Electrolytic Cells

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  • 0:04 Modulus of a Complex Number
  • 1:03 Electrolytic Cell Parts
  • 1:44 How Electrolytic Cells Work
  • 2:46 Electrolysis of Water
  • 4:18 Voltaic Cells
  • 5:04 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

You probably use electrolytic cells every day without ever thinking about it! In this lesson, learn all about electrolytic cells, how they work, and how they compare to voltaic cells.

Modulus of a Complex Number

You probably depend on rechargeable batteries every day to power things like cell phones, laptop computers, and other small electronic devices. When the battery runs down, what do you do? Plug it back in, right? Have you thought about what actually happens when you plug it in? How does it recharge?

Batteries provide electrical energy by utilizing a chemical reaction, but eventually it slows down because the reactants become used up. To recharge the battery, you need to reverse the reaction. This requires an input of electrical energy, which is why you have to plug in the battery to recharge it. While it's recharging, the battery acts as an electrolytic cell.

In an electrolytic cell, electrical energy is used to initiate an oxidation reduction reaction that wouldn't spontaneously occur. Electrolytic cells are not only used to recharge batteries, but also to separate pure metals from metallic compounds, to separate other chemical compounds (like water), and to electroplate metals. Let's look at little closer at exactly how electrolytic cells work.

Electrolytic Cell Parts

All electrolytic cells contain three main parts: two solid electrodes (known as the cathode and the anode) and a liquid electrolyte solution. The electrolyte solution conducts electricity because it contains dissolved ions that are free to move around throughout the solution. The cathode and anode in an electrolytic cell are attached to a source of electrical energy, like a battery.

In an electrolytic cell, the cathode is always negatively charged and the anode is positively charged. These two electrodes are made out of materials, such as copper, silver, and zinc, that participate in the chemical reaction. These are called active electrodes. They can also be made of chemically inert materials, like graphite, silicon, or platinum.

How Electrolytic Cells Work

So, now that we know the parts, let's think about how they all work together. What actually goes on in an electrolytic cell? First, the battery provides a source of electrical energy, pushing electrons onto the cathode and making it negatively charged. Electrons are also drawn out of the anode, making it positively charged. Once this happens, an oxidation-reduction reaction is activated. At the anode, an oxidation reaction occurs, releasing electrons that then are attracted to the positively charged anode. Meanwhile, at the cathode, a reduction reaction occurs, which uses up the electrons that are building up on the cathode.

Oxidation half of the reaction: X- --> X + e-

Reduction half of the reaction: Y+ + e- --> Y

After both of these reactions, the end result is that two ions (represented here by X- and Y-) turn into neutral atoms or molecules (X or Y). This is possible because of the electrical energy provided by the battery that moves electrons from the anode to the cathode.

Electrolysis of Water

Electrolytic cells are used for all kinds of things: electroplating metals, recharging a battery, and separating pure metals from metallic compounds. When electrolytic cells are used to separate chemical compounds, the process is known as electrolysis. This word literally means to use electricity to break something (electro = having to do with electricity and lysis = to break). A common type of electrolysis involves breaking down water to produce hydrogen and oxygen gas. To better understand what goes on inside an electrolytic cell, let's take a closer look at the electrolysis of water.

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