Electrolysis

Electrolysis is the process by which a liquid conducts electricity through the movement of positive and negative ions within the liquid while undergoing chemical changes.

Electrolytes

Electrolytes are liquids that allow electricity to pass through them. Examples include salt solutions, alkalis, and dilute acids such as acidulated water.

Non-Electrolytes

Non-electrolytes are liquids that do not conduct electricity. Examples include distilled water, alcohol, liquid paraffin, and sugar solutions.

Electrolysis Process

1. Metals and hydrogen are deposited at the cathode.
2. Non-metals and oxygen are deposited at the anode.
3. The anode may dissolve into the solution during the process.

Electrolysis does not create electric charges but rather splits compounds using electricity. For example, water decomposes into oxygen and hydrogen when an electric current is passed through it. Electrolysis begins when the circuit is completed and stops immediately when the circuit is broken.

Faraday’s Laws of Electrolysis

Faraday’s First Law of Electrolysis

This law states that the mass of a substance liberated during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

Faraday’s Second Law of Electrolysis

This law states that the relative masses of substances liberated by the same quantity of electricity are proportional to their chemical equivalents.

Simple Calculations

If m is the mass of a substance deposited when a current I flows for time t, then the quantity of electricity that flows is It, and:

$$ m = ZIt $$

Where:

• Z = Electrochemical equivalent (e.c.e) of the substance
• I = Current (A)
• t = Time (s)
• m = Mass of the substance deposited (g)

Electroplating

Electroplating is the process of coating objects such as cutlery with a layer of metal like copper, silver, chromium, nickel, or gold. In this process:

• The object to be plated is used as the cathode.
• The metal used for coating serves as the anode.
• The electrolyte is a solution of a salt of the plating metal.

For example, in silver plating a spoon:

• The spoon is the cathode.
• Pure silver is the anode.
• Silver nitrate (\(AgNO_3\)) is used as the electrolyte.

In solution, silver nitrate dissociates as:

$$ AgNO_3 \rightarrow Ag^+ + NO_3^- $$

When electricity is passed through the solution, \(Ag^+\) ions migrate to the cathode (spoon), where they are discharged, forming a silver coating. The \(NO_3^-\) ions remain in solution, reacting with silver from the anode to maintain the electrolyte concentration.

The Purification of Metals

During the electrolysis of copper sulfate using copper electrodes:

• Copper is deposited at the cathode.
• The copper anode dissolves into the solution.

In the purification of copper:

• Impure copper is used as the anode.
• Pure copper is used as the cathode.

When a current is passed through the solution, copper ions from the anode dissolve and deposit onto the cathode, leaving impurities behind. This purified copper is then used in manufacturing electrical cables due to its low resistance.

The Electrolytic Preparation of Metals

Metals such as aluminum, sodium, and potassium are extracted from their molten chlorides or hydroxides through electrolysis.