(a) Suppose that an alkaline battery was manufactured using cadmium metal rather than zinc. What effect would this have on the cell emf?

Verified step by step guidance

Identify the role of zinc in a typical alkaline battery, which acts as the anode where oxidation occurs, contributing to the overall cell potential.

Understand that cadmium, like zinc, can also act as an anode in electrochemical cells, but it has a different standard reduction potential.

Look up the standard reduction potentials for both zinc (Zn) and cadmium (Cd) from a standard reduction potential table. Zinc has a standard reduction potential of -0.76 V, while cadmium has a standard reduction potential of -0.40 V.

Calculate the cell emf for both scenarios: the original battery with zinc and the hypothetical battery with cadmium, using the formula: \( E_{cell} = E_{cathode} - E_{anode} \).

Compare the calculated cell emfs to determine the effect of substituting cadmium for zinc on the cell emf, noting that a higher reduction potential for cadmium would result in a lower cell emf compared to zinc.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrochemical Cells

Electrochemical cells convert chemical energy into electrical energy through redox reactions. In these cells, oxidation occurs at the anode and reduction at the cathode. The cell emf (electromotive force) is determined by the difference in potential between these two electrodes, which is influenced by the materials used.

Standard Electrode Potentials

Standard electrode potentials are measured values that indicate the tendency of a species to be reduced, expressed in volts. Each metal has a specific standard reduction potential, which affects the overall cell potential when combined in an electrochemical cell. The choice of metals, such as cadmium versus zinc, directly impacts the cell's emf.

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products at non-standard conditions. It allows for the calculation of the emf under varying conditions, taking into account temperature and concentration changes. This equation is crucial for understanding how different materials, like cadmium and zinc, will affect the overall voltage of the battery.

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The Nernst Equation

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Textbook Question

Heart pacemakers are often powered by lithium–silver chromate 'button' batteries. The overall cell reaction is 2 Li(s) + Ag₂CrO₄(s) → Li₂CrO₄(s) + 2 Ag(s) (a) Lithium metal is the reactant at one of the electrodes of the battery. Is it the anode or the cathode?

Textbook Question

Heart pacemakers are often powered by lithium–silver chromate 'button' batteries. The overall cell reaction is 2 Li(s) + Ag₂CrO₄(s) → Li₂CrO₄(s) + 2 Ag(s) (b) Choose the two half-reactions from Appendix E that most closely approximate the reactions that occur in the battery. What standard emf would be generated by a voltaic cell based on these half-reactions?

Textbook Question

In some applications nickel–cadmium batteries have been replaced by nickel–zinc batteries. The overall cell reaction for this relatively new battery is: 2 H₂O(l) + 2 NiO(OH)(s) + Zn(s) → 2 Ni(OH)₂(s) + Zn(OH)₂(s) (c) A single nickel–cadmium cell has a voltage of 1.30 V. Based on the difference in the standard reduction potentials of Cd²⁺ and Zn²⁺, what voltage would you estimate a nickel–zinc battery will produce? (d) Would you expect the specific energy density of a nickel–zinc battery to be higher or lower than that of a nickel–cadmium battery?