Mixtures and solutions
Name: richard e brown
Explain the difference between mixtures and solutions.
Suggest hands-on activities for sixth grade students in those topics.
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
Another seasonal example :)
Fruit cake is a heterogeneous mixture (all those chunks...yeck!) while
a good old pumpkin pie is rather homogeneous.
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
Hope this helps
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.
gregory r bradburn
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Update: June 2012