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Green Chemistry Workshop #4: Analytical Chemistry II

Green Chemistry Workshop #4: Analytical Chemistry II. US – Thai Distance Learning Program February 24, 2010 Professor Kenneth M. Doxsee University of Oregon. The Principles of Green Chemistry. Prevention Atom Economy Less Hazardous Synthesis Designing Safer Chemicals

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Green Chemistry Workshop #4: Analytical Chemistry II

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  1. Green Chemistry Workshop #4:Analytical Chemistry II US – Thai Distance Learning Program February 24, 2010 Professor Kenneth M. Doxsee University of Oregon

  2. The Principles of Green Chemistry • Prevention • Atom Economy • Less Hazardous Synthesis • Designing Safer Chemicals • Safer Solvents and Auxiliaries • Design for Energy Efficiency • Renewable Feedstocks • Reduce Derivatives • Catalysis • Design for Degradation • Real-time Analysis • Inherently Safer Chemistry

  3. Cementation Experiment from Session 3

  4. Determination of Acetylsalicylic Acid in an Aspirin Tablet Premise • Acid-base titration can be used to determine the quantity of acetylsalicylic acid. Chemical Concepts • Acid-base chemistry; titration; volumetric analysis. Aspirin image: http://www.bayerhealthcare.com/html/images/upload/presse/aspirin_tablette_205.jpg

  5. Background • Aspirin is derived from salicylic acid, originally obtained from the bark of a willow tree. • Commercial aspirin tablets contain acetylsalicylic acid as the active ingredient. • Typical tablets also contains “binders” and “fillers” such as corn starch or cellulose. Tree image: http://www.janiceboling.com/herbs/images/willow.jpg

  6. Reaction Chemistry Acetylsalicylic acid Phenolphthalein colorless pink

  7. Pre-lab Preparations • Weigh the tablet, then grind to a powder. • Transfer the powder to the volumetric flask, weighing to determine the amount transferred. • Add 20 mL H2O and 20 mL ethanol. • Swirl, then dilute to the mark with H2O. • It is helpful but not necessary to filter the mixture before transferring to the volumetric flask. Aspirin image: http://www.bayerhealthcare.com/html/images/upload/presse/aspirin_tablette_205.jpg Mortar and pestle image: http://www.ancientlight.info/products/images_stones/LMORL.jpg Volumetric flask image: http://www.jaytecglass.co.uk/images/VolumetricFlaskB250ml.jpg

  8. Typical Apparatus Schematic image: http://www.fao.org/docrep/v5380e/V5380E17.GIF Burette image: http://www.thesciencefair.com/Merchant2/graphics/00000001/5x8SingleSheet50mlTeflon_M.jpg Burette close-up images: http://www.pelletlab.com/v5Files/pellet/144992/640/veegee_burette.jpg

  9. Microscale Titration A SIMPLER SYSTEM Syringe image: http://www.jolly-medical.com/doc/1/syringe%20picture/syringe%201ml%20insulin.jpg Needle image: http://www.1st-product.com/uploads/10/45-1/Dispsable_Syringe_Needle_CE_ISO_273.jpg Pipette tip image: http://image.made-in-china.com/2f0j00bCkQEqMyEhoe/Pipette-Tips.jpg

  10. Procedure • Place 1.0 mL of the aspirin solution in a small Erlenmeyer flask. • Add a few drops of phenolphthalein solution as an indicator. • Using a 1.0 mL syringe, carefully titrate with 0.05 M NaOH solution, recording the initial and final volume.

  11. Data Table

  12. Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Safety glasses image from: http://facilitysigns.wordpress.com/category/signs-and-labels/

  13. Break for …. Laboratory session

  14. Calculations (Experimental data for a 20 mL sample of aspirin (ASA) solution, titrating with 0.0462 M NaOH) (11.20 mL)(0.0462 mol/L) / 20 mL = 0.0259 mol/L The amount of ASA per 20-mL sample is then: (0.0259 mol/L)(180 g/mol)(0.020 L) = 0.093 g In the 100-mL solution originally prepared: 0.093 g x 5 = 0.465 g

  15. Calculations The original tablet weighed 0.5819 g, and the amount of tablet used was 0.5716 g, so the ASA content of the original tablet is: (0.5819/0.5716) x 0.465 g = 0.473 g or (0.473 / 0.5819) * 100% = 81.4% (US regulations require each tablet to contain 500 ± 50 mg.)

  16. Other Approaches • Back-titration – add excess base, then titrate with acid. • Electrochemical methods. • Spectrophotometric – Fe(III) complex (hydrolysis in 1 M NaOH). • Total fluorescence spectroscopy - 1% acetic acid in CHCl3. • Raman spectroscopy. • High performance liquid chromatography • Larger volumes of chemicals. • Hazardous waste. • Specialized equipment. • Hazardous processing steps. Image: http://www.scielo.br/img/revistas/jbchs/v20n2/a22fig04.gif

  17. Green Relevance Green Concepts • Safer reagents. • Waste prevention. • Consider Green Principles • #1 (prevent waste) • #3 (use less hazardous substances) • #4 (safer chemicals) • #5 (safer solvents and auxiliaries) • #7 (renewable feedstocks) • #11 (real-time analysis) Botanic image: http://www.therampantgardener.co.uk/salix_alba_caerulea-cricket_bat_willow.html

  18. Connecting Solubility, Equilibrium, and Periodicity Premise • We can use chemical knowledge to make informed predictions about properties of materials too dangerous to work with. Chemical Concepts • Equilibrium; solubility; solubility product; periodic properties; acid/base titration.

  19. Background • Solubilities of metal hydroxides vary with row in the periodic table – Be < Mg < Ca < Sr < Ba. • Other experiments to illustrate periodic trends can be unsafe – e.g., reactivities of Na, K. • Beryllium compounds are particularly toxic. • Barium compounds should be used with caution (though used as medical imaging agent). • Strontium compounds are not too bad. Image: http://www.chemicalconnection.org.uk/chemistry/topics/images/lmw9d.jpg

  20. Reaction Chemistry • Titration of M(OH)2 with HCl: • M(OH)2+ 2 HCl= M2+(aq) + 2 Cl-(aq) + 2 H2O • (M = Mg, Ca, Sr)

  21. Pre-lab Preparations • Stir 2 days, then allow to stand for 1 week. • Decant into clean container just before use. • Sr(OH)2 is easy to make from SrCl2 (aq) and NaOH (aq) - just mix the solutions, filter off the product, and dry in an oven. Magnesium hydroxide image: http://sustainability.ucsb.edu/LARS/programs/chem_db/photos/663.jpg Calcium hydroxide image: http://www.aquariumlighting.com/Wholesale_Only/images/ESV_Calcium_Hydroxide.jpg

  22. Procedure • Place the desired M(OH)2 solution in an Erlenmeyer flask. • Mg(OH)2-- 5.0 mL • Ca(OH)2-- 1.0 mL (also add 50 mL H2O) • Sr(OH)2-- 0.5 mL(also add 50 mL H2O) • Add a few drops of phenolphthalein solution as an indicator. • Carefully titrate with 0.002 M HCl solution, recording the initial and final volume. • Mg(OH)2 -- use syringe (approx. 0.5 – 0.8 mL) • Ca(OH)2 -- use burette (approx. 20 – 22 mL) • Sr(OH)2 -- use burette (approx. 30 – 33 mL)

  23. Data

  24. Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Image from: http://facilitysigns.wordpress.com/category/signs-and-labels/

  25. Break for …. Laboratory session

  26. Calculations • Solubility product = Ksp = [M2+][OH-]2 • [M2+] = 0.5 [OH-] • Ksp = 0.5 [OH-]3 • [OH-] = mL HCl x 0.002 mmol-mL-1 / Vsample (mL)

  27. Results • Reported Ksp values (note variability in literature) • Mg(OH)2 -- 5.6 x 10-12 – 1.8 x 10-11 • Ca(OH)2 -- 4.7 x 10-6 – 5.5 x 10-6 • Sr(OH)2 -- 6.4 x 10-3 • Be(OH)2 -- 6.9 x 10-22 • Ba(OH)2 -- 5.0 x 10-3

  28. Other Approaches • Radiochemical determination, using Ba-137 (g, t1/2 = 153 sec). • PbCl2, AgCrO4, … • Reduced quantities. • Protective equipment. • Hope for no accidents! • Simulations. • Risk of accidental exposure. • Disposal of toxic waste. • Loss of opportunity to explore important chemical issues. Image from: http://img.brothersoft.com/screenshots/softimage/s/salts__solubility-305259-1258523535.jpeg

  29. Green Relevance Green Concepts • Waste prevention. • Avoiding hazardous chemicals • Consider Green Principles • #1 (prevent waste) • #3 (use less hazardous substances) • #11 (real time monitoring) • #12 (use substances in forms that minimize hazards)

  30. Questions and Discussion Image from: http://www.legis.state.wi.us/senate/sen11/news/images/questions.jpg

  31. Preparation for the Next Workshop (Demonstrations) • Greening the Blue Bottle Packet reports: 600+ mL container with cap 4.80 g ascorbic acid 1.00 g NaCl 150 mg NaHCO3 45 mg CuSO45H2O 3.6 mg methylene blue 600 mL H2O (We will try smaller scale – ½ - ¼ of all amounts.) Methylene blue image: http://www.petsmart.com/graphics/product_images/pPETS-3758964t400.jpg

  32. Preparation for the Next Workshop • Factors Influencing the Rate of a Chemical Reaction • One packet dry yeast • One pint of 3% hydrogen peroxide • Two clear kitchen storage bags (quart size) • Two small vials with caps • Matches and cigarette (or other object • to produce glowing embers) Cigarette image: http://www.prlog.org/10426002-cigarette-serial-killer.jpg Yeast image: http://ninecooks.typepad.com/photos/uncategorized/2008/04/08/yeast1.jpg Vial image: http://ecx.images-amazon.com/images/I/316wTFca6BL._SL500_AA280_.jpg Bag image: http://www.supplierlist.com/photo_images/66082/LDPE_Ziplock_Bag_Plastic_Bag_Packaging_Bag_Zip_loc.jpg

  33. Preparation for the Next Workshop • A Chemical Clock Reaction • Starch solution (1/2 teaspoon of starch in 100 mL of boiling water) • Vitamin C (100 mg in 6 mL of water, or 1-g effervescent pill in 60 mL of water) • 2% Tincture of iodine (1.8 – 2.2 g of I2 and 2.1 – 2.6 g of NaI in 50 mL ethanol, diluted to 100 mL with water.) • Hydrogen peroxide, H2O2 (3%) • 6 10- or 20-mL beakers • 3 20-mL Erlenmeyer flasks • 1 10-mL graduated cylinder • 4 plastic Beral pipets • 1 timer (or a watch that measures seconds) Tincture image: http://periodictable.com/Samples/053.12/s12s.JPG

  34. ขอบคุณครับ สวัสดีครับ

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