The Differences Between Voltaic & Electrolytic Cells

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  • 0:03 Voltaic Cells
  • 2:34 Electrolytic Cells
  • 3:47 Similarities & Differences
  • 5:14 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

Voltaic and electrolytic cells are very similar, but there are some key differences. In this lesson, learn about both of these electrochemical cells and their importance to everyday life.

Voltaic Cells

Are you reading these words on a phone or tablet right now? Many modern technologies, including phones, tablets, and even many cars, are powered by batteries.

Although we rely on batteries every day, most of us rarely stop to think about what is actually happening inside the battery to produce the electricity that we depend on. If you looked inside a battery, you would find a series of voltaic cells, which use a chemical reaction to produce electrical energy.

Voltaic cells are named after their inventor, Alessandro Volta. Volta's original batteries, which he called voltaic piles, were made of several discs of copper and zinc placed near each other in a salty solution that we now call an electrolyte because it can conduct electricity. Each pair of copper and zinc discs is an individual voltaic cell and each cell can produce a voltage of about 0.76 V.

Volta invented the voltaic pile, which was a series of copper and zinc discs with an electrolyte solution between them.
voltaic pile

You may be wondering how exactly do these strips of copper and zinc produce electricity? It all has to do with chemistry! At the surface of the zinc, the metal undergoes an oxidation reaction, and slowly dissolves into the electrolyte as Zn2+ ions. Meanwhile, a reduction reaction is happening at the surface of the copper, and Cu2+ ions are being deposited on the surface of the copper. Here is the equation:

Oxidation-reduction reaction: Zn+Cu2+ -> Zn2+ + Cu

The result of this reaction is that the zinc progressively becomes more negatively charged as electrons are left behind at the surface, and the copper becomes positively charged as electrons are bound to copper ions. Because the zinc is the site of oxidation, it is called the anode, and the copper, which is undergoing reduction, is called the cathode. This separation of charges creates a difference in electrical potential between the two metals. Put several of these voltaic cells together and you have a battery!

In a voltaic cell, Zinc ions dissolve at the anode, and copper ions precipitate onto the cathode. As you can see in the diagram on screen, if you connect a wire to both electrodes, electrons will move from the anode to the cathode, creating an electric current.
diagram of a voltaic cell

Although not all modern batteries use copper and zinc, they still utilize voltaic cells in which oxidation-reduction reactions between two different metals generate an electric potential difference. A series of voltaic cells is what powers your phone, lights up a flashlight, and starts your car every day!

Electrolytic Cells

Now that we know what a voltaic cell is, let's look at something that is really similar, an electrolytic cell, which has a long history. An electrolytic cell converts electrical energy into chemical energy, so it operates like a voltaic cell in reverse. An input of electricity provides enough energy to reverse an oxidation-reduction reaction. Just like a voltaic cell, an electrolytic cell always contains three important parts: a cathode, an anode, and an electrolyte.

Electrolytic cells use electricity to decompose chemically bonded molecules, a process called electrolysis. For example, an electrolytic cell can decompose in water into its constituent molecules: hydrogen and oxygen.

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