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Chemistry LibreTexts

Homework 2: Electrochemistry

These homework problems are suggested and will not be turned in for review. However, answers will be available for them the following week by your class TAs. For more homework feel free to go to the Homework page.

True/False

  1. Platinum cannot be plated from solution by electrolysis.
  2. Reactions which are readily reversed by a small change in  concentration are ones in which E is close to zero. 
  3. All solutions of electrolytes conduct electricity.
  4. Electrolysis can only be performed on solutions.
  5. In electrolysis, the process occurring at the cathode is oxidation.  
  6. In any cell, electrolytic or voltaic, the cathode is the negative  electrode. 
  7. An anode is a positive electrode.  
  8. The liberation of free elements from liquids by the passage of an  electric current is called neutralization.  
  9. Electrolysis can be carried out in molten salts as well as in water solutions. 
  10. Electroplating is the reverse of electrolysis.

Q9

Consider the cell: Ag(s) | Ag+(1.0M) || Cu2+(1.0M) | Cu(s)

  1. Write the chemical reaction that takes place in this cell. In which direction will the reaction proceed spontaneously?
  2. What is Eo for the cell?
  3. Do electrons floow from Ag to Cu in the external circuit, or the other way?

Q10

Consider the following cell: Ni | Ni2+(0.010M) || Sn2+(1.0M) | Sn

  1. Predict the direction in which spontaneous reactions will occur.
  2. Which metal, Ni or Sn, will be the cathode and which the anode?
  3. What is Eo for the cell?
  4. What will E be for the cell with the specified concentrations at 25°C?

Q11

Consider the cell: Sn | SnCl2 (0.10M) || AgCl(s) || Ag

  1. Will electrons flow spontaneously from Sn to Ag, or in the reverse direction?
  2. What is the standard potential, Eo, for the cell?
  3. What will the cell potential, E, be at 25°C?

Q12

Use the line notation of the previous problems to represent a cell that uses the following half-reactions:

PbO2 + 4H+ + 2e- → Pb2+ + 2H2O
PbSO4 + 2e-  →  Pb + SO42-

  1. Which is the reaction at the cathode of the cell? Which way do electrons flow in an external circuit?
  2. What is Eo for this cell?

Q14

Find the missing standard reduction potentials for these following half-reactions:

Half-reaction Eo (V)
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O + 1.49
Au3+ + 3e- → Au(s) + 1.42
Cl2 + 2e- → 2Cl- ?
AuCl4- + 3e- → Au(s) + 4Cl- ?
4H+ + NO3- + 3e- → NO + 2H2O ?

lf we assume that all reactants and products are at unit activity:

  1. Which substance in the half-reactions given is the best oxidizing agent? Which is the best reducing agent?
  2. Will permanganate oxidize metallic gold?
  3. Will metallic gold reduce nitric acid?
  4. Will nitric acid oxidize metallic gold in the presence of Cl- ion?
  5. Will metallic gold reduce pure Cl2 gas in the presence of water?
  6. Will chlorine oxidize metallic gold if Cl- ion is present?
  7. Will permanganate oxidize chloride ions?

Q15

Find the standard reduction potentials for the following half-reactions;

SO42- + 4H+ + 2e- → H2SO3 + H2O
Ag+ + e- → Ag

  1. Write the balanced overall reaction for a successful cell made from these two couples,
  2. Write the line notation for the cell. 
  3. What is E° for the cell?
  4. What is the equilibrium constant for the cell reaction at 25°C?
  5. Calculate the ratio of activities of products and reactants, Q, that will produce a cell voltage of 0.51 V.