Differing Densities Teacher’s Guide:1/31/08
By RT Tourek
Key Concepts:
Here we will explain the differences of liquid densities. Liquids with higher densities will automatically sink to the bottom of a mixture while liquids with a low density will rise to the surface of a liquid. The mixture should level itself out, creating different layers in the container. The ideas of miscible liquids (liquids that mix together) and immiscible liquids (liquids that cannot be mixed together) should be introduced. Also, the idea of suspension (A system in which microscopically visible particles are dispersed throughout a less dense liquid or gas from which they are easily filtered but not easily settled because of system viscocity or molecular interactions.) should be introduced
Materials needed for demo:
- 500 mL clear beaker
- 100 mL of Corn Starch
- 100 mL of Milk
- 100 mL of Oil (preferable a different color than the Cornstarch and milk)
- A spoon
- 100mL of
Materials per student for activity:
- Elmer’s glue (enough that a child can make a circle with a 1 inch radius)
- Food coloring
- Toothpicks
- Dixie cups
- 1 mL Syringe
- Small plastic weighing plates.
Procedure:
1.)Place the clear beaker at a location that all are able to view.
2.)Add 100 mL of milk to the 500 mL beaker.
3.)Add 100 mL of oil to the 500 mL beaker. Pause to allow for the separation to be complete and allow the class to observe.
4.)Add 100 mL of corn starch to the 500 mL beaker. Allow for the separation to occur and be observed.
5.)Ask the students which liquid they think has most similar density to water. After a consensus tell them that how they will know is that the liquid with the most similar density will double in size while the other two liquids will still onle look to contain 100 mL.
6.)Take a spoon and mix the solution together so that the layers are not visible any longer. Place to the side and allow for the mixture to settle. Discuss the ideas of Miscible liquids and Immiscible liquids. Start with the given activity below. At the conclusion of the activity, allow for the students to look back at the beaker. While the activity was occurring, the liquids in the beaker should have separated and settled out into their previously viewed layers.
Activity:
At this point, the children should have a little understanding that some liquids are miscible and some are immiscible. They should also have an idea that that the least dense objects are on the lighter and will remain above the denser liquids. We will now apply this knowledge to a project that will produce a craft displaying this concept.
- Take a 1 mL syringe and fill it up with Elmer’s glue from a provided Dixie cup and expel it into a small plastic weighing container. Create a circle with Elmer’s glue by tilting the weighing container.
- Place 1 drop of food coloring in the glue.
- Take a toothpick and maneuver it through the glue. A design should be created where the food coloring should remain and not mix with the glue, leaving a lasting design that should remain dark and a pure dye as the glue hardens.
- After done with design, the weigh container can be placed in a designated area where it will be allowed to harden overnight.
- The next morning, the glue should have hardened and the craft can be removed from the wax paper and taken home as a reminder of this experiment and topics introduced.
This activity should show the different densities of liquids and that because the dye has a lower density than the glue, it will stay above the glue until it hardens. It is a key point to not disturb the weighing containers while the glue crafts are hardening because the slightest bump will disturb the image created.
Cautions:
Children that are allergic to dye should not wear the created craft because it will contain dye.
Reference:
Previous experiment seen in my elementary school science classes. It was also a previous CH151 experiment.
Differing Densities1/31/08
By R.T. Tourek
Draw what you see in the beaker after all three substances are together?
What does the beaker look like after it is mixed with the spoon?
What does the beaker look like at the end of class?
Are the liquids mixed at the end?
MIXEDNOT MIXED