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Science lesson plan · 6th grade (Year 7 in England) · 30 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 · 4 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: crushing a can? (physical change / chemical change) → physical changePrompt: Is a new substance made?
  2. Which observation shows that a chemical reaction has happened? (A gas is given off and the colour changes / The substance changes shape / Salt dissolves / Ice turns to water) → A gas is given off and the colour changesPrompt: Look for signs of something new being made.
  3. Physical and chemical changes: which statement is NOT true? (Rusting needs both oxygen and water. / Atoms are destroyed in chemical reactions. / Burning is a chemical change. / In a chemical reaction, atoms are rearranged to make new substances.) → Atoms are destroyed in chemical reactions.Prompt: Does each change make a new substance?

Hook · 3 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 · 7 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 · 6 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: fizzing when vinegar is poured on baking soda? (a gas is given off / a colour change / a solid (precipitate) forms / an energy change (heat or light)) → a gas is given offPrompt: Did you see bubbles, a new colour, a new solid or an energy change?
  2. Ice melts into water. A student says this is a chemical reaction because it changes. Why is this wrong? (Melting releases a new gas / All changes are chemical reactions / Ice and water are different elements / No new substance forms: it is still water, so it is a physical change) → No new substance forms: it is still water, so it is a physical changePrompt: Is the substance after the change different from before?

You do: independent practice · 7 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 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 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? (physical, because the sugar is still there and could be recovered / chemical, because the tea gets sweeter / chemical, because the sugar is destroyed / the sugar turns into water) → physical, because the sugar is still there and could be recoveredPrompt: Evaporating the water would leave something behind.
  2. What evidence of a chemical reaction is shown here: limewater turns cloudy? (a gas is given off / a colour change / a solid (precipitate) forms / an energy change (heat or light)) → a solid (precipitate) formsPrompt: Did you see bubbles, a new colour, a new solid or an energy change?

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/ 6

  1. Question 1

    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)

  2. Question 2

    Chemical reactions: which statement is NOT true?

    • A. Dissolving salt in water is a physical change.
    • B. In a chemical reaction, new substances are made.
    • C. Every colour change proves a chemical reaction.
    • D. Many chemical reactions are hard to reverse.

  3. Question 3

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

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

  4. Question 4

    What evidence of a chemical reaction is shown here: two clear solutions are mixed and a yellow solid appears?

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

  5. Question 5

    What evidence of a chemical reaction is shown here: bubbles form when an antacid tablet is dropped in water?

    • 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

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

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

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Answer key: Spot the evidence that a chemical reaction happened

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

  2. 2. C. Every colour change proves a chemical reaction.

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

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

  5. 5. A. a gas is given off

  6. 6. B. chemical, because new substances form that cannot be turned back into bread