Separating Mixtures: Filtration and Crystallisation

Lab Brief #3

🎯 Your mission

Predict it first. Then prove yourself right (or wrong).

⚡ The twist

Mixing two safe things doesn't always make a safe thing.

What you'll learn

Filtration separates an insoluble solid from a liquid: the residue stays on the paper and the filtrate passes through. Crystallisation recovers a dissolved solid by evaporating solvent slowly, allowing an ordered lattice to grow.

Key words

filtrate
The liquid that passes through the filter paper.
crystallisation
The formation of solid crystals as solvent evaporates from a solution.

Make a hypothesis first

Predict: will the mixture get hotter, colder, or stay the same?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

filter funnel
filter paper
beakers
sand
copper sulfate
evaporating basin
stirring rod

Get ready

⚠️ Safety first

Copper sulfate is harmful if swallowed and stains — wear gloves and goggles, wash hands after.
Dispose of copper sulfate solution in the labelled waste container, never down the sink.

Step 1 of 4 · Read

Think about what you just learned: say what "filtrate" and "crystallisation" mean in your own words before you start.

Step 2 of 4 · Do

Separate a mixture of sand and copper sulfate by dissolving, filtering and then crystallising the filtrate. Compare fast evaporation over a flame with slow evaporation on a windowsill and note the difference in crystal size.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

In filtration, the substance left on the paper is the:

How sure are you?😐 maybe

Question 2 of 2

Slow evaporation during crystallisation produces crystals that are:

How sure are you?😐 maybe

Mind = blown

💧 Hot water can freeze faster than cold water under the right conditions. Nobody fully understands why.

Nice work!

You got 0 of 2 right.

Next: Distillation and Chromatography All lessons

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✨ More to explore

🌍 Where you see this in real life: Your toothpaste, your soap, even your breakfast involves this.

🏆 Stretch challenge (try it this week): Ask a grown-up to help you mix two safe kitchen things. Predict what will happen first.

👨‍👩‍👧 For the dinner table: “What's something we cook that mixes things together this way?”

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