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What Do You Think?
One way to get different types of materials is to just mix them together. Lots of different things can happen when materials are mixed. Each kind of mixture has its own characteristics.
- Is it easier to separate milk from coffee or milk from a bowl of cereal? Record your ideas about this question in your Active Chemistry log. Be prepared to discuss your responses with your small group and the class.
Investigate
- Half-fill six large test tubes with water. Number the test tubes.
a) In your Active Chemistry log, prepare a table for your observations. You may wish to use a table similar to the one on the following page.
Activity 3 Solutions, Suspensions, and Colloids
GOALS
In this activity you will:
- Explore different ways that materials can be mixed together to make new materials.
- Test some materials to determine what kinds of mixtures they are.
- Determine why certain kinds of mixtures are manufactured for commercial use in particular situations.
Safety goggles and a lab apron are required for this activity. Wipe up spills immediately. Report any broken or cracked glassware to your teacher.
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Activity 3 Solutions, Suspensions, and Colloids
#1 water only
#2 0.5 g sugar
#3 drops of milk
No. Materials mixed Observations Observations with water before mixing after mixing Kind^ Filter
- Add the following materials to the test tubes: #1—nothing #2—0.5 g sugar #3—a few drops of milk #4—0.5 g CuSO 4 (copper sulfate) #5—2 mL olive oil #6—0.5 g soil a) Describe each material before mixing. 3. Stopper each test tube. Place your finger over the stopper and shake each for several minutes to make a mixture.
Observe each mixture.
- Consider the following characteristics of the mixtures:
- What is the appearance of each mixture after the vigorous mixing? Which ones have visible particles suspended in them? Which ones look totally uniform (homogeneous) throughout?
- Which mixtures separate (are heterogeneous) after sitting a few moments after vigorous mixing? Which remain mixed?
- Shine a laser pointer through each mixture. In which mixtures is the laser beam clearly visible? In which mixtures does it pass through with little effect?
- For each mixture place a small beaker below a funnel to catch the filtrate, as shown in the diagram on the next page. Pour the contents of each test tube into a funnel with filter paper. Which mixtures pass through? Which leave part behind on the filter paper?
water
Never look directly at a laser beam.
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Activity 3 Solutions, Suspensions, and Colloids
settle out over time.You could see the laser beam as it passed
through the mixture, and when you filtered the mixture, it all passed
through the filter paper.This kind of mixture is a colloid. In colloids,
the dispersed particles are larger than those in solution and may
be visible on close inspection with a microscope.The particles will
also stay suspended indefinitely. All parts of the colloid will pass
through a filter.When light passes through a colloid it is scattered
and you can see where the light beam passes through.This is known
as the Tyndall Effect.
When you added soil to water, you created a suspension.
Suspensions have the largest of all the dispersed particles.The
particles are visible to the eye and will settle out in time.The
suspended particles can be separated by filtration.The mixture is said
to be heberageous. A light beam shining through a suspension may be
scattered, but the suspension is definitely not transparent.
Chem Words colloid: a mixture containing particles larger than the solute but small enough to remain suspended in the continuous phase of another component. This is also called a colloidal dispersion. Tyndall Effect: the scattering of a light beam as it passes through a colloid. suspension: heterogeneous mixture that contains fine solid or liquid particles in a fluid that will settle out spontaneously. By shaking the container they will again be dispersed throughout the fluid.
Checking Up
- In your own words describe how you would distinguish among a solution, a colloid, and a suspension.
- What is the Tyndall Effect?
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Reflecting on the Activity and the Challenge
In this activity you made mixtures with solid or liquid solutes and water as the solvent. The same basic principles apply regardless of the states of matter involved. For example, it is possible to have solid solutions. Metal alloys such as brass or bronze are such solutions. Fog, smoke, and clouds are mixtures that show the Tyndall Effect. A common stage effect is to produce smoke or fog
to give an eerie setting. Many movies have used the Tyndall Effect to show the path of laser beams or flashlights. One easy way to produce this effect is to use a spray bottle of water to mist the air in a darkened room (problem with allergies/asthma). When a flashlight or laser pointer is directed through the mist, it shows up nicely, thanks to the Tyndall Effect.
- Classify each of the following as a suspension, colloid, or solution. Explain your reasoning. (Hint: In some cases more than one answer may be possible.) a) A mixture is poured through a filter, and the entire mixture passes through.
b) A mixture is left to stand for a while and small particles settle out. c) When viewed under a microscope, small particles are visible in the mixture.
d) A beam of light passed through the mixture is scattered.
e) The mixture is blue and transparent.
- Suggest a method by which you could separate the various materials in each of the following mixtures: a) solutions b) colloids c) suspensions 3. On some days it is possible to see rays of light from the Sun distinctly coming through breaks in clouds. What in the atmosphere might account for this difference? 4. The term homogeneous means uniform or the same throughout. Heterogeneous means that different parts of the mixture are clearly visible. Classify each of the mixtures in this activity as homogeneous or heterogeneous. 5. Look in your kitchen at home and choose five products. Make your best guess as to the type of mixture they represent. Elaborate on the evidence that you used to classify the products into the respective category. Explain what would happen to each product that you have chosen if it were in a different kind of mixture. For example, milk would settle if it was a suspension instead of a colloid.
