Take Home Lab #4

Take Home Lab #4

Question: What state of matter is a colloid?

Safety: Do not try to save the cornstarch and reuse it. Mold grows quickly on cornstarch once it is wet, so dispose of it immediately. Wipe up any spills immediately. Do not consume the cornstarch after use. Dispose of the material in the trash.

Materials: shallow bowl, water, cornstarch

Procedure: The kinetic molecular theory helps one understand the difference between solid, liquid, gas, and plasma. A solid has a definite shape and volume. A liquid has a definite volume and takes the shape of its container. A gas fills its container completely and its volume changes with temperature and pressure.  A plasma fills its container and has a variable volume.

            In this lab, you will investigate a material called a colloid to determine its state of matter. You will see that determining the state of matter is not always as easy as it sounds. Colloids are not a separate state of matter, but they sure can act strangely.

1. Make the cornstarch colloid by adding 4 spoonfuls of cornstarch to 2 spoonfuls of water. It should be very thick but not dry. Make small adjustments by adding a little more starch or a little more water. It will dry out a little over time; just add more water to get the colloid back to its original condition. The colloid should get to the point where you can pick up a chunk of it and it turns into a liquid in your hand.

2. After each of the following tests, determine whether the colloids acted like a liquid or a solid:

            a. Tap the surface of the colloid quickly with your finger. Is it a solid or a liquid? __________

            b. Press your finger slowly into the colloid. (it will not hurt you; it actually makes your skin soft and will rinse off with water.) Is it a solid or a liquid?__________

            c. Try to stir the colloid quickly with your finger. Is it a solid or a liquid? __________

            d. Try to stir the colloid slowly with your finger. Is it a solid or a liquid? __________

            e. Tip the bowl from side to side. Is it a solid or a liquid? _________

            f. Grab a chunk and pick it up. Is it a solid or a liquid? __________

            g. Pour it from the bowl to your hand. Is it a solid or a liquid? _______

            h. Set objects of different densities on its surface. Is it a solid or a liquid? _________

Post-Lab Questions:

1. Is this colloid a solid or a liquid? Explain.

2. Many fine powders, such as the silt on the side of a river, can form colloids. Would it be dangerous to build homes or businesses on these riverbeds? Explain. Try a little experiment with your colloid to see what might happen.

3. Do you think you could make a colloid from salt, sugar, or baking soda? Based on your answer, which is one condition that must be met for a powder to form a colloid?