Chemistry: Electrochemistry: Galvanic and Electrolytic Cells Worksheet

Question 1

A galvanic cell is made from Zn and Cu electrodes. The half-reactions are Zn2+ + 2e- -> Zn with E° = -0.76 V and Cu2+ + 2e- -> Cu with E° = +0.34 V. Identify the anode, the cathode, and the direction of electron flow.

Accepted Answer

The zinc electrode is the anode because zinc is oxidized. The copper electrode is the cathode because copper ions are reduced. Electrons flow through the wire from the zinc anode to the copper cathode.

Question 2

Using the Zn and Cu standard reduction potentials, calculate the standard cell potential for the cell Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s).

Accepted Answer

The standard cell potential is E°cell = E°cathode - E°anode = +0.34 V - (-0.76 V) = +1.10 V. The positive value shows that the reaction is spontaneous under standard conditions.

Question 3

Write the balanced overall reaction for the galvanic cell Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s).

Accepted Answer

The oxidation half-reaction is Zn(s) -> Zn2+(aq) + 2e-. The reduction half-reaction is Cu2+(aq) + 2e- -> Cu(s). The balanced overall reaction is Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s).

Question 4

Explain the purpose of the salt bridge in a galvanic cell.

Accepted Answer

The salt bridge allows ions to move between the half-cells so that charge does not build up. This keeps the circuit complete and allows the redox reaction to continue.

Question 5

A student builds a cell with Fe and Ag electrodes. The standard reduction potentials are Fe2+ + 2e- -> Fe with E° = -0.44 V and Ag+ + e- -> Ag with E° = +0.80 V. Identify which substance is oxidized and which ion is reduced.

Accepted Answer

Iron metal is oxidized to Fe2+ because it has the lower reduction potential. Silver ions are reduced to silver metal because Ag+ has the higher reduction potential.

Question 6

For the Fe and Ag cell in problem 5, write the balanced overall reaction and calculate E°cell.

Accepted Answer

The balanced overall reaction is Fe(s) + 2Ag+(aq) -> Fe2+(aq) + 2Ag(s). The standard cell potential is E°cell = +0.80 V - (-0.44 V) = +1.24 V.

Question 7

Classify each cell as galvanic or electrolytic: Cell A produces electrical energy from a spontaneous redox reaction. Cell B uses a battery to force a nonspontaneous redox reaction.

Accepted Answer

Cell A is a galvanic cell because it converts chemical energy from a spontaneous reaction into electrical energy. Cell B is an electrolytic cell because it uses electrical energy to drive a nonspontaneous reaction.

Question 8

In an electrolytic cell containing molten sodium chloride, Na+ ions move toward one electrode and Cl- ions move toward the other. Identify what happens at the cathode and at the anode.

Accepted Answer

At the cathode, Na+ ions gain electrons and are reduced to sodium metal. At the anode, chloride ions lose electrons and are oxidized to chlorine gas.

Question 9

Compare the signs of the electrodes in galvanic and electrolytic cells.

Accepted Answer

In a galvanic cell, the anode is negative and the cathode is positive because electrons are produced at the anode and flow to the cathode. In an electrolytic cell, the anode is positive and the cathode is negative because an external power source forces electron movement.

Question 10

A current of 2.00 A passes through a copper(II) sulfate solution for 20.0 minutes. Copper is plated according to Cu2+ + 2e- -> Cu. Calculate the mass of copper plated. Use F = 96,485 C/mol e- and molar mass of Cu = 63.55 g/mol.

Accepted Answer

The charge is Q = It = (2.00 A)(1200 s) = 2400 C. The moles of electrons are 2400 C divided by 96,485 C/mol, which is 0.0249 mol e-. Since 2 mol e- plate 1 mol Cu, the moles of Cu are 0.0124 mol. The mass plated is 0.0124 mol times 63.55 g/mol = 0.790 g Cu.

Question 11

A current of 5.00 A runs through molten MgCl2 for 30.0 minutes. Magnesium forms according to Mg2+ + 2e- -> Mg. Calculate the mass of magnesium produced. Use F = 96,485 C/mol e- and molar mass of Mg = 24.31 g/mol.

Accepted Answer

The charge is Q = It = (5.00 A)(1800 s) = 9000 C. The moles of electrons are 9000 C divided by 96,485 C/mol, which is 0.0933 mol e-. Since 2 mol e- produce 1 mol Mg, the moles of Mg are 0.0466 mol. The mass of magnesium is 0.0466 mol times 24.31 g/mol = 1.13 g Mg.

Question 12

A cell has E°cell = -0.50 V as written. Explain whether the reaction is spontaneous as written and describe one way to make it occur in an electrolytic cell.

Accepted Answer

The reaction is not spontaneous as written because the standard cell potential is negative. To make it occur in an electrolytic cell, an external power source with enough voltage can be connected to force the reaction to proceed.

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Chemistry: Electrochemistry: Galvanic and Electrolytic Cells

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