Question

2. Answer the following questions having to do with voltaic and electrolytic cells.

A) Use the standard reduction potentials below to write the cell reaction the would produce the greatest potential in a voltaic cell.

B) Cd^2+ (aq) + 2e- -> Cd (s) E = -.402 V

Tl+ (aq) + e- -> Tl (s)   E = -.336 V

Cu^2+ (aq) + e- -> Cu+ (aq) E = +.161 V

B1) For the galvanic cell based on the reaction above, calculate the cell potential and list three different ways of changing the cell potential.

B2) For each of the changes listed in B1) state whether it will cause the potential to increase or decrease relative to the value of E and account for these effects.

C) List three factors the influence the mass of metals that can be deposited for a 1 M aqueous solution of its ions. For each of these factors state how it ill affect the mass of metal deposited. Justify your answer.

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Answer 1

At Cathode: 2x(Cu^2+ (aq) + e- -> Cu+ (aq) )   E = 2x(+.161 V )= 0.322 V

At Anode: Cd^2+ (aq) + 2e- -> Cd (s) E = -.402 V

Cell potential= E_red,cathode - E_red,anode
                   = 0.322 - (-.402)
                   = 0.724 Volts

This is the maximum possible potential

B2) According to the Nernst Equation,

E=E°−(RT/nF)lnQ

The temperature term in this equation shows that temperature affects the cell voltage. Increasing the temperature decreases the cell potential if Q>1.

For an equilibrium reaction such as A⇌B + C,

Q=[B][C]/[A]

The concentration terms in this equation shows that concentration affects the cell voltage. Increasing the concentration of products decreases the potential while increasing the concentration of reactants increases the potential.

The magnitude of electrode potential also depends on the nature of the electrodes. Electrodes with greater standard reduction potential give greater cell potential.

C) Factors Effecting the mass of metals that can be deposited
1. Temperature: Increasing the temperature will increase the amount of metal deposited
2. Current density: Increasing the current density will increase the amount of metal deposited
3. Time: Increasing the time for which current is passed through the solution will increase the amount of metal deposited