Voltaic cells

Which is the incorrect statement about voltaic cells?

• Oxidation occurs at the cathode (positive electrode)

• Electricity is produced as the result of spontaneous exothermic chemical reactions

• Reduction occurs at the cathode (positive electrode)

• Voltaic cells are also called galvanic cells

The diagram shows a zinc-copper voltaic cell. Which statement is not correct when the cell is operating?

• The overall reaction taking place is:

  Cu2+(aq) + Zn(s) → Zn2+(aq) + Cu(s)

• The concentration of zinc ions in the zinc half-cell remains constant.

• Electrons flow from the zinc to the copper in the external circuit

• The salt-bridge allows the flow of ions between the two half-cells

Which is the conventional way to depict a cell made from a zinc half-cell connected to a copper half-cell?

• Zn2+(aq) / Zn(s) || Cu(s) / Cu2+(aq)

• Zn2+(aq) / Zn(s) || Cu2+(aq) / Cu(s)

• Zn(s) / Zn2+(aq) || Cu2+(aq) / Cu(s)

• Zn(s) / Zn2+(aq) || Cu(s) / Cu2+(aq)

Which is the correct half-equation for the reaction taking place at the cathode during the operation of a cell constructed from a zinc half-cell connected to a copper half-cell?

• Zn2+(aq) + 2e− → Zn(s)

• Cu(s) → Cu2+(aq) + 2e−

• Zn(s) → Zn2+(aq) + 2e−

• Cu2+(aq) + 2e− → Cu(s) 

Magnesium is above nickel in the activity series.

What must be true about a cell made from a nickel half-cell and a magnesium half-cell when it is operating.

• The overall reaction:

  Mg(s) + Ni2+(aq) → Ni(s) + Mg2+(aq) is spontaneous

• The electrons will flow through the external circuit from nickel to magnesium

• The half-equation for the reaction taking place at the anode is:

  Ni2+(aq) + 2e− → Ni(s)

• The concentration of Ni2+ ions in the nickel half-cell will increase

Explain the function of a salt bridge in a voltaic cell

• provides an electrical connection between the two half-cells to complete the circuit

• provides an pathway for electrons to flow to each of the half-cells

• allows ions to flow into or out of the half-cells to balance out the charges in the half-cells

• prevents the flow of the anions and cations from the salt used in the salt bridge to the two half-cells

A student carried out an experiment to determine the cell voltage (electromotive force) of several different simple voltaic cells. She obtained the following results: ( the table aside)

Deduce the cell voltage she would have obtained if she had connected the magnesium half-cell to the iron half-cell.

• 1.76

• 1.93

• 1.85

A student carried out an experiment to determine the cell voltage (electromotive force) of several different simple voltaic cells. She obtained the following results: (the table aside).

Identify the positive (cathode) and negative (anode) electrode when a zinc half-cell is connected to an iron half-cell.

• Cathode: Fe

  Anode: Zn

• Cathode: Zn

  Anode: Fe

A voltaic cell made up from an iron half-cell and a copper half-cell is operated.

What is the correct overall equation for the reaction in this cell?

• Fe2+(aq) + Cu(s)

  -> Fe(s) + Cu2+(aq)

• Fe(s) + Cu2+(aq)

  -> Fe2+(s) + Cu(s)

• Fe2+(aq) + Cu2+(aq)

  -> Fe(s) + Cu(s)

Which of the following is the strongest oxidizing agent?

• Pb²⁺

• Cu2+

• Ag⁺