Chromatography

1. Chromatography Spring 2019 Vanderbilt Student Volunteers for Science

2. Important!!! • Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit! • We recommend that you work through the kit with your team prior to going into the classroom. • This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.

3. I. Lesson Set-Up • Two VSVS members should do the set ups while a third VSVS member does the demonstration in Part II. • Remaining members will attach the chromatography papers that are already marked with the green pen to the sticks (see instructions below on how to do this). • Hold the paper strip so that the top edge of the paper is even with the top edge of the wooden stick. • Tear a small piece of tape and tape the paper strip to the wooden stick so that the tape goes around the stick and is taped to both the front and the back of the paper strip. • Set-up for Part III – SEPARATING COLORS - add about 30 mL of water to enough 16-oz cups for the class plus five for the demonstration in part II • While one team member starts Part II, another should write the following vocabulary words on the board. chromatography, chromatography, capillary action, forensic chromatography

4. 1. What is a Mixture? • Show students the bag of mixed balls. • Explain that each differently colored ball represents an element or compound. • The balls are not connected it is a mixture • There are 2 types of mixtures • Heterogenoeous • Homogeneous

5. 1A. Using the Magnetic Properties of Iron to Separate a Heterogeneous Mixture? • Show students a jar of sand. Why is it a Mixture? • Explain that sand contains shells, fossils, and organic matter. Sometimes it also contains an iron mineral that is magnetic • Ask them how could the iron be separated from the sand? • Iron is magnetic, sand is not • The VSVS team will demonstrate this test by removing the cow magnet from the jar. Show the students the particles collected by the magnet. • Explain the commercial use of cow magnets.

6. IB. Making a Homogeneous Mixture • Hold the jars containing the blue and yellow liquids up so the students can see them. • Ask the students: What color do you get when you mix blue and yellow? • Ask: "What will happen if you combine the 2 liquids? Accept responses. • Pour the blue liquid the yellow liquid together and show students that the mixing of the blue and yellow liquids makes a green liquid. • Ask students: Is this a homogeneous mixture? Why? The blue and yellow liquids cannot be seen anymore. • Did a chemical change happen? Or a physical change? (Physical). • Tell students that what we want to discover is a way to separate mixtures of colors and other mixtures of chemicals.

7. II. Using Chromatography to Separate a Homogeneous Mixture (using a green pen). • Show the students the green pen and tell them that the green is amixtureof blue and yellow inks. • Give each PAIR a chromatographic strip already attached to the stick, with the green line already drawn . • Take one of the 16 oz cups that contains 30 mL of water and gently place the stick across the16 oz. cup so the stick and paper will not fall into the cup. The strip should hang free in the center of the cup without touching the sides. • Make sure the green line is NOT in the water. • Explain capillary action (refer to manual).

8. III. Forensic Chromatography • Provide the crime scenario in the manual to students and tell them they will use chromatography to determine "Whodunit”!

9. III. Forensic Chromatography(cont.) • Distribute the following new materials to each PAIR: • 1 labeled suspect pen (PC, PS, JF, or MM) • 1 piece of chromatography paper • Distribute the suspect pens evenly so that approximately the same number of students have each type of pen. • Have students set up the chromatography paper as done before. Students may need help. • Tell each student to mark the top of the chromatography paper near the stick with the initials on their pen (PC, PS, JF, or MM). Hold up a stick with a piece of chromatography paper taped to it to make sure they mark the top near the stick. • Have students place their strips in the cups containing water as before. • Wait about five or six minutes for development of the chromatogram. • Remove the chromatogram and place it on a sheet of paper towel.

10. III. Who is the Guilty Person? • After the chromatograms are finished, distribute the 16 laminated chromatograms prepared from the guilty person 1 per pair) and ask them to compare their chromatograms with the chromatogram prepared from the guilty person’s pen (made from the ransom note) and identify which pen matches the results from the ransom note. • Ask, Who is the guilty person? (PC - Pam Chromatogram) • See manual for discussion and review questions.

11. IV Review • 1. Why does water move up the paper strip? Answer: capillary action • 2. In the separation of the green ink, the blue pigment moves higher (faster) than yellow pigment. Why? Answer: The speed of movement of a component of a mixture, in this case colors, depends on its relative solubility in the solvent (water) and its relative strength of attachment (absorption) to the paper. The blue pigment is more soluble (more attracted to water than to the paper) and less absorbent (less attracted to the paper) so it moves faster up the paper strip.