CHEM 14CL Summer 05NOTE: Make sure that you look for organization of ideas and not just a copy of the procedure in boxes.Pre-lab Report Guideline for Experiment 7(a) ContinuePOST-LAB Report Guidelines for EXTRACTION AND PURIFICATION OF CAFFEINE FROM TEA LEAVES EXPERIMENTThis is an individual report(A) Abstract(B) Data AnalysisCHEM 14CL Summer 05 7(A) - Extraction and Purification of Caffeine from Tea Leaves Procedures for experiment 7(A) - see p.76 - 80 (lab manual) Pre-lab Report Guidelines for Experiment 7(A) NOTE that ONLY parts 1 and 2 are DUE on Wednesday. 7/6 and Part 3 1(Study questions) is DUE on Friday, 7/8 Part 1. Introduction – list the goal(s) of the experiment and any experimental techniques that will be used during the experiment for purification and/ or identification. Part 2. Prepare a flow chart of procedures AND show the location of the caffeine throughout each step of the experiment in the flow chart. Make sure you also REFERENCE the procedures. NOTE: Make sure that you look for organization of ideas and not just a copy of the procedure in boxes. Part 3. Study Questions: Complete the following questions. (MUST SHOW ALL WORK FOR FULL CREDIT). Note: Kp is equivalent to α (see lecture guide for definition). (a) You wish to extract an organic compound from an aqueous phase into an organic layer (three to six extractions on a macroscale). With regard to minizing the number of transfer steps, would it be better to use an organic solvent that is heavier or lighter than water? Explain. (b) A compound distributes between water (phase 1) and benzene (phase 2) with Kp = 2.7. If 1.0g of the compound were dissolved in 100mL of water, how much compound THREE 10-mL portions of benzene could extract?7(A) - Extraction and Purification of Caffeine from Tea Leaves Pre-lab Report Guideline for Experiment 7(a) Continue Study Questions Continue: (c) If the value of kp is 0.5 for the distribution of a compound between pentane (phase 1) and water (phase 2), and equal volumes of the two solvents were used, how many extractions of the aqueous layer will be required to recover at least 90% of the compound? (d) Calculate the % of a compound that can be removed from the liquid phase 1 by using ONE to Four extractions with a liquid phase 2. Assume that kp = 2 and the volume of phase 2 equals 50% that of phase 1. (e) A slightly polar organic compound distributes between diethyl ether and water with a partition coefficient of 3 (in favor of the ether). What simple method can be used to increase the partition coefficient? Explain.POST-LAB Report Guidelines for EXTRACTION AND PURIFICATION OF CAFFEINE FROM TEA LEAVES EXPERIMENT This is an individual report (A) Abstract Outline the objective of the experiment as well as record any technique that you used to isolate and analyze the caffeine product. (B) Data Analysis (1) Record all observations. (2) Use equations to help explain any chemical reactions. or explain the phenomenon (physical changes) behind each of your other observations. (3) Calculate the % yield of crude caffeine that you recovered. (4) Mass Spectrum of caffeine: (i) identify the base peak. (ii) identify the molecular ion peak. (iii) is the molecular ion peak the same as the base peak in the spectrum? Note: that you will learn about the concepts in mass spectroscopy later this quarter. Just use the following definitions to answer the questions related to the mass spectrum of your caffeine products. Base peak is the signal on the mass spectrum that has the highest intensity or most intense peak in the spectrum Molecular ion peak is used to determin the molecular weight of the compound (just look for the a signal that gives you the molecular weight of caffeine) (5) UV Spectrum of caffeineA: Calculate the molar extinction coefficient (ε) for caffeine. Show all your work. Note: Assume the diameter of the cell holder to be 1 cm. (6) Calculate the Rf values of BOTH the pure caffeine and the crude caffeine. Show all your work. Note: Read pages 153-162 in Mohrig (Techniques on Organic Chemistry) about the concepts in Thin Layer Chromatography (TLC). Pay special attention to pages 154-155 on how to find Rf value and what it means. Concepts behind TLC will be discussed later on in the quarter.(C) Conclusion (i) Compare your % caffeine value to the reported value of about 2-4% caffeine content in tea leaves. Explain what may cause the % to be differed (i.e. where the loss of caffeine may come from during the experiments). (ii) (ii) Compare experimental IR spectrum to literature IR spectrum (provided with the experiment 7(B) worksheets). What can you conclude about the purity of your product? Note: If you don’t have the literature caffeine IR spectrum, go to the following web site to download the IR spectrum: http://webbook.nist.gov/chemistry/ Do a NAME search on caffeine and there should be a hyperlink for the gas phase IR spectrum of caffeine. (iii) Interpretation of caffeine product composition and purity from TLC results. Explain all your reasoning. NOTE: Before answering part (iii), refer to the notes on TLC listed on the previous page of this guideline. Attach ALL the spectra & the experimental TLC plate with your post-lab
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