The battery of “Breaking Bad”

Introduction

In this experiment we will reproduce the battery that is built in episode 9 of season 2 of the TV series “Breaking Bad”. The battery is a device by which it is possible to transform the chemical energy, which is released during a redox reaction, into electrical energy. Redox reactions are characterized by the transfer of electrons between an oxidizing and reducing species. The battery makes it possible to exploit the flow of electrons between two substances, one at the positive pole (cathode) which is reduced and one at the negative pole (anode) which oxidizes, generating a direct electric current, whose electric potential is a function of the oxidation and reduction reactions that take place. The transfer of electrons between the two substances can take place either by direct contact of the relevant substances, or by keeping the substance which is being oxidized separate from that which is being reduced, making sure that the electrons which are freed in the oxidation process reach, through a conductor metallic, the vessel where the reduction reaction takes place.

It is necessary to put the two containers in communication with each other by means of a salt bridge, which allows to maintain the electro neutrality of the battery and guarantees that the positive charges are equal in number to the negative ones.

In this experiment, we build 4 cells and they will be connected in series, i.e. joining the anode with the cathode so as to have a single positive pole and a single negative pole. Furthermore, with this connection the overall potential is equal to the sum of the individual cell potentials.

However, unlike the TV series, in this reproduction we will use iron oxide instead of the highly harmful mercury oxide, and the graphite will not be present as it is used by Walter only for the conductor of electricity, as the oxide of mercury is unable to do this.

 

References

Walter White, a chemistry professor, offers Jesse Pinkman, a former student of his, a four-day marathon in the New Mexico desert to cook as much methamphetamine as possible, using rudimentary tools hidden in an old camper. After two days, they realize that the vehicle won’t start again, because Jesse left the key inserted in the ignition, discharging the camper’s battery. However, after several vain attempts to restart the camper, Walter has the idea of ​​building a homemade battery with which to restart it, using objects at their disposal.

In the cell built by Walter, the anode is made up of zinc (Zn) contained in coins, bolts, washers, etc. The cathode consists of mercury oxide (HgO), and the graphite of the brake pads, which does not participate in the reaction but merely acts as an electrode. The salt bridge consists of a sponge soaked in an aqueous solution of potassium hydroxide (KOH). Finally, the metallic conductor that allows the transfer of electrons between Zn and HgO is a simple copper wire.

Cells of this type provide a potential difference of 1.35V and, since Walter builds six of them, the maximum voltage will be just over 8V.

Materials

• Four sponges;
• Four small containers;
• Une large container;
• Copper wires;
• 13,5oz becher;
• Weighting containers;
• Weighting scale;
• Stirring stick;
• Spatula;
• Cutter;
• Voltmeter;
• Distilled water;
• Potassium hydroxide (KOH);
• Iron oxyde(III) (Fe₂O₃);
• Zinc (Zn).

 

Protective equipment and chemical hazards

• Laboratory coat;
• Latex gloves;
• Protection goggles.

 

  

 

 

 

Corrosive (KOH)           Harmful irritant(KOH)                          

 

Procedure

First of all, the structure of the pile is prepared, inserting the four smaller ones in the larger bowl.

Then the salt bridge is prepared: a 1 M solution of potassium hydroxide and distilled water. First, 0.2 mol of KOH, or 11.22 g, is weighed into the boat and 200 mL of distilled water is poured into the beaker; therefore, sodium hydroxide is added and everything is mixed with a rod to obtain a homogeneous solution.

Next, you need to weigh out the amount of iron oxide needed to build the pile. As happened with KOH, 10.3 g of Fe2O3 are weighed with the spatula in a boat. Since the pile you are building is made up of four cells, this procedure must be performed four times.

Now you can build the actual stack. The sponges are soaked in the KOH solution and placed in the center of each single small basin; then, with a scalpel, two furrows are created in each sponge, in which we will place the zinc foils and the iron oxide. Therefore, in each sponge, zinc sheets wrapped in a copper wire and iron oxide are placed and an additional copper wire is inserted into the groove of the iron oxide. Before concluding the experiment, the potential of each individual cell is measured with a voltmeter.

Finally, the cells are arranged in series by connecting the copper wires together and the potential of the complete battery is measured using the voltmeter.

Battery chemical reactions

Anode (-): Zn + 2OH^–→ ZnO + H₂O + 2e^–          

Cathode(+): Fe₂O₃ + H₂O + 3e^– → 2Fe + 2OH^– + O₂                                           

General reaction: 3Zn + 2Fe₂O₃ + 2OH^– → 3ZnO + 4Fe + 2O₂

Salt bridge: KOH → K⁺ + OH^–

 

Results

The battery built works and produces a total of about 12V and each single cell produces an average of 5.5V, which does not amount to the sum of the voltage of the individual cells probably because over time the electrical conductivity of zinc and copper has decreased.