A mixture contains two or more substances that are not chemically combined. Each substance retains its original properties, and can be separated by physical means. Challenge your student to design a method to separate a mixture into its separate components.
First, you’ll need to make the mixture that will be separated. A suggestion would be to mix salt, sand, pebbles, and iron filings. Home improvement stores sell “play sand” which works well for many science experiments, and you can order iron filings from the internet. The base of your mixture should be sand, then add the other substances in slightly smaller quantities.
Here are the steps of the experiment:
1. Have your child observe the mixture and guess the substances from which it is made.
2. Explain the scientific definition of a mixture and give your child a sample of each of the individual substances in the mixture.
3. Ask your child to brainstorm the physical properties of each of the individual substances. (If they don’t come up with these on their own, lead them to include that salt dissolves in water, pebbles are much larger than the other ingredients, and iron is magnetic.)
4. Ask your child to brainstorm how the physical properties of the substances could be used to separate each from the mixture. Depending on the age of the child, you may or may not have to help with this step. You can also lead them to experiment with the individual substances by seeing which will dissolve in water and which are attracted to a magnet, etc.
5. Once your child has developed a plan to separate the mixture, help them carry it out. Here are a few suggestions to successfully separate the four ingredients:
PEBBLES – Separate the pebbles either by picking them out individually with tweezers or fingers, or by straining them out. A colander or a piece of window screen works well as a strainer.
IRON FILINGS – The small iron fragments can easily be pulled from the mixture with a magnet. To keep the magnet clean, put it inside a plastic baggie. After you have collected the iron filings on the outside of the bag, pull the magnet away from the plastic and the filings will be released.
SALT – Pour the mixture into a container of water and stir well until the salt has had time to dissolve completely. Pour off the water. To demonstrate that the procedure worked, evaporate the water to reveal the salt left behind.
SAND – Once the other three ingredients have been removed, the (wet) sand will be left behind.
6. Emphasis that your child has proven that the original material was a mixture because the individual parts were separated by physical means.
