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Welcome to the Chemistry unit on mixtures.

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Thursday, April 15, 2010

Mixtures

Most of the matter we encounter consists of mixtures of different substances. Each substance in a mixture retains its own chemical identity and hence its own properties. Whereas pure substances have fixed compositions, the compositions of mixtures can vary. A cup of sweetened coffee for example, can contain either a little sugar or a lot. The substances making a mixture (such as sugar and water) are called components of the mixture.

Some mixtures, such as sand, rocks, and wood, do not have the same composition, properties, and appearance throughout the mixture. Such mixtures are heterogeneous. Mixtures that are uniform throughout are homogeneous. Air is a homogeneous mixture of the gaseous substances nitrogen, oxygen, and smaller amounts of other substances. The nitrogen in air has all the properties that pure nitrogen does because both the pure substance and the mixture contain the same nitrogen molecules. Salt, sugar, and many other substances dissolve in water to form homogeneous mixtures. Homogeneous mixtures are called solutions.
(Brown, 2003)
1) Think about what would be considered a "pure substance" or a solution. What household items are pure and which have more than one ingredient in them?
2) Classify each of the following as a pure substance or a mixture; if a mixture, indicate whether it is homogeneous or heterogeneous:
  • (a) rice pudding;
  • (b) seawater;
  • (c) magnesium;
  • (d) gasoline;
3) Use Split-Page Notetaking strategy to research online the assigned topic: Characteristics of Heterogeneous and Homogeneous Mixtures.