Lab 5.3 Separating Solutions- Chromatography

LAB 5.3 SEPARATING SOLUTIONS- CHROMATOGRAPHY

BACKGROUND:

Different colors can be attained by mixing various pigments together to achieve the desired result. A mixture of pigments was added to water to produce a green solution. We have already determined that water can be separated from a solution by boiling, leaving behind all the solutes. We have not yet determined a method to separate two solutes from one another in the same solution. In this lab you will use chromatography to separate the pigments (solutes).

PURPOSE: To determine how many different kinds of particles are in green food coloring. To explain the separation of color using a particle model.

PRE-LAB QUESTIONS:

1. Is green food coloring a solution? Explain.

2. What are the solutes in food coloring?

PROCEDURES:

A. Add water to a flask so that only about 1 cm of water covers the bottom of the flask.

B. Obtain a piece of chromatography paper and write your name at the top in pencil. Use a pencil to draw a line across the width of the paper about 2 cm from the bottom edge of the paper. Refer to Fig.1.

C. Place a green dot of food coloring on the pencil line. Sketch your paper before lowering it into the water.

D. What will happen to the green dot when the paper is lowered into the flask? Write a sentence to record your prediction.

E. Lower the paper into the flask. Be sure the green dot is above the water line. A toothpick can be inserted through the top of the paper to allow the paper to be suspended down into the flask.

F. Leave the paper in the water until the water has moved at least half way up the paper.

G. Sketch your paper just before removing it from the flask. Label your sketch to indicate the colors.

INTERPRETATIONS:

1. How many different kinds of dye particles are in green dye? Describe the evidence.

2. Identify the solvent used in this chromatography lab. Identify the solute.

3. Use particle attractions to explain what causes the water to move up the paper.

4. Use particle attractions to explain what causes the dye to move up the paper.

5. Use particle attractions to explain why the pencil mark does not move up the paper.

6. Investigating why the colors separate.

a) Give two hypotheses to explain what causes one color to move faster than another.

b) Describe experiments to test each hypothesis.

7. a) Describe the setup and results of the class experiments.

b) Which hypotheses should be rejected based upon the results? Explain.

c) What appears to be the best explanation for the separation of colors? Explain.

CONCLUSION:

To help you structure your conclusion for Lab 5.3, think about the following questions as you write.

Paragraph 1: Introduction

• Describe, briefly, the chromatography process and the results that you obtained.
• Explain the two types of particle attraction involved in chromatography
• Introduce the question asked that led to the hypotheses and class experiments

Paragraph 2: The hypothesis that was supported

• Make a claim about which hypothesis was supported by the class experiments
• Describe the evidence that supports the claim
• Write linking sentences to explain how the evidence supports the claim

Paragraph 3: One hypothesis that was rejected

• Make a claim about one of the hypotheses that was rejected by the class experiments
• Describe evidence that led to rejecting this hypothesis
• Write linking sentences to explain how the evidence justifies rejecting this hypothesis