Question Video: Calculating the Standard Reduction Potential of an Electrode | Nagwa Question Video: Calculating the Standard Reduction Potential of an Electrode | Nagwa

# Question Video: Calculating the Standard Reduction Potential of an Electrode Chemistry • Third Year of Secondary School

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The standard cell potential for the galvanic cell Zn(s) | Zn²⁺(aq, 1 M) || Cu²⁺(aq, 1 M) | Cu(s) is 1.10 V. If the standard reduction potential of Cu²⁺(aq) + 2e⁻ ⟶ Cu(s) is 0.34 V, then determine the standard reduction potential of Zn²⁺(aq) + 2e⁻ ⟶ Zn(s).

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### Video Transcript

The standard cell potential for the galvanic cell Zn solid, Zn2+ aqueous one molar, Cu2+ aqueous one molar, Cu solid is 1.10 volts. If the standard reduction potential of Cu2+ aqueous plus two electrons reacts to form Cu solid is 0.34 volts, then determine the standard reduction potential of Zn2+ aqueous plus two electrons reacts to form Zn solid.

In this question, we want to know the standard reduction potential, also known as the standard electrode potential, of one of the half-cells in a galvanic cell. A galvanic cell is made up of two half-cells, an anode and a cathode. The anode is the site of oxidation, while reduction occurs at the cathode. So overall, a redox reaction occurs in a galvanic cell.

We are told the standard potential of the cell is 1.10 volts. Standard cell potential is given the symbol 𝐸 cell with a superscript ⦵ sign. The ⦵ sign indicates standard conditions, which are one atmosphere pressure, 25 degrees Celsius, and one molar electrolyte concentrations. And we are given the standard reduction potential of one of the electrodes, the copper electrode, which is 0.34 volts. We need to find the standard reduction potential of the zinc electrode.

The standard reduction potential is thought of as the difference in the electrical potential between a half-cell and the standard hydrogen electrode. It is the potential of an electrode to be reduced relative to the potential of the standard hydrogen electrode, whose potential is given to be 0.00 volts.

Using this equation, we can calculate the unknown value. The standard cell potential, 𝐸 cell, is equal to the standard reduction potential of the cathode minus the standard reduction potential of the anode.

But which electrode is the cathode and which is the anode? Cell notation is always written with the anode information first and the cathode information second. So we know that copper is the cathode, and copper ions are reduced to copper metal in this half-cell. And zinc metal is oxidized to zinc two plus ions.

Now we can substitute the potential values given to us: 1.10 volts for 𝐸 cell and 0.34 volts for 𝐸 cathode, since copper is the cathode. Rearranging, we get 0.34 volts minus 1.10 volts. This gives a value for 𝐸 anode of negative 0.76 volts, which is the standard reduction potential of the zinc electrode. It makes sense that zinc should have a smaller or more negative standard reduction potential than copper, since the smaller the standard reduction potential is, the less likely that substance is to be reduced, and the more likely it is to be oxidized.

We know from the cell notation that zinc is the anode where oxidation occurs. So it makes sense that we should end up with a value smaller and more negative than copper’s value. And we should recognize that this value indicates the potential for zinc ions to be reduced to zinc metal. But in reality, zinc metal is oxidized to zinc ions.

Finally, we have determined that the standard reduction potential for the zinc half reaction is negative 0.76 volts.

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