Teacher Notes
|
---|
Teacher Notes![]() Column ChromatographyStudent Laboratory KitMaterials Included In Kit
Acetone, CH3COCH3, 500 mL
Aluminum oxide, alumina, Al2O3, 75 g Hexane, C6H4, 1 L Chromatography columns, 15 Pipets, thin-stem, 90 Sand, 30 g Spinach powder, 15 g Tomato paste, 6-oz can Additional Materials Required
Balance, 0.1-g precision (shared)
Beakers, 50-mL, 3* Beaker, 250-mL* Can opener† Clamp* Erlenmeyer flask, 250-mL† Erlenmeyer flask, 500-mL† Graduated cylinder, 10-mL* Graduated cylinder, 100-mL† Spatula* Stirring rod† Stoppers, 4 (to fit flask)† Stoppers, size 0, 3–4* Support stand* Test tubes, 13 x 100 mm, 3–4* Test tube rack* Weighing dish small* *for each lab group †for Prelab Preparation. Prelab Preparation
Safety PrecautionsAcetone and hexane are flammable liquids and dangerous fire risks. Acetone is also slightly toxic by ingestion and inhalation. Hexanes are a respiratory irritant. Perform this experiment only in a well-ventilated lab. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information. DisposalPlease consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Save any remaining acetone or hexane for future use. Dispose of the dry spinach powder, tomato paste, sand and aluminum oxide in the regular trash according to Flinn Suggested Disposal Method #26a. Lab Hints
Correlation to Next Generation Science Standards (NGSS)†Science & Engineering PracticesDeveloping and using modelsPlanning and carrying out investigations Disciplinary Core IdeasHS-PS1.A: Structure and Properties of MatterHS-PS1.B: Chemical Reactions HS-LS1.C: Organization for Matter and Energy Flow in Organisms HS-ETS1.C: Optimizing the Design Solution HS-PS3.D: Energy in Chemical Processes HS-PS4.A: Wave Properties Crosscutting ConceptsEnergy and matterCause and effect Systems and system models Structure and function Patterns Performance ExpectationsHS-LS1-5: Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy. Answers to Prelab Questions
Sample DataExtract:___Spinach Extract___ {12946_Data_Table_1}
Extract:___Tomato Extract___ {12946_Data_Table_2}
Answers to Questions
ReferencesBraithwaite, A.; Smith, F. J. Chromatographic Methods, 4th ed.; Chapman & Hall: New York, 1990; p 29, Chapter 4. Recommended Products |
Student Pages
|
---|
Student Pages![]() Column ChromatographyIntroductionColumn chromatography is a popular analytical technique used to separate, isolate and purify organic and biological compounds. In this activity, pigments from tomato paste and spinach powder will be extracted and separated using column chromatography. Concepts
BackgroundChromatography is one of the most useful methods to separate mixtures. Chromatography is defined as the separation of a mixture of two or more different compounds or ions by distribution between two phases. The first phase is a stationary phase known as the adsorbent, and the second phase is a mobile or traveling phase called the eluent. {12946_Background_Figure_1}
{12946_Background_Figure_2}
Chlorophylls are green pigments found in the chloroplasts of green plants and algae. Xanthophyll is a yellow pigment also found in plant leaves, some plants and algae. Both spinach and tomatoes also contain the yellow-orange pigment β-carotene. Lycopene is a red pigment that gives tomatoes their characteristic red color. Xanthophyll, lycopene and β-carotene are carotenoid pigments. The color of these pigments is important because it is possible to see them separate and exit the chromatography column individually, based on their color. The colors of the pigments are due to their chemical structures. Each pigment molecule contains conjugated double bonds—alternating single and double bonds. Compounds that have eight or more conjugated double bonds absorb light in the visible region of the spectrum, hence we see their color. Chlorophyll a and b, xanthophyll, β-carotene, and lycopene are different colors because their absorption maxima occur at different wavelengths of visible light. This color difference is due to subtle differences in the molecular structure of each pigment. In each case, the color the pigment absorbs is not the color it appears. Instead, the color the pigment appears is the same as the complement of the color of light it absorbs. These complementary colors are the colors the human eye perceives. Table 1lists the absorption maxima for each pigment, the colors of light each pigment absorbs, and the perceived color of each pigment.
{12946_Background_Table_1}
The absorption maxima and pigment colors can also be displayed graphically in Figures 2 and 3 by plotting the absorbance of visible light as a function of wavelength. Figure 3 shows the absorption spectra of visible light by plant pigments. Chlorophyll pigments in spinach leaves absorb primarily at the red and blue ends of the spectrum, so that green light is reflected or observed. Hence, spinach appears green.
{12946_Background_Figure_3_Absorption of visible light by pigments in spinach}
Figure 4 shows tomato pigments absorb light in the blue and green regions of the spectrum. Therefore, red is reflected and tomatoes appear red.
{12946_Background_Figure_4_Absorption of visible light by tomato pigments}
Experiment OverviewEach lab group will carry out a column chromatography experiment on either spinach powder or tomato paste. The pigments will be separated by elution with different solvents and collected in separate test tubes. Materials
Acetone, CH3COCH3, 10 mL
Aluminum oxide, Al2O3, 2.0 g Hexane, C6H4, 10 mL Hexane-acetone, 50/50 mixture, 10 mL Hexane-acetone, 80/20 mixture, 10 mL Sand, 0.5 g Spinach powder, 0.5 g Tomato paste, 1 g Balance, 0.1-g precision (shared) Beaker, 50-mL Beaker, 250-mL Chromatography column Clamp Graduated cylinder, 10-mL Pipets, thin-stem, 3 Spatula Stirring rod Stoppers, size 0, 2–4 Support stand Test tubes, 13 x 100mm, 2–4 Test tube rack Weighing dish, small Prelab Questions
Safety PrecautionsAcetone and hexane are flammable liquids and dangerous fire risks. Acetone is also slightly toxic by ingestion and inhalation. Hexanes are a respiratory irritant. Perform this experiment only in a well-ventilated lab. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.. ProcedurePreparation of the Chromatography Column (all groups)
Student Worksheet PDF |