Electrolytic Cells

Why are electrolytic cells called electrolytic?

``Lytic'' comes from the root word ``to split,'' and electro, well, simply means electricity. So, electrolytic cells use electricity to split molecules, which is also known as electrolysis.

This occurs at the electrodes and can result, in the deposition of an element (electroplating) and the splitting of a molecule to release a gas.

What are electrolytes?

A substance that dissociates into free ions when dissolved in water. These ions in turn facilitate the conduction of electricity.

In organisms, replenishing electrolytes (e.g. Gatorade) is important to maintain homeostasis of key ions (Na$^{+}$, K$^{+}$).

What is the $\Delta$G of electrolytic cells?

+$\Delta$G, i.e. the reaction is $non-spontaneous$.

What is Faraday's law (aka the first law of electrolysis)?

The mass of a substance produced at an electrode during electrolysis is proportional to the number of moles of electrons transferred at that electrode.

Basically, the amount of electrical current (moles of electrons) in an electrolytic cell is directly related to how much splitting occurs. This is the basis of Faraday's constant, which is calculated by multiplying the charge of one electron with the number of electrons in one mole.

How can you relate the effect of one mole of electrons?

$$(1.6 x 10^{-19} Coulombs)(6.022 x 10^{23} e Ð /mol) = 96,487 C/mol e^{Ð}$$ (34.1)

The importance of this calculation is that a connection between moles and electrical charge is made.

How would you calculate the moles of an element that would be deposited at an electrode?

One way would be to calculate the amount of Coulombs that passes through the electrolytic cell. If the electrical charge is represented in amps, convert to Coulombs:

$$Amps = \frac{Coulombs}{seconds}$$ (34.2)

The key concept is to understand that Coulumbs are related to moles using Faraday's constant. Importantly, if you are given the amount of time that the current was applied to the system, you can calculate the numbers of moles that were deposited.

Label the various parts of the molten NaCl electrolytic cell:

Figure 33.1: The Electrolytic Cell.

1. Anode	5. Na$^{+}_{(l)}$
2. Cathode	6. Molten NaCl
3. Battery	7. Direction of e$^{-}$ flow
4. Cl $_{2 \ (g)}^{-}$