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Chemistry notebook Cambridge IGCSE 0620

Pupil sheet · Crystallisation

Collect the crystals. Follow the liquid. — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. explain

Match the materials to their destinations after filtering the cooled mixture. Explain why solid crystals and dissolved salt take different routes.

Write the number of the matching option.

  1. Residue on the paper
  2. Filtrate in the beaker
  • Solid crystals: ______
  • Water in the remaining liquid solution: ______
  • Dissolved salt: ______

Why do crystals and dissolved salt take different routes?

Nudge (only if you are stuck): Which salt is present as grains? Which is still part of the liquid solution?

2. explain

Order the main stages from a prepared solution to collected crystals. Give a reason for filtering and for blotting.

Write the number of each step in order.

  1. Blot crystals between fresh filter papers
  2. Filter the cooled mixture
  3. Concentrate gently and test a cooled drop
  4. Stop heating and cool/stand
  • First: ______
  • Second: ______
  • Third: ______
  • Fourth: ______

Why filter, then blot?

Nudge (only if you are stuck): What must form before the filter can retain it? What liquid is blotting meant to remove?

3. explain

The filtrate is clear and blue. A student labels it ‘pure water’. Evaluate the label and account for salt on the paper and in the receiver.

Evaluate the claim

Account for salt in both destinations

Nudge (only if you are stuck): Which salt became solid? What happened to the part still dissolved?

4. explain

Plan a complete method to collect hydrated blue crystals from prepared copper(II) sulfate solution. Explain when to stop heating, when to filter and how to dry the crystals without changing their structure.

Sequence from the prepared solution, with reasons

Collection and why its position in the sequence matters

Drying choice: what is removed and what remains?

Nudge (only if you are stuck): Is liquid on a crystal's surface the same as water within its structure?

5. explain

A prepared solution contains a wanted salt and a soluble impurity. On cooling, the salt crystallises while the impurity stays dissolved. Describe how to collect the crystals. Explain where most impurity goes and why perfect purity isn't guaranteed.

Collection and drying

Impurity destination

Limit to the purity claim

Nudge (only if you are stuck): What passes through with the liquid? Could some of that liquid remain on the crystals?