Quick check: choosing a separation technique

A few quick questions on choosing and justifying a separation technique, and saying why another one would not work. Taught in class; use this to check yourself.

You are handed a mixture you have never seen. How do you decide how to separate it?

The skill your teacher covers in class: look at the property differences, pick a technique, and say why it works.

Explain: Use the particle model to explain what you saw.

ExplainUse the particle model to explain what you saw.

Choose and justify

Which technique separates this mixture?

Iron filings from sand

Sand from water

Salt from salty water

Pure water from salty water, collecting the water

The colours in a felt-tip ink

A mixture of sand, salt and water is to be separated into all three. Which plan works?Filter out the sand, then evaporate the water to leave the saltEvaporate first, then filterUse a magnet, then filterFilter only

Why will filtering not separate salt from salty water?The holes are too big to catch any solidDissolved salt particles are tiny and pass through the holes in the paper with the waterFilter paper dissolves in waterSalt is too heavy for the paper to hold

I can pick a technique for a mixture, explain it with a property difference, and say why another technique would not work.

For teachers

A self-test on choosing and justifying a separation technique for a mixture, and saying why another would fail (AC9S7U06, node 5, a hinge node taught in class). About 10 minutes.

Open the teacher guide: answers, solutions, slides and a worksheet.

Students will be able to

I can match a mixture to a separation technique.
I can put the steps of a separation in a sensible order.
I can say why one technique would not work on a given mixture.

Before class

A Quick check: a few questions on what students should know for AC9S7U06 node 5, which you teach in class. It has no board, no clip and no new teaching, and it is optional, so it never holds up course completion. Set the width with ?width=minimum, typical (default) or wider.

Use it as a self-test after your teaching, a starter, or revision. The strongest version of this node is on the bench with a mystery mixture. Use these questions to settle the reasoning first, or to review afterwards.

Running the lesson

Do the match first, then ask a student to justify two of them with a property.
The order question links to the sand, salt and water practical.

The hard part (on purpose)

Justifying with a property rather than naming the technique. When a student says "use a filter", ask what the filter paper tests.

When students get stuck

A student says the filter catches sand because it is heavier. Ask: What does the filter paper actually test, weight or size? Fix: Size: sand grains do not fit through the holes; dissolved salt does.
A student would evaporate first when sand is present. Ask: Where does the sand go? Fix: It stays with the salt. Remove the insoluble solid before evaporating.

Stretch and support

Stretch: Design a way to separate salt, sand, iron filings and wood shavings. What is the best order, and why?

Support: Give a table with columns: part, property, technique. Students complete it for each part.

Where it leads

Back in class: a practical separating an unfamiliar mixture, with a written justification.

What each step is for

Choose and justify: Node 5: choose a technique for a mixture using property differences, put steps in order, and explain one that would not work.

Now you can

Match a mixture to a separation technique.
Put the steps of a separation in a sensible order.
Say why one technique would not work on a given mixture.

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