Mixtures and solutions ```Name: richard e brown Status: N/A Age: N/A Location: N/A Country: N/A Date: 1999 ``` Question: Explain the difference between mixtures and solutions. Suggest hands-on activities for sixth grade students in those topics. Replies: Textbook definition: "Mixtures are formed simply by blending two or more substances together in some random proportion without chemically changing the individual substances in the mixture." Mixtures can then be broken down into homogeneous and heterogeneous. A homogeneous mixture is called a solution: salt or sugar and water, air (solution of gases). These have a constant composition throughout the solution. A heterogeneous mixture would be: salt with sugar (no water), water with gasoline or oil, salt with sand. These have areas with differing compositions (you could usually see the separation of the two things). -Joe Schultz Another seasonal example :) Fruit cake is a heterogeneous mixture (all those chunks...yeck!) while a good old pumpkin pie is rather homogeneous. -JS Mix together some iron filings with some salt. Then, hold a magnet over the mixture and use it to "unmix" the mixture. A rule of thumb; mixtures can be "unmixed" by physical means, while solutions cannot (one would need to boil all the water out of a sugar solution to separate the sugar from the water). Hope this helps prof topper Note that boiling water away is also a physical means -- but what you are separating is gas phase water from liquid phase water. The solid sugar eventually starts to come out of solution also, but only when enough water has boiled away that it is saturated and cannot hold any more sugar in solution. Another "classic" experiment that shows one difference between solutions and mixtures is to shine light through them. For example, dissolve some sugar in water (a teaspoon of sugar in a cup of water) and in another container dissolve an equal amount of milk in water. Now, using a high-intensity flashlight (or, if available, a laser pointer), shine light into the liquids. With a solution (homogeneous at a molecular level) the light passes through without scattering and you can't see the beam in the liquid. The cloudy milk/water sample will scatter the light and you will be able to see the path the light takes through the liquid. The milk will stay in the liquid until it is put in a centrifuge but it is not a solution. It is a suspension of very small particles of fats and other components in water. The light is scattered by these small particles. Have fun! gregory r bradburn Click here to return to the Chemistry Archives

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