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What you'll need
Iron is a crucial component of a balanced diet (there should actually be enough iron in your body to make one or two small nails), but some people might not consume enough iron naturally to sustain themselves. Because of this, many food manufacturers add iron to some foods to boost the average daily intake of this important mineral. Some foods may use a chemical form like ferric orthophosphate (FePO4) or ferrous sulfate (FeSO4), but most cereals simply use elemental (i.e. the pure atom) iron (Fe), also called "Reduced Iron".
The iron you see in your cereal is elemental iron- actual metallic iron filings or shavings similar to the little flakes you might see come off of a steel wool pad when you squeeze or rub it, just much smaller. That's right, you're eating metal in the morning! But not to worry, acids in your digestive tract can change this metallic iron into a form that is easily absorbed and used by your body. [Note: if you don't see any iron particles in this experiment you probably have a cereal that add one of the chemical forms listed above, so try a different cereal instead.]
These very tiny metal particles are mixed into the rest of the cereal ingredients, which is why you don't normally see them, but a magnet will attract these small iron filings that are present in the cereal, separating them from the other cereal components which are not attracted to the magnet (there's more information about magnetism in the reference links below). Crushing the cereal and mixing it with water makes it much easier to separate the iron. By the way, this is also why you need to use a wooden popsicle stick or plastic spoon to stir in Step 8 of the procedure above (if your cup doesn't have a lid). Most metal spoons are made of steel, which contains a lot of iron and therefore will also be attracted to your magnet (although some types of steel are actually not very magnetic at all).
Separating iron from cereal requires a powerful magnetic field, which is why we need to use a strong neodymium magnet, which is actually made from the elements neodymium, iron and boron (Nd2Fe14B). Neodymium is rarely found in nature, so these magnets are sometimes called Rare Earth magnets. They are usually plated with a thin layer of another metal like nickel, which makes they appear to be metal, but they are actually a type of ceramic, which is more like glass, so they are fragile and can shatter or break quite easily, often producing sharp edges, if you allow them to slam together. Because of this as well as their strength they must be handled very carefully.
Some breakfast cereals contain much more iron that other cereals. You can find out how much iron any cereal contains by reading the "Nutrition Facts" labels on the side of the box (like the photo above). For example, "Total" cereal contains 100% of the recommended daily iron allowance, while "Shredded Wheat" contains a mere 8% - this is why you should see more iron filings from the Total cereal. Test several different cereals, does the amount of iron you see agree with the information on the labels? Is it important that you use the same amount of each cereal and shake it for the same length of time? Is it important to use the same amount of water? Why or why not?
variations and related activities
If you hold your magnet near a flake of piece of the cereal, does it move? What if you crush the cereal into smaller pieces? Try floating a piece of cereal in a bowl of water, then holding the magnet very close. Does it move now?
Another way to do this experiment is to place your magnet inside a small balloon, squeeze out any air inside, then tie it. Now simply drop the balloon into your bowl of mashed cereal and water mixture, attach the lid and shake several minutes as before. Open the lid, remove the balloon and rinse it with water to see the iron filings stuck to the balloon.
If you want to try another cool science experiment with your left over cereal (although it has nothing to do with iron or metal), check out the "Cheerios Effect" (see reference link below). As the name suggests, it works best with Cheerios, but try it with other cereals too.
References and links to more information
Other variations of this experiment:
Why iron is so important for your body:
Which breakfast cereals have the most iron:
Iron and magnetism (ferromagnetism):
The Cheerios Effect (and how it affects bugs that walk on water):
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