Extraction. Ethyl alcohol is flammable. Avoid contact with used corn oil, which can stain clothing and hands. Gloves are recommended.

Transcription

1 Cautions Purpose Ethyl alcohol is flammable. Avoid contact with used corn oil, which can stain clothing and hands. Gloves are recommended. To use liquid-liquid extraction to purify a sample of corn oil. Introduction is commonly performed to purify valuable compounds in an academic lab and in chemical industry. Often, extractions are done with two immiscible liquids, usually organic and aqueous, or sometimes between two states of matter, usually gas and liquid. The success of an extraction is based on how well the target compound is soluble in one phase versus another phase. This success is measured by a distribution coefficient, which is the ratio of the concentration of the compound in one phase divided by the concentration of the compound in the other phase. X f = the concentration of compound f in the first phase Y f = the concentration of compound f in the second phase. The distribution coefficient is a property of both phases and the target compound and it allows us to predict how well a substance can be extracted. For example if the coefficient is much greater than 1, than we know that the compound is much more soluble in phase X than in phase Y. In our experiment today, we will be extracting xanthophylls from crude corn oil using an ethanol/water solution. Xanthophylls are natural pigments that occur in plants and usually have a yellow tint to them. Xanthophylls are an organic nonpolar compound with polar ends; an example is shown here: Because of this combination of polar and nonpolar properties, xanthophylls can be dissolved in both a nonpolar compound, like vegetable oil, and polar aqueous compounds, like the ethanol/water solution. One common xanthophyll is beta-carotene, which gives corn it s yellow color. When corn is ingested by chickens, the beta-carotene gives egg yolks and chicken fat their characteristic yellow color. To measure the amount of the xanthophylls in the aqueous phase, we will be using a spectrometer. As the concentration of xanthophylls in a sample increases, the intensity of the yellow color also increases. We will also be performing multiple extractions of the xanthophyll in order to model a continuous process found in industry. The process we will be modeling is countercurrent extraction, which is a method of multiple liquid-liquid extractions that allows substances with different distribution coefficients to be separated. In our 2 stage extraction, fresh oil will be mixed with alcohol that is already washed. A 2 stage extraction is diagrammed below. Revision F10 IB Page 1 of 7

2 Procedure 1. Obtain a spectrometer and cuvettes, turn on the instrument, and set the wavelength to 445 nm. 2. Obtain a 125 ml separatory funnel, ring stand with a support for the funnel, two 100 ml graduated cylinders, four 100 ml beakers, a 200 ml beaker, a 50 ml volumetric flask and a 400 ml beaker. 3. Obtain about 50 ml of crude corn oil in the 200 ml beaker 4. Obtain about 300 ml of 82% ethanol solution in the 400 ml beaker. 5. Take a sample of the ethanol solution and pour it in a cuvette; use this to blank (zero A/100%T) the instrument. 6. Combine 75.0 ml of the ethanol solution and 25.0 ml of the crude corn oil in the 125 ml separatory funnel. (Make sure the valve of the funnel is closed) 7. Put the stopper in the top of the funnel and shake the funnel 3 times. Place the funnel in the ring stand and allow to separate. The top will be the alcohol phase and the bottom will be the oil phase. 8. Open the bottom of the funnel and drain the oil phase into one of the 100 ml beakers and label it O1. Make sure you slowly pinch the valve back as the top phase starts to mix and close the valve when the oil is all out. 9. Drain the alcohol off into the graduated cylinder and label it A1. Record the volume of A Make a 1:10 dilution of the alcohol phase by using a 5 ml pipette to measure it out into a 50 ml volumetric flask. The dilution should be made with the original alcohol solution. 11. Measure the absorbance of the diluted solution and record the value. 12. Take the oil in O1 and return it to the separatory funnel along with 75 ml of the fresh ethanol solution and repeat step Drain the oil back into O1 relabeling it O21, noting the difference in color. 14. Drain the ethanol phase into a clean graduated cylinder labeling it A21. Record the volume of A Make a 1:10 dilution of the alcohol phase by transferring 5 ml A21 into a 50 ml volumetric flask. Dilute to the line with the original alcohol solution. 16. Measure the absorbance of the diluted A21 solution and record the value. 17. Take the solution in A1 and pour it into the separatory funnel along with 25 ml of fresh corn oil. Repeat step Drain the oil into a clean 100 ml beaker and label it O22. Record the color of the oil. 19. Drain the ethanol phase back in A1, relabeling it A22. Record the volume of A Make a 1:10 dilution of the alcohol phase by transferring 5 ml A22 into a 50 ml volumetric flask. Dilute to the line with the original alcohol solution. 21. Measure the absorbance of the diluted A22 solution and record the value. Waste Disposal Collect the used corn oil in the provided waste container. Alcohol solutions may be discarded in the sink. Clean-Up Rinse glassware that contained oil with a small amount of acetone then liberally wash all glassware with soap and water. Rinse once with deionized water. Revision F10 IB Page 2 of 7

3 Calculations Show all your work below or on a separate sheet of paper. Based on the absorbance measurements, calculate the concentration of xanthophylls in the ethanol solutions using the following equation: Concentration (g/l) = A (absorbance) x Calculate the concentration of xanthophylls in your extracted sample using the dilution equation, (Concentration) 1 V 1 = (Concentration) 2 V 2 Calculate the mass of xanthophylls recovered in each extraction by using the concentration and volume. Revision F10 IB Page 3 of 7

4 Data Sheet Name: Lab Partner: 1 st 2 nd Stage 1 Stage 1 Stage 2 Oil Sample O1 O21 O22 Color of Oil Alcohol Sample A1 A21 A22 Volume recovered (ml) Absorbance Diluted Xanthophyll Concentration (g/l) Undiluted Xanthophyll Concentration (g/l) Mass of xanthophylls extracted (g) Revision F10 IB Page 4 of 7

5 Post-lab Assignment Name: 1. Compare the difference in mass of xanthophylls recovered from each stage. What does this tell you about the effectiveness of your extractions? 2. How would the results be different if you used 100 ml of ethanol solution instead of 75 ml in step 6? 3. Describe the steps that would be involved in a three stage extraction process. Revision F10 IB Page 5 of 7

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7 Pre-lab Assignment Name: 1. When it comes to solubility, what is meant by like attracts to like? 2. What are some factors that affect the solubility of a molecule in different solutions? 3. Identify 2 examples of polar compounds. 4. Identify 2 examples of nonpolar compounds. Revision F10 IB Page 7 of 7