Mixture Separation Challenge

Mixture Separation Challenge
Item #MIX-100

Best used for 24 students working in pairs.

Reusable materials included in this kit:
• Mixture of four plastic polymers
• 50 small plastic cups
• 12 plastic spoons

Required, but not included:
• NaCl, common table salt (Kosher salt gives a clear solution.)
• Paper towels

Optional:
• 250 mL beakers, 1 per group

Purpose
This is an elegant demonstration of the property of density, heterogenous and homogenous solutions, and percent composition.

Directions
Each type of plastic polymer included in this kit has a different density, making it possible to separate each type using water and salt. First, give each group of students a small sample of the mixture, making certain that each group receives some of each type of plastic.

Instruct students to observe and weigh the mixture and describe whether it is homogenous (uniform throughout the mixture) or heterogenous (inconsistent throughout the mixture). Since color and shape vary throughout the mixture, the plastics pieces tend to make a heterogenous mixture.

Have students place the mixture in their plastic cup or beaker and add water. This will cause one type of plastic to float and some to sink. Have students gently tap the pieces floating at the top – some pieces will be floating due to air bubbles or surface tension. Eventually only one type of plastic will be left floating. Students can then spoon the plastic pieces off the surface of the water, dry the plastic, and weigh it.

Next, have students slowly add salt to the mixture, while stirring. Eventually, another type of plastic will float to the top. Again, surface tension or air bubbles may cause other plastics to rise, and students should gently tap the floating plastics. The floating plastics that remain should be spooned off, dried, and weighed.

As more salt is added, the third type of plastic will float and can be spooned off, dried, and weighed, leaving the fourth and final plastic resting at the bottom of the beaker. Students can then dry this fourth plastic and weigh it.

After students weigh each sample they can calculate the percent composition of their mixture.

Compare the different percent compositions from the class. Explain that since each group has a different percent composition, this shows the mixture is heterogenous. If the mixture were homogenous and uniform, each group would have an identical percent composition.

Safety
Standard safety procedure should be observed at all times. Students should wear safety goggles and use caution when working with glassware. Do not attempt to separate the mixture with heat or other chemicals.

Activity Sheets

Names:________________________________________________

Determine the mass of your entire sample by weighing it.
Your mixture weighs: ________________________

In this experiment you will separate a mixture of four different types of plastic. You will learn about homogenous and heterogenous mixtures. A homogenous mixture is uniform, which means that every part of the mixture appears the same. A heterogenous mixture is not uniform, and different samples of the mixture will have different properties.

Is your mixture homogenous or heterogenous? __________________________

Place your mixture in a cup or beaker and add water. Stir the entire mixture. Some pieces of plastic may float to the top. Some of these pieces may be floating because of air bubbles or surface tension. Firmly tap all of the pieces of plastic to make certain pieces with air bubbles sink.

What do you observe? How many types of plastic are floating on top of the water? This is because the plastic floating has a lighter density than water. Density is a measure of mass per volume.

Spoon away all of the floating plastic and dry it in a paper towel. Weigh the plastic on a balance.

Plastic #1 weighs: _______________________________

Next, add a spoonful of salt to your beaker or cup and stir. Continue adding salt one spoonful at a time and stirring until you notice another type of plastic float to the surface. Be sure to tap the plastics to sink any that have air bubbles. Spoon the floating plastic out of the water and dry it in a paper towel. Weigh the plastic on a balance.

Plastic #2 weighs: _______________________________

Why did plastic #2 float after adding salt?

_______________________________________________________________

Continue to add salt and stir your water. Eventually, the third plastic will rise to the surface. Spoon out this plastic, dry it in a paper towel, and weigh it.

Plastic #3 weighs: ________________________________

The final plastic will be resting at the bottom of your beaker or cup. Carefully pour out the water and collect the final plastic. Dry it in a paper towel and weigh it.

Plastic #4 weighs: ________________________________

The last step in this experiment is to determine the percent composition of your mixture. Percent composition will describe the amount of each kind of plastic in your mixture. To find the percent composition, divide the weight of a plastic by the weight of the entire sample, then multiply your answer by 100.

Percent Composition of Each Plastic in the Mixture

The Percent of Plastic #1 in the mixture is: _________________________%

The Percent of Plastic #2 in the mixture is: _________________________%

The Percent of Plastic #3 in the mixture is: _________________________%

The Percent of Plastic #4 in the mixture is: _________________________%

If you add each percent composition together, what number do you get? _________

Did everyone in your class have the same percent compositions?

_____________________________________________________________

If everyone had the same percent compositions, then the mixture would be homogenous. However, if everyone had different percent compositions, this indicates that your mixture may have been heterogenous.

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