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Main Curriculum Tie:
Background For Teachers:
This activity will help students understand the differences between color mixing and color change due to a chemical reaction as they “get back” the colors they mixed together using chromatography. Chromatography is a method used to separate the different ingredients of a mixture. It was first used by Russian botanist Mikhail Tsvet to separate the pigments that make up plant dyes. It is now used to determine the ingredients that make up flavors or scents, to analyze the components of pollutants, to find traces of drugs in urine, and to separate blood proteins to identify various species of animals. Chromatography is also commonly used in police labs to determine unknown substances found at crime scenes.
There are many different types of chromatography, but all of them involve a gas or a liquid (the water in this activity) flowing through a stationary substance (the paper towel). Because the physical and chemical make-up of the pigments used to make colors vary, the rate and distance at which they travel along the paper towel varies, causing the colors to separate out.
This activity is written as a hands-on activity for cooperative teams. However, the color mixing (steps 1-5) could be done as a teacher demonstration using petri dishes on an overhead
projector. Teams should complete the color separation (chromatography).
Intended Learning Outcomes:
Invitation to Learn:
*Sodium polyacrylate is an essentially harmless substance that was developed by NASA to use in astronaut diapers. Sodium polyacylate can be obtained from most chemical suppliers.
Part 1 Color Mixing:
After the teams have completed the above procedures, lead a discussion about the color mixing activity. Have students share what colors each mixture made. Record their responses on the board. Ask: “Is color mixing a physical change or a chemical reaction? What evidence supports your answer?” You may have students supporting both choices. Some students may feel, since there was a color change, that there was a chemical reaction. Accept all answers and record the responses on the board. Tell the students that the next part of the activity will help answer the question. Ask: “Can the substances in a chemical reaction be returned to their original states?” (No)“ Can the substances combined in a physical change (mixture) be separated out?” (Yes)
Have the teams complete the following procedures:
Part 2 Chromatography:
At this point lead a discussion about what the students have observed. Share the information from the “Background” section above. Make sure students understand that mixing colors just changes the physical property of color and that usually the colors can be separated out. This shows that only a physical change has occurred. When there is a color change during a chemical reaction, there is a change at the molecular level and new substances are formed.
Use this rubric to assess your students ' performances:
Student 's Name ____________________________________
Created Date :