Simple Science Experiments: Separating Mixtures



When you see a couple of things mixed together, it is called a mixture. For example: rocks and sand, and a salad with lettuce, tomatoes, and croutons. Another type of mixture is called a “solution;” this is where a solid, like salt, dissolves into a liquid, like water. As you can imagine, it is easier to take apart a mixture like the rocks and sand versus the salt and water.

This month’s experiment is more of a challenge to see if you are able to think of ways to separate several different mixtures.

The challenges are listed after the materials. Before you get started, list as many different ways as you can think of to separate the mixture. The point of this experiment, is to try to think of as many ways as possible, not necessarily just the first thing you thought of. Test as many ways as you can think of, but time them to see which was the quickest. Usually the first thought of method is not the fastest.

Materials:

  • rocks
  • gravel
  • sand
  • water
  • plastic bowls your parents don’t mind getting dirty
  • funnels
  • empty two liter soda bottles, (if you cut off the top, you have a great container with a funnel!)
  • salt
  • spoons
  • tweezers
  • sieves (like a spaghetti strainer)
  • coffee filters
  • and anything else you can think of to help you separate the following:

Different sized rocks
In a big plastic bowl or a 2 liter soda bottle that has had its top cut off, mix several handfuls of different sized rocks, gravel, and sand. Separate them!

Mud, gravel and water
This works best in the clear soda bottle with the top cut off. Mix a handful of dirt, gravel, sand, grass, and water into the bottle. Separate them (including the water!)

Sand and salt
This one calls for some tricky thinking. In a cup, mix together equal parts sand and salt. Separate them!

Hints:

Read this section only if you’re stuck for ideas. Remember, you’re trying to find multiple solutions for each problem, and there is no “right” answer. Whatever works is what you’re going for.

Different sized rocks:
The biggest rocks can be picked out easily. Not so much for the tiny pieces. When you get there, use a sieve (like a spaghetti strainer). Only the smallest pieces will go through.  An alternative that I use as an example in class about natural separation is to mix them all in the soda bottle and just shake it up gently. I won’t spoil the surprise.

Mud, gravel, and water:
First I would sit and wait for this one to settle. Really small things will stay in the water (making it look muddy) for longer than the big chunks. I would then slowly use the coffee filter and funnel somehow… see if you can get the water to look clean.

Sand and salt:
This is the toughest one because the size of the sand and salt particles are so similar. Picking them apart would take forever, using a sieve won’t work because they’re the same size. If you go back to the beginning of the article, you can see a clue that involves something called “solutions.”

Not quite enough of a hint? If you mix the salt and sand with water, only one of them will dissolve… the salt. At that point you can use the coffee filter again to filter out the sand. If you want, see what happens when you let this water sit around for a day or two (or boil it if you get impatient). 

Experiment further:

Can you make other types of mixtures or solutions and try to devise ways to separate them? Perhaps a mixture containing magnets and rocks? Be creative and think like a scientist.

I hope you enjoyed this simple experiment and learned a little bit about mixtures. If you have more questions about this, or need tips about science fair ideas around this topic (or others), contact the author.

Steve Davala is a middle school science teacher who likes to write. He’s got two kids of his own and subjects them to these science activities as guinea pigs. Follow him on Twitter or on www.stevedavala.com.

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