Question

a strip of Ag was placed in a beaker containing 1.0 M AgNO3, and a strip of Co was put in a second beaker containing Co(NO3)2. The silver and cobalt electrodes were connected by a wire through an ammeter, and the two beakers were connected by a NaCl salt bridge.

1. Use E0 valuesto describe which way the electrons will flow. Show the direction of electron flow on the diagram, then label the anode and the cathode.Ag+ + e- = Ag (s) E0=0.80;

Co2++2 e- = Co (s) E0=-0.28

2. write and label the oxidation and reduction half-reactions that will be occuring if the electrons are flowing in the direction shown on your diagram. Show the final balanced equation.

3. Use the above 1/2 reaction to find the maximum total E0 valune for the entire cell.

4. Explain in detail what the sodium and chlorine ions in the salt bridge are doing and why they must do this.

5. What happens to the voltage of the cell as equilibrium is approached?

6. What voltage would have to be applied from another battery to make the cell run in reverse?

Answer 1

1.) The negative sign of E^o value of Co shows that it releases electrons more readily than hydrogen does. The positive value of E^o of Ag shows that it releases electrons less readily than hydrogen. That means over all, Co releases electrons more readily than Ag . Thus electron will flow as obvious from Co to Ag. In an galvanic cell electron flows from anode to the cathode , thus Co electrode will act as anode and Ag electrode as cathode.

2.)    Half cell reactions :

    At cathode :   Ag⁺ + e^- -----> Ag                      (reduction)

    At anode :     Co --------> Co²⁺ + 2e^-                (oxidation)

3.)   E_cell = E^o_red(cathode) - E^o_red(anode)

              = +0.80 - (-0.28)

              = 1.08 V

4.) the porpose of salt bridge in a cell is not to move electrons from the electrolyte but rather to maintain charge balance because the electrons are moving from one half cell to other . In detail, you can understand as the oxidation recation that occurs at anode generates elecctrons and positively charged ions.The electrons move through the wire leaving unbalanced positive charge in the vessel . In order to maintain neutrality, the negatively charged ions in the salt bridge will migrate into another anodic half cell.Thus to maintain the charge balance in the cell there must be a salt bridge present.

5.) At equilibrium the cell voltage becomes 0.00V.