Year 7 Science · Unit 2 · Lesson 8
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims...
"Filtering is always the best way to separate any mixture. If you put a mixture through a fine enough filter, you can always get the parts out separately. Scientists should just use filtration for everything — it's the simplest method and it doesn't use heat, so it's safer."
(a) What part of this claim is supported by science you've learned? Give a specific example where filtration is the correct choice and explain why.
(b) What is misleading or wrong about this claim? Give at least two specific examples of mixtures where filtration would NOT work, and explain the scientific reason in each case.
(c) What evidence or information would a scientist need to decide which separation technique to use for an unknown mixture? List the questions they should ask.
1. Iron filings and sulfur powder have been mixed together. Explain why filtration would NOT separate this mixture, and suggest a more appropriate technique. Identify the physical property difference that makes your chosen technique work.
2. Separation techniques work because mixture parts have different physical properties — but they do not break chemical bonds. Explain what this means, and why it is important that separation methods are physical changes, not chemical changes.
Wrap Up
In one sentence, what was the main idea of this lesson?