Poppers: How do Immiscible Liquids Behave?
How do immiscible liquids (liquids that do not mix) behave?
- baby-food jar with lid tap water
- red food coloring
- clear liquid
- cooking oil
- magnifying lens
- desk lamp
- Fill the baby-food jar halfway with water.
- Add one drop of red food coloring and stir.
- Slowly add cooking oil to the jar until the jar is almost full.
- Secure the lid and allow the jar to stand undisturbed for 2 minutes.
- Describe the contents of the jar.
- Shake the jar vigorously five times.
- Close one eye and hold the magnifying lens near your open eye.
- With your other hand, hold the jar in front of the lens with the light of the desk lamp behind the jar.
- Study and describe the contents of the jar.
At first, the entire contents of the jar have a pink color, but within seconds two separate layers begin to form: a red layer on the bottom, and a cloudy layer on top. Bubbles are seen rising and falling through the liquids. Many of the bubbles combine, forming larger bubbles.
The oil and water separate because they are immiscible. Shaking the jar produces an emulsion (a suspension of two liquids; some separate upon standing). Immediately after being shaken, bubbles of water and oil are seen throughout the mixture. When left standing, the lighter oil begins to float to the top and the colored water sinks to the bottom of the jar. The spheres of oil move toward each other because the molecules of oil attract each other. The attraction between molecules of the same material is called a cohesive force. This attraction causes smaller bubbles to be pulled apart, pop open, combine, and form larger bubbles. The spheres of water behave like the oil molecules by pulling on each other, causing small bubbles to combine and form larger water bubbles. The two liquids finally separate into a layer of oil that floats on a layer of colored water.
Try It With A Microscope
- With an eyedropper, remove a sample from the jar containing the oil and water that has been vigorously shaken.
- Squirt the liquid into the baby-food jar and then draw it back into the eyedropper. Repeat this action six or seven times to mix the liquid thoroughly.
- Place a drop of the liquid on a microscope slide.
- Observe under low power.
At first, the viewing field is dark and covered with tiny, moving bubbles. The bubbles appear to pop, and combine to form larger bubbles. As the bubbles grow larger and separate, the viewing field becomes lighter.
- How long does it take for the oil and water to completely separate? Repeat the original experiment. Ask a helper to start a timer as soon as you begin to shake the jar. At 100minute intervals, use a magnifying lens to observe each layer, and record the time when no bubbles are observed.
- Does the amount of shaking affect the time required for separation? Repeat the original experiment, but prepare two separate jars with equal amounts of oil and water in each. Shake one of the jars 5 times and shake the other jar 30 times. Allow both jars to sit undisturbed, and use a magnifying lens to determine when no bubbles are present in the separate layers.
Caution: Always wash your hands after touching an uncooked egg. It may contain harmful bacteria.
How can an emulsion be kept from separating? An emulsifying agent, such as an egg yolk, prevents an emulsion from separating. Prepare two mixtures as follows. One will contain an emulsifying agent, and one will not.
In a large bowl, combine 1 tablespoon (15 ml) of water, 1 egg yolk, and 1 tablespoon (15 ml) of liquid cooking oil. Beat the mixture thoroughly then pour it into a clear jar and label it ''WITH.''
Repeat the above procedure to combine 1 tablespoon (15 ml) of water and 1 tablespoon (15 ml) of liquid cooking oil Label the jar ''WITHOUT.''
Diagrams showing the contents of the jars after each action can be used as part of a project display.
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