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Science lesson plan · 6th grade (Year 7 in England) · 60 minutes

Spot the evidence that a chemical reaction happened

Chemical reactions, acids and bases

CCSS NGSS.MS-PS1-2England: KS3 Chemistry: Chemical reactions

Objective and success criteria

Students will: Spot the evidence that a chemical reaction happened.

  • 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: Physical and chemical changes

Leads to: Conservation of mass in reactions

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 · 6 min

  • Quick retrieval from earlier learning (Physical and chemical changes). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Is this a physical or a chemical change: sugar dissolving in tea? (physical change / chemical change) → physical changePrompt: Is a new substance made?
  2. A nail left outside turns orange-brown and flaky. What has happened? (Paint fell on it / The nail dissolved / The nail melted / Iron reacted with oxygen and water to make rust) → Iron reacted with oxygen and water to make rustPrompt: Rusting needs both air and water.
  3. Physical and chemical changes: which statement is NOT true? (In a chemical reaction, atoms are rearranged to make new substances. / All bubbles mean a chemical reaction. / Rusting needs both oxygen and water. / Burning is a chemical change.) → All bubbles mean a chemical reaction.Prompt: Does each change make a new substance?

Hook · 6 min

  • Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
  • Share the objective: Spot the evidence that a chemical reaction happened. Read the success criteria together.

I do: model it · 12 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: What evidence of a chemical reaction is shown here: a shiny iron nail slowly turns orange-brown in damp air?
  • Step 1: A new colour can show a new substance has formed.
  • Step 2: So the answer is: a colour change
  • Answer: a colour change
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 12 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. What evidence of a chemical reaction is shown here: a hand warmer gets hot when opened? (a gas is given off / a colour change / a solid (precipitate) forms / an energy change (heat or light)) → an energy change (heat or light)Prompt: Did you see bubbles, a new colour, a new solid or an energy change?
  2. Which observation is the strongest evidence that burning a candle is a chemical change? (Carbon dioxide and water vapour are made, and energy is released as heat and light / The wax melts / The wick is white / The candle gets shorter) → Carbon dioxide and water vapour are made, and energy is released as heat and lightPrompt: Melting alone is only physical.

You do: independent practice · 17 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 · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Sugar dissolves in tea and seems to disappear. What kind of change is this? (the sugar turns into water / chemical, because the sugar is destroyed / physical, because the sugar is still there and could be recovered / chemical, because the tea gets sweeter) → physical, because the sugar is still there and could be recoveredPrompt: Evaporating the water would leave something behind.
  2. Chemical reactions: which statement is NOT true? (Boiling water is a chemical reaction because bubbles form. / Dissolving salt in water is a physical change. / Rusting is a chemical change. / Many chemical reactions are hard to reverse.) → Boiling water is a chemical reaction because bubbles form.Prompt: Is a new substance always made when bubbles appear?

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: Physical and chemical changes.
  • 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

  • Move on to: Conservation of mass in reactions.
  • 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-6.

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

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Spot the evidence that a chemical reaction happened

Name

Date

Score/ 8

  1. Question 1

    What evidence of a chemical reaction is shown here: a cut apple turns brown?

    • A. a gas is given off
    • B. a colour change
    • C. a solid (precipitate) forms
    • D. an energy change (heat or light)

  2. Question 2

    Chemical reactions: which statement is NOT true?

    • A. In a chemical reaction, new substances are made.
    • B. Dissolving salt in water is a physical change.
    • C. Many chemical reactions are hard to reverse.
    • D. Boiling water is a chemical reaction because bubbles form.

  3. Question 3

    Bread is toasted and goes brown and crisp. What kind of change is this?

    • A. physical, because it is only heated
    • B. no change at all
    • C. physical, because it is still bread
    • D. chemical, because new substances form that cannot be turned back into bread

  4. Question 4

    Sugar dissolves in tea and seems to disappear. What kind of change is this?

    • A. chemical, because the tea gets sweeter
    • B. the sugar turns into water
    • C. chemical, because the sugar is destroyed
    • D. physical, because the sugar is still there and could be recovered

  5. Question 5

    What evidence of a chemical reaction is shown here: an instant cold pack gets cold when squeezed?

    • A. a gas is given off
    • B. a colour change
    • C. a solid (precipitate) forms
    • D. an energy change (heat or light)

  6. Question 6

    What evidence of a chemical reaction is shown here: limewater turns cloudy?

    • A. a gas is given off
    • B. a colour change
    • C. a solid (precipitate) forms
    • D. an energy change (heat or light)

  7. Question 7

    Ice melts into water. A student says this is a chemical reaction because it changes. Why is this wrong?

    • A. Melting releases a new gas
    • B. Ice and water are different elements
    • C. All changes are chemical reactions
    • D. No new substance forms: it is still water, so it is a physical change

  8. Question 8

    What evidence of a chemical reaction is shown here: a glow stick gives out light when bent?

    • A. a gas is given off
    • B. a colour change
    • C. a solid (precipitate) forms
    • D. an energy change (heat or light)

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Answer key: Spot the evidence that a chemical reaction happened

  1. 1. B. a colour change

  2. 2. D. Boiling water is a chemical reaction because bubbles form.

  3. 3. D. chemical, because new substances form that cannot be turned back into bread

  4. 4. D. physical, because the sugar is still there and could be recovered

  5. 5. D. an energy change (heat or light)

  6. 6. C. a solid (precipitate) forms

  7. 7. D. No new substance forms: it is still water, so it is a physical change

  8. 8. D. an energy change (heat or light)