When we can actually see the different substances, we call the mixture heterogeneous.
Making cookies is a good way to demonstrate a heterogeneous mixture. They can see the different things that go into the cookie dough.
Once mixed up, they can still see the individual components that make up the cookie dough. It is a heterogeneous mixture.
|Erupting Lava Bottle, 2012|
A lot of heterogeneous mixtures are suspensions. A suspension is a mixture where larger particles mixed into smaller particles with the larger particles suspended throughout the mixture. Making an Erupting Lava Bottle is a fun way to demonstrate suspensions.
Adding some raisins to some carbonated water is another way. It is a colloid suspension. A colloid suspension contains particles of solid, liquid, or bubbles of gas suspended within a solid, liquid or gas. At first the raisins sink to the bottom of the glass. However the carbon dioxide is suspended in the liquid and attaches to the raisins. The carbon dioxide is a gas and gases have a tendency to expand and escape their containers, so as the gas bubbles rise, they take the raisins with them.
You can also separate the fat globules from a homogeneous milk mixture by making your own butter. Fill a jar half-full of cream and put the lid on tightly. Put a marble in the jar. Shake the jar for a long time. The fat globules will begin to find other fat globules until they form a large ball of them, otherwise known as butter.
|Making Butter, 2012|
Foam is another kind of colloid. It is made by mixing a gas in a liquid. Whipped cream is a foam of air and cream.
Salad dressing is another kind of colloid called an emulsion. Droplets of liquids mixed with another liquid is called an emulsion.
|The Science of Making Salad Dressing, 2008|
Homogeneous MixturesHomogeneous mixtures are so well mixed that you can't easily see the individual parts.
|The Effect of Temperature on the Solubility of Solid Solutes, 2010|
A solution is made up of one substance that is dissolved into another substance. In the case of a saltwater solution, the solute is the salt, or the substance being dissolved. The water is the solvent since it is the something that is doing the dissolving.
A concentration has a large amount of solute in the solvent. You can demonstrate the effect of concentration by changing the amount of concentration of vinegar in a glass and then adding a Tums tablet to each glass. Look at the varying rates of dissolving.
Water is considered the closest thing to a universal solvent that is known to us. Because of it's chemical properties, many other substances are able to dissolve in water.
|Water's Polarity, 2010|
It is a universal solvent because the water molecules have two positive charges on each end and a negative charge in the center.
When a solute is added to water, the water molecules surround parts of the solute. If the solute has a positively charged part the negative side of the water molecule is attracted to and attaches to the solute molecule. If the solute has a negatively charged part, the positive side of the water molecule is attracted to and attaches to the solute molecule. This is called a polar molecule or a polar bond. A nonpolar molecule, such as oil won't dissolve in water.
|Involving Dissolving, 2008|
Rainbow Milk: The Bonds of Soap
Soap has a nonpolar end and a polar end as well. The nonpolar end is hydrophilic, or water-loving and the polar end is hydrophobic, or water-fearing or fat-loving. You can see the results of this with a bowl of milk, dishwashing liquid and some food coloring.
Add a few drops of food coloring to the bowl of milk. This will help you to see the action the molecules are taking. Now drop some drops of dishwashing liquid in the milk.
The molecules of fat move in every direction as the dishwashing liquid molecules swirl about to join the fat molecules. As the soap breaks down the fats in the milk, it moves in currents, which move and mix the colors.
Alloys and Malleability
Alloys are metals that have been dissolved into other metals to form a metal solution. Most jewelry is made of alloys. Most gold jewelry, for example, is an alloy made up of mainly gold mixed with copper or nickle. This is done to make the gold much harder.
You see, gold is very malleable, or easy to bend. If you made jewelry out of pure gold, it would be as malleable as aluminum foil. To demonstrate this, you can invite your students to sculpt out of aluminum foil.
|Separating a Mixture, 2010|
There are many ways to separate a mixture:
A fun way to demonstrate this is to give your students a mixture and see if they can separate the components using one or more of these methods.
Chomatography is another way of separating mixtures. The markers become the test substances, and are used to draw lines onto strips of paper coffee filter, which are the medium. The strips of paper are then taped to sticks, so that they can be suspended in water, which is the solvent. The solvent passes through the test substance, and as it does so some of the test substance is attracted to the solvent and follows it up the medium. Different types of molecules are transported different distances, causing them to separate.
sources and resources:
- Exploring Creation with Chemistry and Physics, Jeannie Fulbright
- Exploring Creation with General Science, Jay Wile
- Great Explorations in Math and Science, Involving Dissolving
- Exploring Creation with Physical Science, Jay Wile
- Exploring Creation with Chemistry, Jay Wile