Half equations: electrolysis
Lesson details
Learning outcome
I can write half–equations and balanced ionic equations.
Key learning points
- A half–equation describes what happens to one reactant in a reaction, such as the process at an individual electrode.
- Half–equations show balanced charges as well as balanced atoms.
- A balanced ionic equation shows all reacting ions involved in a reaction.
- Ions not involved in a reaction do not appear in a balanced ionic equation.
Keywords
Reduction - a type of reaction in which a substance gains electrons or loses oxygen
Oxidation - a type of reaction in which a substance loses electrons or gains oxygen
Half–equation - a chemical equation used to show the electrons lost in oxidation or the electrons gained in reduction
Ionic equation - a balanced equation showing all the ions involved in a reaction
Spectator ions - the ions not involved in a chemical reaction
Common misconception
Getting the electrons confused; how many and which side of the half equations to write them on.
When writing a half equation, electrons should be added and not taken away and so should go on the side of the equation where they are added. All charges must cancel each other out and the atoms on each side of the equation balance.
Teacher tip
Pupils need plenty of practice and many scaffolded examples to help.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is a chemical reaction?
Q2.What are reactants?
Q3.What are products?
Q4.What is a word equation?
Q5.What does the conservation of mass mean?
Q6.What is a chemical symbol?
Assessment exit quiz
6 Questions
Q1.What does a half-equation describe?
Q2.What do half-equations show?
Q3.When an atom gains electrons we say it has been ...
Q4.In an electrolysis cell, where does oxidation occur? why?
Q5.What are spectator ions?
Q6.In the electrolysis of molten zinc chloride, the ionic equation is Zn²⁺(l) + 2Cl⁻(l) → Zn(s) + Cl₂(g). Which of the following is correct?
To help you plan your 11 chemistry lesson on: Half equations: electrolysis, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 11 chemistry lesson on: Half equations: electrolysis, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 chemistry lessons from the Electrolysis unit, dive into the full secondary chemistry curriculum, or learn more about lesson planning.