What's the difference between a substance and a mixture?

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These terms are often loosely applied in everyday language, but they have very specific definitions in chemistry. At the root of these definitions are the ideas of chemical bonds and chemical properties.

All matter is composed of atoms, and these atoms can associate, or bond, with other atoms in...

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These terms are often loosely applied in everyday language, but they have very specific definitions in chemistry. At the root of these definitions are the ideas of chemical bonds and chemical properties.

All matter is composed of atoms, and these atoms can associate, or bond, with other atoms in a huge variety of ways. Some of these relationships are very common, such as two hydrogens associated with one oxygen; we call this water. Water has distinct chemical properties that basically disappear if we remove any part of the water compound; oxygen and hydrogen, by themselves, do not act like a "fraction" of water. We would consider water a substance because it cannot be broken down into its components without destroying some of its relationships - that is, its chemical bonds.

A mixture involves two or more substances that are close to each other, but are not chemically bonded. For example, we know that oil and water do not mix; the reason for this is based on the chemical properties of the oil and the water. However, if we put oil and water into a bucket and swirl them together, we can get a mixture; the two substances are occupying the same space, but there isn't much order to their relationship with each other, and we can easily separate them back into oil and water again. Mixtures can always be separated into their ingredients without breaking any chemical bonds.

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