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Science lesson plan · 6th grade (Year 7 in England) · 30 minutes

Choose the right technique to separate a mixture

Materials and their properties

CCSS NGSS.MS-PS1-2England: KS3 Chemistry: Pure and impure substances

Objective and success criteria

Students will: Choose the right technique to separate a mixture.

  • 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: Separating mixtures; Solutes, solvents and how much will dissolve

Leads to: Alkanes and the fractions of crude oil

Materials: A tray of everyday objects, Sorting hoops, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (Separating mixtures; Solutes, solvents and how much will dissolve). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which method is best to separate iron nails from wood shavings? (sieving / filtering / evaporating / using a magnet) → using a magnetPrompt: Is anything dissolved? Is anything magnetic? Are the bits different sizes?
  2. Which word describes this: the liquid that does the dissolving? (solute / solvent / insoluble / saturated solution) → solventPrompt: Solute + solvent → solution.
  3. Which method is best to separate chalk dust from water? (sieving / filtering / evaporating / using a magnet) → filteringPrompt: Is anything dissolved? Is anything magnetic? Are the bits different sizes?

Hook · 3 min

  • Pass round objects made of different materials and ask why each one was chosen.
  • Share the objective: Choose the right technique to separate a mixture. 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: Which technique is best to separate copper sulfate crystals from its solution?
  • Step 1: Evaporating the solvent leaves a dissolved solid behind as crystals.
  • Step 2: So the answer is: evaporation or crystallisation
  • Answer: evaporation or crystallisation
  • 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. Which technique is best to separate food colourings in a sweet coating? (fractional distillation / filtration / chromatography / simple distillation) → chromatographyPrompt: Is the solid dissolved or not? Do you want to keep the liquid?
  2. A mixture contains iron filings and sulfur powder. What is the quickest way to separate them? (use a magnet / use chromatography / distil them / filter them) → use a magnetPrompt: Which one is magnetic?

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. Which technique is best to separate food colourings in a sweet coating? (fractional distillation / filtration / chromatography / evaporation or crystallisation) → chromatographyPrompt: Is the solid dissolved or not? Do you want to keep the liquid?
  2. Why is the filtrate clear after filtering muddy water? (The mud dissolves / Water evaporates / The solid particles are too big to pass through the filter paper / The filter paper adds chemicals) → The solid particles are too big to pass through the filter paperPrompt: Filter paper has tiny holes.

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: Separating mixtures.
  • Use concrete materials: a tray of everyday objects.
  • 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: Alkanes and the fractions of crude oil.
  • 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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Choose the right technique to separate a mixture

Name

Date

Score/ 6

  1. Question 1

    Which technique is best to separate salt from salt water?

    • A. simple distillation
    • B. filtration
    • C. chromatography
    • D. evaporation or crystallisation

  2. Question 2

    In simple distillation, what is the job of the condenser?

    • A. to filter out solids
    • B. to heat the mixture
    • C. to dissolve the salt
    • D. to cool the vapour so it turns back into a liquid

  3. Question 3

    Which technique is best to separate food colourings in a sweet coating?

    • A. fractional distillation
    • B. evaporation or crystallisation
    • C. chromatography
    • D. simple distillation

  4. Question 4

    A mixture contains iron filings and sulfur powder. What is the quickest way to separate them?

    • A. use a magnet
    • B. use chromatography
    • C. filter them
    • D. distil them

  5. Question 5

    Which technique is best to separate the dyes in black ink?

    • A. simple distillation
    • B. filtration
    • C. fractional distillation
    • D. chromatography

  6. Question 6

    Why is the filtrate clear after filtering muddy water?

    • A. The solid particles are too big to pass through the filter paper
    • B. The mud dissolves
    • C. The filter paper adds chemicals
    • D. Water evaporates

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Answer key: Choose the right technique to separate a mixture

  1. 1. D. evaporation or crystallisation

  2. 2. D. to cool the vapour so it turns back into a liquid

  3. 3. C. chromatography

  4. 4. A. use a magnet

  5. 5. D. chromatography

  6. 6. A. The solid particles are too big to pass through the filter paper