper reacts to form copper two plus plus two electrons.

Cell diagrams are written left-to-right with the anode on the left and the cathode on the right. The anode is where oxidation occurs, whereas the cathode is where reduction occurs. In this galvanic cell, the anode is the standard hydrogen electrode. Therefore, we expect the oxidation of hydrogen to occur here. H₂ reacts to form 2H⁺ plus 2e⁻. Meanwhile, at the cathode, the opposite of the oxidation potential of copper is happening. Copper two plus ions are recombining with electrons. They are being reduced to copper.

To calculate a cell potential, the oxidation of the cathode is taken away from the oxidation potential of the anode. In this case, we are taking away the oxidation potential of copper from the oxidation potential of hydrogen. And it is the oxidation potential of copper that we want to calculate. Meanwhile, the oxidation potential of hydrogen in the standard hydrogen electrode is defined at zero volts.

This is the purpose of the standard hydrogen electrode to serve as a zero point for all other electrode potentials. We can substitute in from the question 0.3 volts as the cell potential and zero volts as the oxidation potential of hydrogen. By rearranging the equation, we’ve proved that the oxidation potential of copper is negative 0.34 volts.

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