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Green Chemistry Workshop #2: Analytical Chemistry I

Green Chemistry Workshop #2: Analytical Chemistry I. US – Thai Distance Learning Program January 27, 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 #2: Analytical Chemistry I

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  1. Green Chemistry Workshop #2:Analytical Chemistry I US – Thai Distance Learning Program January 27, 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. Oxygen Content of Air Premise • Measuring the volume change of air in contact with an Fe(II) solution provides a measure of the percent O2 in air. Chemical Concepts • Acidic, basic, amphoteric oxides; direct combination reactions; preparation and properties of O2; physical nature of reactants; acid and base properties; stoichiometry; redox; gas solubility; volume.

  4. Background • Fe(II) oxidizes slowly at pH < 7 • Fe(II) oxidizes quickly at pH > 7. • This allows us to prepare solutions of Fe(II) in contact with air, then to induce the reaction with O2 when we are ready.

  5. Reaction Chemistry FeSO4 + O2 pH < 7 Fe(II) + O2 Fe(III) slow pH > 7 Fe(III) fast Fe(OH)3, Fe2O3, FeOH(SO4), Fe2(SO4)3, …?

  6. Materials two 1 mL syringes 1 cm tubing 0.4 mL of 0.2 M FeSO4 1.0 mL of 2 M NaOH Syringe image: http://www.nordiccell.com/embryo-transfer/images/HSW/HSW-1-ml.jpg Beaker image: http://www.chemistry.wustl.edu/~courses/genchem/Labs/Quant/images/150mlBeakers.gif Tubing image: http://shop1.actinicexpress.co.uk/shops/partsforaircraft/images/catalog/tygon-1.jpg

  7. Apparatus and Procedure measure final volume of air carefully!! 0.4 mL of 2 M NaOH + 0.5 mL of air 0.4 mL of 0.2 M FeSO4 1 cm flexible transparent tubing (filled with 2 M NaOH) measure initial volume of air carefully!!

  8. Calculations Check limiting reagent: 0.4 ml of 0.2 M FeSO4 = 8.0 x 10-5 moles Fe(II) 0.5 mL of air ~ 0.1 mL of O2 = 4.1 x 10-5 mole O2 PV = nRT N = PV/RT = (760 mm-Hg)(0.001 L) (62.364 L-mmHg-mol-1-K-1)(298 K) There is enough Fe(II) to consume all the O2. R = 0.0821 L-atm-mol-1K-1 = 62.364 L-mmHg-mol-1-K-1

  9. Calculations Vfinal - Vinitial = VO2 % O2 in air = (VO2/Vinitial) x 100%

  10. 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/

  11. Break for …. Laboratory session

  12. Calculations Vfinal - Vinitial = VO2 % O2 in air = (VO2/Vinitial) x 100%

  13. Other Approaches • Orsat analyzers (alkaline pyrogallic acid and/or • chromium (II) chloride solutions) • Electrochemical determinations • Quenching of room-temperature phosphorescence • Quenching of luminescence • Use of a paramagnetic oxygen analyzer • Hazardous reagents (exposure risks, waste disposal) • Specialized equipment (expensive to purchase and operate) Orsat analyzer image: http://img.tradeindia.com/fp/1/051/525.jpg Paramagnetic O2 analyzer image: http://www.fik-net.co.kr/prod/gas-de.gif

  14. Green Relevance Green Concepts • Safer chemicals and solvents – compare reagents used in other determinations of oxygen content. • Prevention of waste. • Consider Green Principles • #1 (prevent waste) • #2 (atom economy) • #3 (use less hazardous substances) • #8 (avoid derivatives) • #10 (design for degradation) • #11 (real time monitoring) • #12 (use substances in forms that minimize hazards).

  15. CaCO3 Content of Eggshells Premise • CaCO3 reacts with acids to produce CO2. • By measuring the volume of CO2 produced, we can determine how much CaCO3 was present in a sample of eggshell of known mass. Chemical Concepts • Decomposition reactions; reactivities of oxides; preparation of CO2; acid-base properties; stoichiometry; gas law.

  16. Background • Eggshells are constituted primarily of calcite – a crystalline form of CaCO3. • Shell formation is governed by LeChatelier´s principle. Carbonate ions are produced by: CO2(g) + H2O ⇄ CO2 (aq) ⇄ H2CO3 H2CO3 ⇄ H+ + HCO3- HCO3- ⇄ H+ + CO32- • Shell and membranes production occurs in a gland of the urogenital system of the female bird: CO32-(aq) + Ca2+(aq) ⇄ CaCO3(s)

  17. Reaction Chemistry • If the eggshell is treated with an acid, it will dissolve through the reverse of the process by which it is formed. CaCO3(s) + 2H+(aq)  Ca2+(aq) + H2O(l) + CO2(g) • By measuring the volume of CO2 produced, we can determine how much CaCO3 was present.

  18. Materials 0.2 g crushed egg shell Eggshell image: http://www.faqs.org/photo-dict/photofiles/list/859/1289egg_shell.jpg Scale image: http://www.popgadget.net/images/kitchen-scale-open.jpg Mortar and pestle image: http://www.ancientlight.info/products/images_stones/LMORL.jpg Plastic caps image: http://www.sks-science.com/images/240804LRG.jpg Syringe image: http://www.refillsupermarket.co.uk/images/serringue60.jpg Beaker image: http://www.chemistry.wustl.edu/~courses/genchem/Labs/Quant/images/150mlBeakers.gif 10 mL 3N HCl

  19. Apparatus and Procedure measure final volume measure volume 10 mL 3N HCl

  20. Calculations Vfinal - Vinitial = VCO2 PV = nRT n = moles of CO2 = PV/RT = moles of CaCO3 in sample If eggshell were pure CaCO3 (MW 100.09 g-mol-1): x.xx g x 1 mole/100.09 g = y.yy mole % CaCO3 = (n/y.yy) x 100% = R = 0.0821 L-atm-mol-1K-1 = 62.364 L-mmHg-mol-1-K-1

  21. 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/

  22. Break for …. Laboratory session

  23. Calculations Vfinal - Vinitial = VCO2 PV = nRT n = moles of CO2 = PV/RT = moles of CaCO3 in sample If eggshell were pure CaCO3 (MW 100.09 g-mol-1): x.xx g x 1 mole/100.09 g = y.yy mole % CaCO3 = (n/y.yy) x 100% = R = 0.0821 L-atm-mol-1K-1 = 62.364 L-mmHg-mol-1-K-1

  24. Green Relevance of the CaCO3 Experiment Green Concepts • Waste as a feedstock. • Renewable feedstocks. • Consider Green Principles • #1 (prevent waste) • #7 (renewable feedstocks) • #3 (use less hazardous substances) • #11 (real time monitoring) • #12 (use substances in forms that minimize hazards).

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

  26. สวัสดีครับ

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