Electrolytic Cells
Electrochemistry
Electrochemistry is a branch of chemistry that describes and measures the relationship between electrical energy and a chemical chang…
Electrochemical reactions are vital to many processes in technology and the human body and involve the transfer of electrons from one chemical species to another. These reactions are called reduction-oxidation reactions or redox reactions.
When a species loses electrons, it undergoes oxidation, and we say that it is oxidized. When a species gains electrons, it has undergone reduction, and we say that it is reduced. In an electrochemical galvanic cell, redox reactions occur spontaneously, which generate electrical energy. However, in an electrolytic cell, electrical energy is applied, which causes the redox reactions to occur.
An electrolytic cell consists of the reaction solution called the electrolyte, which contains any chemical species that are oxidized or reduced as well as ions needed to enable electron flow. The electrolytic cell has two metal electrodes that are immersed in the electrolytic solution. An external circuit connects the two electrodes, which completes the circuit and enables us to apply voltage or current.
The applied current or voltage is what causes the electrochemical reaction to take place. The oxidation half-reaction occurs at the anode, and the reduction half-reaction occurs at the cathode. To help you differentiate between the two, remember the phrase 'red cat,' which stands for 'reduction at cathode'.
But how do we determine which electrode is which? We can use the standard reduction potential of the metal electrodes, which is a measure of the metal's tendency to lose electrons. The higher the reduction potential, the more likely it is for the metal to be reduced.
Let's say we place a silver electrode and a copper electrode in an electrolytic cell and apply current. The silver electrode has a higher reduction potential, so it is reduced and acts as the cathode. The copper electrode has a lower reduction potential, so it is oxidized and acts as the anode.
One use of electrolytic cells is to perform electroplating, which is a reaction where one metal is oxidized and then reduced onto the surface of another metal. Since the anode is the metal doing the plating, in our example of silver and copper, the silver electrode is plated with a thin layer of copper.
In this lab, you'll assemble an electrolytic cell and perform the electroplating process by plating a brass key with copper.
Electrochemical reactions are vital to many processes in technology and the human body and involve the transfer of electrons from one chemical species to another. These reactions are called reduction-oxidation reactions or redox reactions.
When a species loses electrons, it undergoes oxidation, and we say that it is oxidized. When a species gains electrons, it has undergone reduction, and we say that it is reduced. In an electrochemical galvanic cell, redox reactions occur spontaneously, which generate electrical energy. However, in an electrolytic cell, electrical energy is applied, which causes the redox reactions to occur.
An electrolytic cell consists of the reaction solution called the electrolyte, which contains any chemical species that are oxidized or reduced as well as ions needed to enable electron flow. The electrolytic cell has two metal electrodes that are immersed in the electrolytic solution. An external circuit connects the two electrodes, which completes the circuit and enables us to apply voltage or current.
The applied current or voltage is what causes the electrochemical reaction to take place. The oxidation half-reaction occurs at the anode, and the reduction half-reaction occurs at the cathode. To help you differentiate between the two, remember the phrase 'red cat,' which stands for 'reduction at cathode'.
But how do we determine which electrode is which? We can use the standard reduction potential of the metal electrodes, which is a measure of the metal's tendency to lose electrons. The higher the reduction potential, the more likely it is for the metal to be reduced.
Let's say we place a silver electrode and a copper electrode in an electrolytic cell and apply current. The silver electrode has a higher reduction potential, so it is reduced and acts as the cathode. The copper electrode has a lower reduction potential, so it is oxidized and acts as the anode.
One use of electrolytic cells is to perform electroplating, which is a reaction where one metal is oxidized and then reduced onto the surface of another metal. Since the anode is the metal doing the plating, in our example of silver and copper, the silver electrode is plated with a thin layer of copper.
In this lab, you'll assemble an electrolytic cell and perform the electroplating process by plating a brass key with copper.
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Q1: What is the difference between a galvanic cell and an electrolytic cell?
A galvanic cell uses spontaneous redox reactions to generate electrical energy, while an electrolytic cell applies electrical energy to drive nonspontaneous reactions. In a galvanic cell, chemical energy converts to electrical energy. In an electrolytic cell, an external power source supplies the energy needed to force the electrochemical reaction to occur.
Q2: How do you identify the anode and cathode in an electrolytic cell?
The cathode is where reduction occurs, and the anode is where oxidation occurs. You can remember this with the mnemonic 'Red Cat'—reduction at cathode. The electrode with the higher standard reduction potential acts as the cathode and is reduced, while the electrode with lower reduction potential acts as the anode and is oxidized.
Q3: What role does the electrolyte solution play in an electrolytic cell?
The electrolyte solution contains ions and dissolved salts that enable electron flow and ion movement between electrodes. When external voltage is applied, ions in the electrolyte are attracted to electrodes with opposite charges, facilitating the half-reactions. The electrolyte's concentration and conductivity directly affect the cell's resistance and current flow.
Q4: How does electroplating work in an electrolytic cell?
Electroplating deposits one metal onto another metal's surface using an electrolytic cell. The metal to be plated comprises the anode and is oxidized to form cations. These cations are then reduced at the cathode, forming a thin metal layer on the surface. The amount of metal plated depends on the applied current and the concentration of metal cations available.
Q5: What is the relationship between electrical current and the amount of metal plated?
Faraday's constant relates electrical current to moles of electrons transferred. Electrical charge equals current in amperes multiplied by time in seconds. Dividing this charge by Faraday's constant (96,485 coulombs per mole) yields the moles of electrons transferred. This determines how much metal cation is reduced and deposited during electroplating.
Q6: What is a redox reaction and how does it relate to electrolytic cells?
A redox reaction involves electron transfer between chemical species. Oxidation occurs when a species loses electrons, while reduction occurs when a species gains electrons. In electrolytic cells, applied electrical energy drives these redox reactions to occur. The oxidation half-reaction happens at the anode, and the reduction half-reaction occurs at the cathode.
Q7: Why does electrode material and solution concentration matter in electroplating?
The standard reduction potential of electrode materials determines which metal is oxidized or reduced first. Metals with higher reduction potentials are reduced preferentially. Higher electrolyte concentration increases solution conductivity, lowering resistance and increasing current flow, which allows more metal ions to be reduced and deposited onto the cathode surface.