Name: Essay – Electrochemistry

1.  Under standard conditions at 25 oC, Zn(s) reacts with Co2+(aq) to produce Co(s).

  1. Write the balanced equation for the oxidation half reaction.
  2. Write the balanced net – ionic equation for the overall reaction
  3. Calculate the standard potential, Eo, for the overall reaction at 25oC.

2.  At 25oC, H2O2 decomposes according to the following equation:

2 H2O2(aq) à 2 H2O(l) + O2(g) Eo=0.55 V

  1. Determine the value of the standard free energy change, ΔGo, for the reaction at 25oC.
  2. Determine the value of the equilibrium constant, Keq, for the reaction at 25oC.
  3. The standard reduction potential, Eo, for the half reaction is shown below:

O2(g) + 4 H+(aq) + 4 e- à 2 H2O(l) Eo = 1.23 V

Using this information in addition to the information given above, determine the value of the standard reduction potential, Eo, for the reaction below:

O2(g) + 2 H+(aq) + 2e- à H2O2(aq)

3.  In an electrolytic cell, Cu(s) is produced by the electrolysis of CuSO4(aq). Calculate the maximum mass of Cu(s) that can be deposited by a direct current of 100. A passed through 5.00 L of 2.00 M CusSO4(aq) for a period of 1.00 hour.

4.  Answer the following questions that refer to the galvanic cell shown below. You will need a table of standard reduction potentials as well.

  1. Identify the anode of the cell and write the half – reaction that occurs there.
  2. Write the net ionic equation for the overall reaction that occurs as the cell operates and calculate the value of the standard cell potential, Eocell.
  3. Indicate how the value of Ecell would be affected if the concentration of Ni(NO3)2(aq) was changed from 1.0 M to 0.10M and the concentration of Zn(NO3)2(aq) remained at 1.0 M. Justify your answer.
  4. Specifiy whether the value of Keq for the cell reaction is less than, greater than or equal to1. Justify your answer.

5.  The diagram below shows the experimental setup for a typical electrochemical cell that contains two standard half – cells. The cell operates according to the reaction represented by the following equation:

Zn(s) + Ni2+(aq) à Ni(s) + Zn2+(aq)

  1. Identify M and M2+ in the diagram and specify the initial concentration of M2+ in solution.
  2. Indicate which of the metal electrodes is the cathode. Write the balanced equation for the reaction that occurs in this half – cell.
  3. What would be the effect on the cell voltage if the concentration of Zn2+ was reduced to 0.100 M in the half – cell containing the Zn electrode?
  4. Describe what would happen to the cell voltage if the salt bridge was removed. Explain.

6.  The reaction between silver ion and solid zinc is represented by the following equation:

2 Ag+(aq) + Zn(s) à Zn2+ + 2 Ag(s)

a. A 1.50 g sample of Zn is combined with 250. mL of 0.110 M AgNO3 at 25oC.

i. Identify the limiting reactant. Show calculations to support your answer.

ii. On the basis of the limiting reactant that you identified, determine the

value of [Zn2+] after the reaction is complete. Assume that volume change

is negligible.

b. Determine the value of the standard potential, Eo, for a galvanic cell based on

the reaction between AgNO3(aq) and solid Zn at 25oC.

7.  A galvanic cell based on the reaction between Ag+(aq) and Cu(s), represented by the equation below. At 25oC, the standard potential, Eo, for the cell is 0.46V.

2 Ag+(aq) + Cu(s) à Cu2+(aq) + 2 Ag(s)

a. Determine the value of the standard free – energy change, ΔGo, for the reaction

between Ag+(aq) and Cu(s) at 25oC.

b. The cell is constructed so that [Cu2+] is 0.045 M and [Ag+] is 0.010 M. Calculate the value of the potential, E, for the cell.

c. Under these conditions, is the reaction in the cell spontaneous? Justify.

8.

d. Of the compounds NaOH, CuS, and NaNO3, which one is appropriate to use in a salt bridge. Explain your answer, and for each of the other compounds, include a reason why it is not appropriate.

e. Another standard cell is based on the following reaction.

Zn + Pb2+ à Zn2+ + Pb

If the concentration of Zn2+ is decreased from 1.0 M to 0.25 M, what effect does this have on the cell potential? Justify.

9.  The following questions refer to the electrochemical cell shown below.

a.  Write a balanced net ionic equation for the spontaneous reaction that takes place in the cell.

b.  Calculate the standard cell potential, Eo, for the reaction is part (a).

c.  In the diagram above,

  1. Label the anode and the cathode on the dotted lines provided
  2. Indicate, in the boxes below the half-cells, the concentration of AgNO3 and the concentration of Zn(NO3)2 that are needed to generate Eo.

d.  How will the cell potential be affected if KI is added to the silver half-cell? Justify.

10. An electrochemical cell is constructed with an open switch, as shown in the diagram below.

A strip of Sn and a strip of an unknown metal, X, are used as electrodes. When the switch is closed, the mass of the Sn electrode increases. The half- reactions are shown below.

Sn2+(aq) + 2e- à Sn(s) Eo = -0.14 V

X3+(aq) + 3e- à X(s) Eo= ?

a.  In the diagram above, label the electrode that is the cathode. Justify

b.  In the diagram above, draw an arrow indicating the direction of the electron flow in the external circuit when the switch is closed.

c.  If the standard cell potential, Eocell, is +0.60 V, what is the standard reduction potential, in volts, for the X3+/X electrode?

d.  Identify metal X

e.  Write a balanced net – ionic equation for the overall chemical reaction occurring in the cell.

f.  In the cell, the concentration of Sn2+ is changed from 1.0 M to 0.50 M, and the concentration of X3+ is changed from 1.0 M to 0.10 M.

  1. Substitute all the appropriate values for determining the cell potential, Ecell, into the Nernst equation. (Do not do any calculations)
  2. On the basis of your response in part (f) (a), will the cell potential, Ecell, be greater than, less than, or equal to the original Eocell? Justify.

11. Answer the following questions about voltaic cells.

e.  A voltaic cell is set up using Al/Al3+ as one half – cell and Sn/Sn2+ as the other half – cell. The half – cells contain equal volumes of solutions and are at standard conditions.

  1. Write the balanced net – ionic equation for the spontaneous cell reaction.
  2. Determine the value, in volts, of the standard potential, Eo, for the spontaneous cell reaction.
  3. Calculate the value of the standard free – energy change, ΔGo, for the spontaneous cell reaction.
  4. If the cell operates until [Al3+] is 1.08 M in the Al/Al3+ half – cell, what is the [Sn2+] n the Sn/Sn2+ half cell?

f.  In another voltaic cell with Al/Al3+ as one half – cell and Sn/Sn2+ as the other half – cell, [Sn2+] is 0.010 M and [Al3+] is 1.00 M. Calculate the value, in volts, of the cell potential, Ecell, at 25oC.

12.