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Science lesson plan · 6th grade (Year 7 in England) · 60 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 · 6 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 dried peas from rice? (sieving / filtering / evaporating / using a magnet) → sievingPrompt: Is anything dissolved? Is anything magnetic? Are the bits different sizes?
  2. Which word describes this: the salt in salt water? (solvent / solute / solution / insoluble) → solutePrompt: Solute + solvent → solution.
  3. Which method is best to separate copper sulfate crystals from a solution? (sieving / filtering / evaporating / using a magnet) → evaporatingPrompt: Is anything dissolved? Is anything magnetic? Are the bits different sizes?

Hook · 6 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 · 12 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 · 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. Which technique is best to separate the dyes in black ink? (chromatography / evaporation or crystallisation / filtration / simple distillation) → chromatographyPrompt: Is the solid dissolved or not? Do you want to keep the liquid?
  2. Countries such as Saudi Arabia get much of their drinking water from the sea. Which method is used on a large scale? (adding more salt / chromatography / filtration through sand only / desalination by distillation or reverse osmosis) → desalination by distillation or reverse osmosisPrompt: Dissolved salt cannot be removed by a simple filter.

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. In simple distillation, what is the job of the condenser? (to heat the mixture / to cool the vapour so it turns back into a liquid / to filter out solids / to dissolve the salt) → to cool the vapour so it turns back into a liquidPrompt: Cold water flows around it.
  2. Which technique is best to separate food colourings in a sweet coating? (filtration / chromatography / simple distillation / evaporation or crystallisation) → chromatographyPrompt: Is the solid dissolved or not? Do you want to keep the liquid?

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/ 8

  1. Question 1

    Why is the filtrate clear after filtering muddy water?

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

  2. Question 2

    Which technique is best to separate ethanol from a mixture of ethanol and water?

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

  3. Question 3

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

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

  4. Question 4

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

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

  5. Question 5

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

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

  6. Question 6

    Which technique is best to separate sand from water?

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

  7. Question 7

    Countries such as Saudi Arabia get much of their drinking water from the sea. Which method is used on a large scale?

    • A. filtration through sand only
    • B. desalination by distillation or reverse osmosis
    • C. chromatography
    • D. adding more salt

  8. Question 8

    Which technique is best to separate copper sulfate crystals from its solution?

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

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Answer key: Choose the right technique to separate a mixture

  1. 1. D. The solid particles are too big to pass through the filter paper

  2. 2. B. fractional distillation

  3. 3. C. use a magnet

  4. 4. D. chromatography

  5. 5. A. chromatography

  6. 6. C. filtration

  7. 7. B. desalination by distillation or reverse osmosis

  8. 8. A. evaporation or crystallisation