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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 sand from water? (sieving / filtering / evaporating / using a magnet) → filteringPrompt: Is anything dissolved? Is anything magnetic? Are the bits different sizes?
  2. Which word describes this: sand that sinks to the bottom of water? (solvent / solution / saturated solution / insoluble) → insolublePrompt: Solute + solvent → solution.
  3. Which method is best to separate steel paper clips from plastic beads? (sieving / filtering / evaporating / using a magnet) → using a magnetPrompt: 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 ethanol from a mixture of ethanol and water? (simple distillation / fractional distillation / filtration / evaporation or crystallisation) → fractional distillationPrompt: 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 / distil them / use chromatography / 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 ethanol from a mixture of ethanol and water? (simple distillation / evaporation or crystallisation / fractional distillation / chromatography) → fractional distillationPrompt: 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 / desalination by distillation or reverse osmosis / chromatography / filtration through sand only) → desalination by distillation or reverse osmosisPrompt: Dissolved salt cannot be removed by a simple filter.

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

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

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

  2. Question 2

    Which technique is best to separate the fractions in crude oil?

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

  3. Question 3

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

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

  4. Question 4

    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

  5. Question 5

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

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

  6. Question 6

    Which technique is best to separate drinkable water from muddy salty water on a survival course?

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

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Answer key: Choose the right technique to separate a mixture

  1. 1. A. to cool the vapour so it turns back into a liquid

  2. 2. D. fractional distillation

  3. 3. A. fractional distillation

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

  5. 5. D. chromatography

  6. 6. A. simple distillation