What is the primary difference between the movement of charge in the external circuit versus the electrolyte?

In the external circuit, charge is carried by the flow of electrons through metallic wires. In the electrolyte, charge is carried by the physical migration of mobile ions toward the electrodes.

How does the product at the cathode in molten electrolysis differ from that in aqueous electrolysis for a reactive metal salt?

In molten electrolysis, the metal cation is the only species available to be reduced, so the metal is always produced. In aqueous electrolysis, $H^+$ ions from water are often reduced instead of reactive metal cations, producing hydrogen gas.

What is the difference between the Anode and the Cathode in terms of redox processes?

The Anode is the site of oxidation, where anions lose electrons. The Cathode is the site of reduction, where cations gain electrons.

Why is it a mistake to use the state symbol (aq) when writing equations for the electrolysis of molten lead(II) bromide?

The symbol (aq) stands for aqueous, meaning dissolved in water. Molten substances are pure liquids with no water present, so the correct state symbol is (l).

What error is made if a student predicts that solid sodium chloride will conduct electricity in an electrolytic cell?

The student is ignoring that ions in a solid lattice are held in fixed positions by strong electrostatic forces. Without mobility, the ions cannot carry charge to the electrodes, and no current will flow.

Why is it incorrect to write the anode product of molten potassium chloride as $Cl$?

Chlorine is a halogen and exists naturally as a diatomic molecule. The correct product is $Cl_2$, and the half-equation must be balanced as $2Cl^- \rightarrow Cl_2 + 2e^-$.

Define 'Electrolyte' in the context of molten ionic compounds.

An electrolyte is a liquid substance containing free-moving ions that allows for the conduction of electricity and subsequent chemical decomposition during electrolysis.

What is the general half-equation for the reduction of a metal cation $M^{2+}$ at the cathode?

The half-equation is $M^{2+}(l) + 2e^- \rightarrow M(l/s)$. This represents the cation gaining two electrons to become a neutral metal atom.

What does the mnemonic 'OIL RIG' stand for in electrochemistry?

It stands for 'Oxidation Is Loss, Reduction Is Gain' of electrons. This helps identify which reaction occurs at which electrode based on electron transfer.

Why is a Direct Current (DC) power supply used instead of Alternating Current (AC) in electrolysis?

DC provides a constant polarity, ensuring one electrode remains permanently positive and the other permanently negative. AC would constantly switch the roles of the electrodes, preventing the separation of products.

Library Podcasts

Courses

Referral & Rewards

2. Chemical Bonding, Application Of Chemical Reactions & Organic Chemistry

Electrolysis of Molten Ionic Compounds

Summary

Electrolysis is the process of using direct electrical current to drive a non-spontaneous chemical decomposition of an ionic compound. In the molten state, the rigid lattice of an ionic solid is broken, allowing ions to move freely toward electrodes where they undergo redox reactions to form pure elements.

1. Definition & Core Concepts

Electrolysis is a chemical technique that uses a direct current (DC) to initiate a chemical change that would not otherwise occur. It involves the movement of ions toward oppositely charged electrodes to facilitate the transfer of electrons.
An electrolyte is a substance that contains free-moving ions and can therefore conduct electricity. In this specific context, the electrolyte is an ionic compound that has been heated until it reaches a molten (liquid) state.
The electrodes are the conductive rods immersed in the electrolyte. The Anode is the positive electrode where oxidation occurs, while the Cathode is the negative electrode where reduction occurs.
Inert electrodes, typically made of graphite or platinum, are used to conduct electricity into the melt without participating in the chemical reactions themselves.

Diagram of an electrolytic cell showing a DC power source, anode, cathode, and ions migrating through a molten electrolyte.

2. Underlying Principles

The process relies on the mobility of ions. In a solid ionic lattice, ions are fixed in place by strong electrostatic forces; melting provides the thermal energy necessary to overcome these forces, allowing ions to act as charge carriers.
Migration of Ions: When the circuit is closed, the positive cations are attracted to the negative cathode, and the negative anions are attracted to the positive anode. This movement constitutes an internal electric current.
Redox Reactions: Electrolysis is a coupled redox process. At the cathode, cations gain electrons (reduction) to become neutral atoms. At the anode, anions lose electrons (oxidation) to become neutral atoms or molecules.
The Law of Conservation of Charge dictates that the number of electrons lost at the anode must exactly equal the number of electrons gained at the cathode during the process.

3. Methods & Techniques

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions