Salty prism

Grow crystals using ordinary salt! Can you make crystals that are shaped like cubes?

Warning: You will use hot water in this experiment. Be careful not to scald yourself!

You will need:

• a heat-proof container
• a clear glass or beaker
• table salt
• a spoon
• hot water

How to do it:

1. Boil the water, and then let it cool for a few minutes.
2. Carefully pour a small amount of the hot water into the heat-proof container.
3. Add salt to the hot water and stir it with a spoon until the salt dissolves. Keep adding salt and stirring until the salt no longer dissolves.
4. Take your salty water and carefully pour a small amount of the liquid into your glass. Make sure the undissolved salt doesn’t go into the glass!
5. Put your glass in a shady spot and let the water evaporate. Check back over the next few days to see your salt crystals!

Note: If you only have a few cubes, you can use these to ‘seed’ new cubes! Re-do the experiment above, but when the liquid is cool, carefully drop some of the cubes from your previous experiment into the liquid. These will help more crystals grow.

What’s happening?

When you mix the salt into the water until it no longer dissolves, you’re making a saturated solution. This means that the water has dissolved as much salt as it can!

Over time, the water will slowly evaporate (putting it in a sunny spot may make it evaporate too quickly), but the salt won’t. This means that there is less water for the amount of salt in the cup. The extra salt cannot go anywhere so it begins to form a solid.

Table salt is made of sodium ions and chloride ions. These pack together (called nucleation) into a structure like a cube where the sodium ions alternate with the chloride ions at the atomic level. As more and more ions are packed together, they form a cube that you can see.

Crystals have very regular structures and are very pure. Different salts will form different crystal shapes. Try using Epsom salts (magnesium chloride) instead! How does iodised salt crystallise?

You can explore some other regular shapes by using rods and their mirror reflections in the Multi-Mirror exhibit in Wonderworks.

Salty prism
Grow your own salt crystals.

Explore More

Multi-Mirror
What shapes can you make using a few rods and three mirrors? Try making a cube, a pointy pyramid or even a soccer ball.

See more exhibits...

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