---
title: "Electrolysis: Half Equations at the Electrodes"
description: "A current through a molten ionic compound pulls it apart. Positive ions take electrons at the cathode and negative ions give them up at the anode, and each electrode gets its own half equation."
canonical: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY
source: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY.md
retrieved: 2026-11-12
---

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# Electrolysis: Half Equations at the Electrodes

A current through a molten ionic compound pulls it apart. Positive ions take electrons at the cathode and negative ions give them up at the anode, and each electrode gets its own half equation.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY

## Ready when they can

- Explains why an ionic solid does not conduct but the melt does
- Predicts the product at each electrode for a named molten metal halide using inert electrodes
- Writes both half equations with the electrons balanced
- Combines the two half equations back into the overall reaction

## Lesson: Splitting melts with electricity

Ion tests identify ions. Electrolysis changes them into products. An ionic solid does not conduct because its ions cannot move through the lattice. In a melt, ions can move and carry charge. A direct-current supply drives a reaction that would not occur on its own under these conditions. Electrons carry charge through the external wires.

*(drawing: Melting allows ions to move through the material and carry charge.)*

Positive ions (cations) move to the negative cathode and gain electrons to form metal atoms. This is reduction. Negative ions (anions) move to the positive anode and lose electrons. This is oxidation. For the molten metal halides here, assume inert electrodes. Lead bromide contains Pb2+ and Br- ions. Sodium chloride contains Na+ and Cl- ions. Halide ions form halogen molecules such as Br2 and Cl2.

**Example.** Balance atoms first, then total charge using electrons. For molten magnesium chloride, the cathode half is Mg2+ + 2e- -> Mg. Its left charge is +2 - 2 = 0, matching the right. The anode half is 2Cl- -> Cl2 + 2e-. Both sides have two chlorine atoms and charge -2. Reduction uses electrons on the left; oxidation releases them on the right.

Before adding halves, make electrons gained equal electrons lost. If needed, multiply every term in one or both halves. Each magnesium chloride half transfers two electrons, so they cancel. Adding gives Mg2+ + 2Cl- -> Mg + Cl2. The starting ions have the ratio in MgCl2, so write MgCl2 -> Mg + Cl2. MgCl2 gives the formula-unit ratio of this ionic compound, not a molecule in the melt.

**Recap.** Melt to free the ions, discharge cations at the cathode and anions at the anode, and balance each half.

*This lesson, question bank and flashcards were written for this dataset.*

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Redox: Oxidation and Reduction as Electron Transfer](https://lightmysky.com/learn/science/redox-oxidation-and-reduction-as-electron-transfer-mt_NMTikR0FTM)
- [Testing for Ions and Gases](https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt)

## Opens up

- [Electrolysis of Solutions and Getting Reactive Metals Out of Ores](https://lightmysky.com/learn/science/electrolysis-of-solutions-and-getting-reactive-metals-out-of-ores-mt_l-t_JxRR7f)
- [Standard Electrode Potentials and Predicting Redox Reactions](https://lightmysky.com/learn/science/standard-electrode-potentials-and-predicting-redox-reactions-mt_LDI10CjoAI)
- [Cells That Do Work: Batteries, Fuel Cells and Corrosion](https://lightmysky.com/learn/science/cells-that-do-work-batteries-fuel-cells-and-corrosion-mt_NQQzlecX4v)