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Name: Jeanne M.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 2001 - 2002

How can you tell the difference between a compound and a mixture? Is a raw cake a mixture or a compound? A baked cake? A marshmallow?

Jeanne, Compounds are chemical unions of elements that combine (almost always) in definite proportions. In addition, compounds are of uniform composition. The cakes you mention are all mixtures because the proportions can be variable and the materials from which the cake is made do not combine to form a substance of uniform composition. Of course, this does not mean that compounds do not exist before and after baking. Indeed, some of the cake ingredients are themselves compounds. And, too, the baking process produces new compounds when certain ingredients react with each other. That is why the cake looks and tastes different than the batter or individual ingredients.

ProfHoff 391

Hi Jeanne,

A compound is a whole bunch of identical molecules. Sugar is a compound, table salt (if it was pure NaCl would be a compound). A mixture is many different types of molecules. Using strict chemical definitions and if you could identify them only as a MIXTURE or a COMPOUND; a raw cake mixture, a baked cake and marshmallows would all be mixtures.

-Darin Wagner

A chemical compound is a substance composed of specific proportions of chemical elements, that exist in a single phase (gas, liquid, or solid) at a given temperature and pressure. A chemical mixture is a blend of one or more phases of variable composition that can be separated into constituent chemical substances.

So a cake -- baked or raw -- is a mixture of flour, water, and so on. A marshmallow is a mixture of small air bubbles suspended in matrix of sugar, water and other ingredients.

The definitions I have given above cover most cases. There are, like in all definitions, some areas where the distinction may be hard to make -- some gray areas. Such an area might be metal alloys for example.

Vince Calder

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