GCSE Chemistry Revision: Electrolysis notes

Introduction to Electrolysis

Electrolysis is the process of using an electric current to drive a non-spontaneous chemical reaction. It involves the use of an electrolytic cell, which consists of an electrolyte solution and two electrodes (an anode and a cathode).

Electrolyte Solutions

An electrolyte solution is a solution that contains ions. These ions are free to move and can conduct electricity. Some examples of electrolyte solutions include aqueous solutions of salts, acids, and bases.

The Anode

The anode is the positive electrode in an electrolytic cell. It attracts negatively charged ions (anions) from the electrolyte solution. At the anode, oxidation occurs, which means that electrons are lost from the anode and transferred to the anions. The anions then react with each other or with water to form products.

The Cathode

The cathode is the negative electrode in an electrolytic cell. It attracts positively charged ions (cations) from the electrolyte solution. At the cathode, reduction occurs, which means that electrons are gained by the cathode and transferred to the cations. The cations then react with each other or with water to form products.

The Electrolysis of Aqueous Solutions

When an aqueous solution is electrolyzed, the products that are formed depend on the concentration of the ions in the solution, the voltage applied to the cell, and the nature of the electrodes. The products can be predicted using a set of rules, known as the electrolysis of aqueous solutions rules.

Electrolysis of Molten Salts

When a molten salt is electrolyzed, the products that are formed depend on the nature of the salt and the electrodes. The products can be predicted using the electrolysis of molten salts rules.

Applications of Electrolysis

Electrolysis has many practical applications, such as in the production of metals, the purification of metals, the production of hydrogen and chlorine, and the electroplating of metals.

Quantitative Electrolysis

Quantitative electrolysis is the process of using an electric current to measure the amount of a substance produced or consumed during an electrolytic reaction. It involves measuring the amount of charge that passes through the cell during the reaction, and using this information to calculate the amount of product formed or consumed.

The amount of charge that passes through the cell during an electrolytic reaction is given by the formula:

Charge = Current × Time

where:

• Charge is measured in coulombs (C)
• Current is measured in amperes (A)
• Time is measured in seconds (s)

The amount of product formed or consumed during an electrolytic reaction can be calculated using Faraday's laws of electrolysis. Faraday's first law states that:

The amount of product formed or consumed during electrolysis is directly proportional to the amount of charge that passes through the cell.

Faraday's second law states that:

The amount of product formed or consumed during electrolysis is proportional to the number of moles of electrons that are transferred.

The proportionality constant in both of these laws is known as the Faraday constant, which is equal to:

1 Faraday = 96,485 C mol^-1

Using Faraday's laws, the amount of product formed or consumed can be calculated using the formula:

Amount of product = Charge / (Faraday constant × Charge on ion)

where:

• Amount of product is measured in moles (mol)
• Charge on ion is the number of electrons that are transferred per ion during the reaction