Investigating Chromatography: selecting variables
Summary
In this classroom lab, students will design an experiment to separate colors of various water-based pens in order to learn about mixtures and solutions. Students will determine a variable to test and complete a lab report.
CollapseLearning Goals
The students will demonstrate observation skills as they complete a lab report.
Students will develop a question and design an experiment with one variable.
Student will investigate a physical change.
Vocabulary:
mixture, solution, solute, solvent, pigment, variable, chromatography, density
Students will develop a question and design an experiment with one variable.
Student will investigate a physical change.
Vocabulary:
mixture, solution, solute, solvent, pigment, variable, chromatography, density
Context for Use
This is a short classroom lab that could be a small group or individual activity. It could be used as part of a mixtures and solutions investigation or to teach the practice of science.
Description and Teaching Materials
In my class this activity would follow an investigation where students would attempt to clean dirty water. I would then provide background information on mixtures and solution, perhaps read part of a Foss booklet. We could discuss physical and chemical changes, as well. I would introduce the vocabulary (mixture, solution, solute, solvent, pigment, variable, chromatography, density).
The word chromatography comes from the combination of two Greek words: "chroma' or color and "graph" to write.
Materials:
- 2 - 3 sheets of coffee filter paper per group
- 2 - 3 Popsicle sticks or a pencils per group
- 2 – 3 Clear containers per group
- Pencil and lab sheet
- ruler
- several types of water based pens and a few that are not (Visa Vis work well)
- solution (enough to cover ½ inch of the bottom of the containers)
o 1% salt solution (1/8 teaspoon of salt to 3 cups of water)
o alcohol
o white vinegar
Preparation: Cut the coffee filters into strips.
Introduction: Ask if anyone has ever spilled water on their homework or a letter and had the ink run? Hold up an example prepared earlier. What was happening?
I would do a demo of chromatography using different colors of regular markers and ask the following questions:
- What do you notice?
- What do you think is happening?
- What is the solute and what is the solution?
- What is the variable in this experiment?
- What other variables could you use? Discuss variables
I would then assign Chromatography lab (assignment sheet attached) and review the instructions.
I would debrief and share results.
Chromatography is used to separate ink into the chemicals that are used to make it, each having a different color. Why does the solution climb the paper? It is a process called capillary action. The color spots climb up the filter paper along with the solution they separate into different bands. Some dyes or colors are more soluble and travel with the solution longer. The density of the pigment makes a difference – lighter dyes move higher.
The assessment will be lab report. Student Handout for Chromatography Investigation (Microsoft Word 2007 (.docx) 14kB Aug3 09)
The word chromatography comes from the combination of two Greek words: "chroma' or color and "graph" to write.
Materials:
- 2 - 3 sheets of coffee filter paper per group
- 2 - 3 Popsicle sticks or a pencils per group
- 2 – 3 Clear containers per group
- Pencil and lab sheet
- ruler
- several types of water based pens and a few that are not (Visa Vis work well)
- solution (enough to cover ½ inch of the bottom of the containers)
o 1% salt solution (1/8 teaspoon of salt to 3 cups of water)
o alcohol
o white vinegar
Preparation: Cut the coffee filters into strips.
Introduction: Ask if anyone has ever spilled water on their homework or a letter and had the ink run? Hold up an example prepared earlier. What was happening?
I would do a demo of chromatography using different colors of regular markers and ask the following questions:
- What do you notice?
- What do you think is happening?
- What is the solute and what is the solution?
- What is the variable in this experiment?
- What other variables could you use? Discuss variables
I would then assign Chromatography lab (assignment sheet attached) and review the instructions.
I would debrief and share results.
Chromatography is used to separate ink into the chemicals that are used to make it, each having a different color. Why does the solution climb the paper? It is a process called capillary action. The color spots climb up the filter paper along with the solution they separate into different bands. Some dyes or colors are more soluble and travel with the solution longer. The density of the pigment makes a difference – lighter dyes move higher.
The assessment will be lab report. Student Handout for Chromatography Investigation (Microsoft Word 2007 (.docx) 14kB Aug3 09)
Teaching Notes and Tips
I have not used this activity in my classroom. It would be difficult to draw the results as the dyes climb to the top of the strip and the separations are not in clear lines or regions. Some of the pens will not separate. Acetone is a good solution for the non-water soluble inks. Additionally one activity on the web suggested taking the dye off candy -like M&Ms. I found this to be tricky and messy and time consuming. Kool-aid or food coloring would work. It takes a while (15 minutes) for the ink to climb, so I plan to either have another activity or some reading, or go back to it later. It could be the next day.
Assessment
This activity will be assessed by the acccurate completion of a lab report, including a research question, documentation and an explanation.
Standards
5.1.1.2.3 conduct and critique a controlled experiment
6.1.3.4.1 determine and use procedures to describe a change
6.2.1.2.1 identify evidence of a physical change
6.1.3.4.1 determine and use procedures to describe a change
6.2.1.2.1 identify evidence of a physical change