Page 52 - Big Ideas Year 9 sciPAD 2025

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52 SCIPAD - BIG IDEAS - BOOK 1
THE NATURE OF MIXTURES
Saturation
A solution becomes saturated when no more solute can dissolve in the solvent. At this point, the
solution has a high concentration of solute. If some of the solvent evaporates from the saturated
solution, it becomes supersaturated, causing crystals of the solute to form.
Growing Crystals
Aim: To make crystals form in a supersaturated solution.
Equipment: Copper sulfate powder, 2 x 250 mL beakers, a pencil or ice-block stick, some cotton
string, a stirring rod, hot water (either provided by your teacher, or made by heating
water over a Bunsen until it is approximately 70°C), a watch glass, a funnel and filter
paper.
Method:
Part 1
1. Pour approximately 150 mL of hot water into a 250 mL beaker.
2. Add a spoonful of copper sulfate powder and stir until it dissolves.
3. Repeat step 2 until no more copper sulfate will dissolve.
4. Filter the solution into a clean 250 mL beaker.
5. Pour a small amount of this solution into a watch glass.
6. Label your watch glass and beaker and place the watch glass on a window-sill
overnight.
Part 2
1. Cut a 12 cm length of cotton string and attach it to a pencil or stick. The string
should be just long enough to sit off the bottom of the beaker when the pencil is
placed across the beaker (refer to diagram).
2. Your watch glass should contain small crystals of copper sulfate. You are going to
use one of these as a ‘seed crystal’. Carefully select one crystal.
3. Make an opening in your string by untwisting the strands of string. This opening
should be near the end of the string (the end that is not attached to the pencil or
stick). Place the seed crystal in between the strands of string and re-twist the string
to secure the seed crystal.
4. Suspend the seed crystal into the saturated copper sulfate solution.
5. Leave your beaker to slowly evaporate.
Observations: 


1. Complete the second part of the diagram to show the size and shape of your crystal.
String
attached to
pencil
Saturated
copper sulfate
solution
Seed crystal
attached to
string
Set up at the start of the investigation Crystal at the end of the investigation
Copper
compounds
are poisonous
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