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Science lesson plan · 12th grade (Year 13 in England) · 45 minutes

Oxidation, reduction and half-equations

Chemical reactions, acids and bases

CCSS NGSS.HS-PS1-2England: GCSE Chemistry: Chemical changes (oxidation and reduction in terms of electrons, Higher)

Objective and success criteria

Students will: Oxidation, reduction and half-equations.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Predict the products of electrolysis; The reactivity series and displacement

Leads to: the next skill in this area.

Materials: Teacher demo or video, Indicator color chart, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 5 min

  • Quick retrieval from earlier learning (Predict the products of electrolysis; The reactivity series and displacement). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Electrolysis of molten sodium chloride: what forms at the cathode (negative electrode)? (sodium / silver / aluminium / oxygen) → sodiumPrompt: Positive ions are attracted to the negative cathode.
  2. Electrolysis of copper(II) sulfate solution: what forms at the anode (positive electrode)? (oxygen / hydrogen / chlorine / sulfur) → oxygenPrompt: Negative ions are attracted to the positive anode.
  3. Electrolysis of aluminium oxide dissolved in molten cryolite: what forms at the cathode (negative electrode)? (aluminium / silver / zinc / copper) → aluminiumPrompt: Positive ions are attracted to the negative cathode.

Hook · 5 min

  • Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
  • Share the objective: Oxidation, reduction and half-equations. Read the success criteria together.

I do: model it · 10 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: Complete the half-equation at the cathode: Cu²⁺ + ? e⁻ → Cu. How many electrons are needed?
  • Step 1: Cu²⁺ needs 2 electron(s) to become a neutral copper atom.
  • Step 2: So the answer is: 2
  • Answer: 2
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 10 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. Complete the half-equation at the cathode: Fe³⁺ + ? e⁻ → Fe. How many electrons are needed? → 3Prompt: The charges on both sides must balance.
  2. Magnesium is added to a solution containing iron ions and displaces the iron. Which species is reduced? (magnesium atoms / iron ions) → iron ionsPrompt: OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).

You do: independent practice · 10 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Redox: which statement is NOT true? (Oxidation is the loss of electrons. / In a displacement reaction, the more reactive metal is oxidised. / Oxidation and reduction always happen together. / At the anode, ions gain electrons.) → At the anode, ions gain electrons.Prompt: Remember OIL RIG.
  2. Complete the half-equation at the cathode: Al³⁺ + ? e⁻ → Al. How many electrons are needed? → 3Prompt: The charges on both sides must balance.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Predict the products of electrolysis.
  • Use concrete materials: teacher demo or video.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.

Free lesson plan from eurekami.com/lesson-plan-builder

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Oxidation, reduction and half-equations

Name

Date

Score/ 8

  1. Question 1

    Redox: which statement is NOT true?

    • A. Reduction is the gain of electrons.
    • B. Oxidation and reduction always happen together.
    • C. Oxidation is the loss of electrons.
    • D. A metal atom becoming a positive ion is reduced.

  2. Question 2

    Magnesium is added to a solution containing silver ions and displaces the silver. Which species is oxidised?

    • A. magnesium atoms
    • B. silver ions

  3. Question 3

    Complete the half-equation at the cathode: Ag⁺ + ? e⁻ → Ag. How many electrons are needed?

    Answer

  4. Question 4

    Zinc is added to a solution containing silver ions and displaces the silver. Which species is oxidised?

    • A. zinc atoms
    • B. silver ions

  5. Question 5

    Complete the half-equation at the cathode: Al³⁺ + ? e⁻ → Al. How many electrons are needed?

    Answer

  6. Question 6

    Iron is added to a solution containing copper ions and displaces the copper. Which species is reduced?

    • A. iron atoms
    • B. copper ions

  7. Question 7

    Complete the half-equation at the cathode: Zn²⁺ + ? e⁻ → Zn. How many electrons are needed?

    Answer

  8. Question 8

    Complete the half-equation at the cathode: Na⁺ + ? e⁻ → Na. How many electrons are needed?

    Answer

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Answer key: Oxidation, reduction and half-equations

  1. 1. D. A metal atom becoming a positive ion is reduced.

  2. 2. A. magnesium atoms

  3. 3. 1

  4. 4. A. zinc atoms

  5. 5. 3

  6. 6. B. copper ions

  7. 7. 2

  8. 8. 1