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Q & A: Mixing stuff

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Most recent answer: 10/22/2007
Q:
what happens when you add something to a pure substance?
- Anonymous
A:
A pure substance is stuff that's made up out of only one kind of molecule. Adding something else usually gives you a mixture of the two substances, but other stuff can happen too. Here are some examples.

Pure substance: liquid water. Additional stuff: salt. The salt will dissolve in the water, and dissociate into its ions. If the water is frozen, the salt will sit on top, and may lower the melting point below the outside temperature. (Then it could slowly dissolve into some liquid- see our other answers on salt and ice.) If the temperature is really cold, the salt will just sit on top of the ice.

In general, if the pure substance and the extra stuff are nonreacting solids, they will just sit on top of each other.

They could form a suspension -- bits of the stuff floating around in the pure substance. Example: oil and water. Or dust in the air.

They could undergo a chemical reaction. Example: water and metallic sodium (please don't try this! Not only does this combination explode by burning hydrogen which is a product, but it throws off sodium hydroxide, which is caustic and poisonous.)

A trivial example: if the "something" is just more of the same pure substance, you just have a bigger collection of the substance.

Tom

(published on 10/22/2007)

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