AP Chemistry - Electrochemistry Worksheet #5
1. Give the equation that relates the standard cell potential to the standard free energy change for a reaction.
 
2. What is the maximum amount of work, expressed in joules, that can be obtained from the discharge of a silver oxide battery if 1.00 g of Ag2O reacts? Eo for the cell reaction is 1.50 V.

          Zn(s) + 2 OH-(aq) ---->  Zn(OH)2(s) + 2 e-          (anode)
     Ag2O(s) + H2O + 2 e-  ---->   2 Ag(s) + 2 OH-(aq)  (cathode)

 The overall net cell reaction is
      Zn(s) + Ag2O(s) + H2---->  Zn(OH)2(s) + 2 Ag(s)
 

3. A watt is a unit of electrical power equal to one/joule/second. (1 watt = 1 J/s). How many hours can a calculator drawing 5 X 10-4 W be operated by a mercury  battery having a cell potential equal to 1.34 V if a mass of 1.00 g of HgO is available as the cathode?

           Zn(s) + 2 OH-(aq) ---->  Zn(OH)2(s) + 2 e-          (anode)
     HgO(s) + H2O + 2 e- ---->  Hg(l) + 2 OH-(aq)          (cathode)

The net reaction is

        Zn(s) + HgO(s) ----> ZnO(s) + Hg(l)
 

4. Given these half-reactions and their standard reduction potentials,

             2 ClO4- + 12 H+ + 10 e- ---->  Cl2 + 6 H2O        EoClO4- = 1.47 V

                             S2O82- + 2 e- ---->  2 SO42-                 EoS2O82- = 2.01 V

Calculate 
(a)   Eocell
(b)   ΔGo for the cell reaction, and 
(c)   the value of Kc for the cell reaction.
 

5. Calculate Kc for the system, Ni2+ + Co ---->  Ni + Co2+    Assume T=298 K.
 

6. The system 2 AgI + Sn ---->  Sn2+ + 2 Ag + I-    has a calculated Eocell = -0.015 V.  What is the value of Kc for this system?
 
7. The calculated standard cell potential for the reaction 

           Cu2+(aq) + 2 Ag(s) ---->  Cu(s) + 2 Ag+(aq)

is Eocell = -0.46 V.  Calculate Kc for this reaction.  Would you expect a relatively large amount of product to form?
 

8. Calculate ΔGo for the following reaction, given that its standard cell potential is 0.320 V at 25oC.

         NiO2 + 2 Cl- + 4 H+ ---> Cl2  + Ni2+ + 2 H2O
 

9. To chemically remove the tarnish generated by the reaction of silver with sulphide compounds, the object can be immersed in a solution of a few grams of table salt (sodium chloride) and baking soda (sodium bicarbonate) in a litre of water contained in an aluminum pan.  The sulphide tarnish slowly dissolves in the solution producing Ag1+ ions and S2- ions.  Aluminum metal from the container replaces the silver ions in solution which then plate back out onto the silver object as neutral silver atoms.
Given: 

               3 Ag+(aq) + Al(s) ---->  2 Ag(s) + Al3+(aq)      Eo = +2.47 V
             Al3+(aq) + 3 e-(aq) ---->  Al                                Eo = -1.67 V

a) Write a balanced half-cell reaction for the reduction of silver ions and calculate its standard reduction potential.

b) Calculate ΔGo for the overall reaction at 25oC.

c) Calculate the cell potential at 25oC if the concentration of Al3+ and Ag+ ions are each 0.01 M.
 

10.  Calculate Kc for the following reaction.

       NiO2 + 2 Cl- + 4 H+ --->  Cl2 + Ni2+ + 2 H2O