Breaking Bad : Season 2 : Episode 9: “4 Days Out”
Walt’s latest prognosis does not look good, and he decides to accelerate his plans to provide for his family by cooking as much as he can in as short a time as possible. In this post, I’ll be talking about batteries.
So the methylamine is “losing its chemical potency”, eh? If Jesse had paid more attention when Walt was teaching him, he might know that methylamine solutions are fairly stable if kept away from air and sunlight.
There is a nice cooking montage in this episode, showing Allihn-type condensers in reflux operation. Walt and Jesse are also using aluminium foil for something, presumably as an easily-removed catalyst.
Having escaped certain death from dehydration, Walt had better drive extremely carefully now that the Winnebago has no brakes.
Batteries not included
Oddly enough, making a new battery out of the chemicals in the lab was the first thing I would have tried – either that, or trying to charge Walt’s phone using the generator. In any case, Walt builds a fairly functional mercury battery and lives to cook another day.
At the cathode, mercury oxide (Walt calls it mercuric oxide) is reduced to mercury with the help of electrons arriving through the external circuit:
HgO + H2O + 2e– → Hg + 2OH–
The powdered carbon from the brake pads is there to conduct electrons to the HgO molecules, as pure HgO is an insulator. Elemental mercury is also a highly poisonous liquid, and the presence of a fairly inert powder helps to stop it pooling.
At the cathode, zinc (galvanised materials are coated with zinc to prevent rusting) is oxidised to zinc oxide and generates electrons:
Zn + 2OH– → ZnO + H2O + 2e–
The water and OH– ions are supplied through the potassium hydroxide (KOH) electrolyte, which is effectively a solution of K+ and OH– in water (H2O). We therefore have two cycles – H2O and OH– through the electrolyte, and electrons through the external circuit. The overall cell reaction looks like this:
Zn + HgO → ZnO + Hg
So the reactions at the anode and cathode balance each other out, giving a continuous flow of electrons through the external circuit. We can visualise the complete reaction like this:
A typical mercury battery has an open circuit voltage of 1.35 V, and Walt made six of them for a total of 8.1 V. A standard car battery has six 2.1 V lead-acid cells for a total of 12.6 V. Is this enough for a jump start, or did our cooks just get lucky?
For background information on this topic, see the primer on redox.
Elements in the credits
|Robb Wilson King||Tungsten|
|MiChael Slovis||No such element|
|StewArt A. Lyons||Argon|
I’m not sure why Michael Slovis wasn’t assigned iodine (I), carbon (C), hydrogen (H), sulfur (S), oxygen (O) or vanadium (V).