Fourth Lab Session - How to make a battery with redox couples

Mª Eugenia Fernández de los Ronderos, Maite Pérez Lagares and Luis Galán Ruiz

05/02/2013

Objective: To build a battery (energy emitter) with two redox couples.

Materials:

                       

     - U-tube                                      - Multimeter                                        - lead (II) nitrate

              

    - magnesium                              - magnesium sulfate (aqueous solution)                        -lead

               

- 2 beakers                                     -Sodium Chloride                                      -Water 

                                                         

                                                                          - Cotton

Background information:

Redox reactions, or oxidation-reduction reactions, primarily involve the transfer of electrons between two chemical species. 

The compound that loses electrons is said to be oxidized, the one that gains electrons is said to be reduced.

There are also specific terms that describe the specific chemial species. 

A compound that is oxidized is referred to as a reducting agent, while a compound that is reduced is referred to as the oxidizing agent. (UNIVERSITY OF NORTH CAROLINA, 2012) 

Due this phenomenom, the redox couples we use today, can generate electricity.

Procedure:

1.- Fill up the U tube with NaCl and water, and put cotton in both ends, so that the solution does not fall out.            

                                                     

2.- Pour aproximately 10 mL  of lead (II) nitrate inside of a beaker.

3.- Pour aproximately 10 mL of magnesium sulfate in the other beaker.

4.- Make sure the multimeter's cables are in the following position:

5.- Put a long piece of magnesium inside the beaker containing magnesium sulfate.

6.- Put the longest fragment of lead (Pb) inside the other beaker containing lead (II) nitrate.

7.- Pin the piece of magnesium which is inside the beaker with the black clamp of the multimeter.

8.- Pin the fragment of lead with the red clamp.

9.- Set the "U tube" upside down, so that each of the ends of the tube get into both beakers, in order to conduct electricity.

10.- Turn on the multimeter to the "2000 millivolts" function.

11.- Collect the data in your notebook.

Results and Conclusions

As we can see in the image below, the energy emitted is around 1259 mV (milli-Volts).

                                                             

The redox couples used are the following:

Pb²⁺/Pb

Its reduction potential is +1,693 V

Mg²⁺/Mg

Its reduction potential is -2,363 V

As we know electrons move from left to right, the same way we write it. lead has more tendency to reduce because its reduction potencial is higher than magnesium. (+1,693 > -2,363)

The Daniell cell will remain:

Mg/Mg²⁺// Pb²⁺/Pb

So when we have these redox couples, the Daniell cell produces:

 +1,693 + 2,363 = 4,056 V.

While the potencial difference is:

-(2,363) + 1,693 = - 0,67 V

The symbol has no importance, because what we want to know is the potential difference; and the symbol what indicates us is the direction of the electrons. So, the potential difference is 0,67 V. 

References:

University of North Carolina (2012). Redox Reactions. Taken from: 

http://www.shodor.org/unchem/advanced/redox/index.html