Horrible Science: Luna the Magician - Mixes

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What happens when materials dissolve and mix?

Image of salt being stirred into a glass of water.

Sometimes, when you add a solid to a liquid, it looks like it has vanished, as you can no longer see it in the liquid. However, it hasn’t vanished at all.

When a solid like salt is added to water, it can dissolve into it. This means the tiny pieces of the solid spread out evenly through the liquid to form a solution. The salt is still there; it’s just mixed so well that you can’t see it anymore.

This is a reversible change. The salt can be separated from the water again by letting or making the water evaporate.

Image of salt being stirred into a glass of water.
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Watch: Luna the Magician - Mixes

The magic of mixing! It’s not magic, it’s definitely science, but try telling Luna that!

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What is dissolving and mixing?

Image of Horrible Science character Luna with her hands up doing a magic trick. The waiter and the customers look fed up in the restaurant.

Dissolving happens when a solid mixes evenly into a liquid to make a solution. For example:

  • salt dissolves in water
  • sugar dissolves in tea

Not all solids dissolve. For example:

  • sand will sink to the bottom when placed in water
  • flour does not dissolve either - it forms a suspension

A suspension is a cloudy mixture where the fine particles of the original material (such as bits of flour) stay spread throughout the water.

Image of Horrible Science character Luna with her hands up doing a magic trick. The waiter and the customers look fed up in the restaurant.
A spoonful of salt in a beaker of water with some salt at the bottom too.
When this salt is mixed and dissolves into water it will look like it has disappeared.

How can you get a solid back from a solution?

Dissolving is a reversible change, which means the original material can be recovered from the liquid.

If you leave a salt solution somewhere warm, the water will evaporate into the air, as water vapour. Evaporation happens when a liquid changes into a gas.

When the water evaporates, the solid salt is left behind.

This shows that dissolving does not make a new material, it just mixes things in a way that can be undone. It is a reversible change.

A spoonful of salt in a beaker of water with some salt at the bottom too.
When this salt is mixed and dissolves into water it will look like it has disappeared.
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Horrible Science

Every time you swim in the sea, you’re swimming in a giant salt solution. The Dead Sea in Asia is so salty that people can float easily in it without even trying.

That’s because dissolved salt makes the water denser (more tightly packed) helping objects stay on the surface.

Find out more about reversible and irreversible changes.

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How to use Horrible Science in the classroom

If you're looking to bring energy, humour and curriculum-aligned content into your science lessons, Horrible Science might just be your new secret weapon.

How to use Horrible Science in the classroom
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