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Mixtures Around YouTwo classic examples of mixtures are concrete and salt water. If you live near the ocean, they surround you every day. Even if you're inland, you need to remember your tap water also has many compounds inside, and they act the same way salt would. That is, concrete is a mixture of lime (CaO)/cement, water, sand, and other ground-up rocks and solids. All of these ingredients are mixed together. Workers then pour the concrete into a mold and the concrete turns into a solid (because of the cement solidifying) with the separate pieces inside.
While the cement hardening might be a chemical reaction, the rocks and gravel are held in place by physical forces. They are included in the mixture to increase the strength of concrete. The rocks and gravel are not chemically bonded to the cement. The gravel is also not evenly distributed. There are pieces of gravel here and there. The concentrations of gravel change from area to area. Salt water is different. First, it's a liquid. Second, it's an ionic solution. The salt is broken up into sodium (Na) and chloride (Cl) ions in the water.
You might be wondering why concrete and salt water are not new compounds when they are mixed together. The special trait of mixtures is that physical forces can still remove the basic parts. You can take the solid concrete and grind it up again. The individual components can then be separated and you can start all over. Salt water is even easier. All you have to do is boil the water off and the salt is left, just as if you never mixed the two compounds. Putting Together And Breaking Apart The thing to remember about mixtures is that you start with some pieces, combine them, and then you can do something to pull those pieces apart again. You wind up with the same molecules (in the same amounts) that you started with. The way you separate the molecules is as unique as the mixture. We have talked about grinding and boiling. If you have a mixture of salt and tiny pieces of iron, you could use a magnet to separate the iron from the mixture. 
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