Is the Green Coloring in Leaves a Single Substance or a Mixture of ...

Name:______________ Date:__________ Per:________Is the Green Coloring in Leaves a Single Substance or aMixture of Different Substances?INTRODUCTIONThe green leaf is the chief site of the process of photosynthesis. The plant’s pigments,which give the plant its color, help to capture light energy. The plant can then use this energy tomake its own food. Since photosynthesis is so important to the world’s food supply, it isunderstandable that biologists and biochemists want to know all they can about the greensubstance in leaves.In this investigation you will use a technique called paper chromatography to determinewhether the green substance is a single substance or a mixture of substances. Paperchromatography is a technique that separates mixtures of substances into their separatecomponents.MATERIALSspinach leaf coin cork stopper with hooksolvent ruler flasktest tube chromatography paper pencilPROCEDURE:WEAR SAFETY GLASSES1. Obtain a test tube with a tight-fitting cork or stopper.2. Obtain a chromatography paper strip. Cut the strip so that the strip will fit into yourtest tube. When you put your paper strip into the test tube, the strip should not be“scrunched”. With a pencil, not a pen, draw a line about 2 to 3 cm from the lower end ofthe strip.3. Now, you are ready to make your chromatogram. Take your spinach leaf and place itupside down on your strip. Using a coin, gently roll it across the spinach leaf along thepencil line on your paper strip. If you pressed hard enough to damage the leaf you shouldnow see a green line right on top of your pencil line. Repeat this process on top of thepencil line using other areas of the leaf until you get a dark green line. You do not want agreen splotch. Be careful not to press too hard or you may rip your paper strip and haveto start over. You may blow on the line or wave the paper in the air to speed the drying.It must be dry.corktest tubepaper stripdark line of pigment on the paper stripsolvent in the bottom of the test tube

4. Put solvent into your test tube so it only touches the bottom of the paper strip. Placethe paper strip into the test tube and keep it straight and in place with the hook that isinserted at the bottom of the cork stopper. The pigment line must remain well above theliquid solvent. Do not let the solvent touch the pigment line. The bottom of the stripmust be in the solvent.5. Let the tube stand upright and motionless in the flask until the solvent moves up thepaper to the top—about 10 minutes. Check your chromatogram every few minutes to besure that the solvent does not go beyond the top of the paper strip. When the solventhas reached the top, immediately remove the paper strip from the test tube. Let thepaper strip dry.6. Notice the faint bands of color. Spinach leaves contain the following pigments:carotene (yellow-orange)xanthophyll (pale yellow)chlorophyll a (bright green)chlorophyll b (olive green)7. Using a pencil, lightly circle each band of color on your chromatogram. Tape thestrip vertically to the back of the discussion questions. Compare your results tothose of other students at your lab table.8. Leaves of other plants may not have all of these colors. Some leaves may have additionalpigments.9. Complete the discussion questions.

Name: Date: Period:CHROMATOGRAPHY LABTape your labeled strip below!!!!!DISCUSSION QUESTIONS1. Is the green pigment in leaves a single compound or a mixture of several compounds?__________________2. Explain what you saw on the chromatogram.3. Chlorophyll is green. Is all of the pigment in spinach leaves chlorophyll? _________Explain.4. In the spring and summer many leaves of trees are green. Explain why you might seedifferent colors in those same leaves in the fall of the year before the leaves die anddrop off of the trees.4. How many color bands can you see on your chromatogram? __________ How does thiscompare with what other groups found?5. If special tests and instruments identified a certain band of color on your chromatogramas chlorophyll a, how could you identify chlorophyll a on someone else’s chromatogramwithout using those tests and instruments? (You need 2 answers here.)6. Carrots contain a pigment that gives them their distinct color. Is there any indicationthat the leaves you tested may have some of this same pigment? _____________Explain.