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 1.Prevention 2.Atom Economy 3.Less Hazardous Synthesis 4.Designing Safer Chemicals 5.Safer Solvents and Auxiliaries 6.Design for Energy Efficiency 7. Renewable Feedstocks 8. Reduce Derivatives 9. Catalysis 10. Design for Degradation 11. Real-time Analysis 12. Inherently Safer Chemistry

Cementation Experiment from Session 3

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:

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:

Reaction Chemistry Phenolphthalein Acetylsalicylic acid colorlesspink

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 H 2 O and 20 mL ethanol. Swirl, then dilute to the mark with H 2 O. It is helpful but not necessary to filter the mixture before transferring to the volumetric flask. Aspirin image: Mortar and pestle image: Volumetric flask image: ItemAmount Commercial aspirin tablet1 Ethanol20 mL Distilled or deionized water80 mL 100-mL volumetric flask1

Typical Apparatus Schematic image: Burette image: Burette close-up images:

Microscale Titration Syringe image: Needle image: Pipette tip image: A SIMPLER SYSTEM

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.

Data Table

Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Safety glasses image from:

LABORATORY SESSION Break for ….

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

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

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 CHCl 3. Raman spectroscopy. High performance liquid chromatography Image:  Larger volumes of chemicals.  Hazardous waste.  Specialized equipment.  Hazardous processing steps.

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:

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.

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:

Reaction Chemistry Titration of M(OH) 2 with HCl: M(OH) HCl = M 2+ (aq) + 2 Cl - (aq) + 2 H 2 O (M = Mg, Ca, Sr)

Pre-lab Preparations Magnesium hydroxide image: Calcium hydroxide image: 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 SrCl 2 (aq) and NaOH (aq) - just mix the solutions, filter off the product, and dry in an oven. SampleSolutionSample VTitration V Mg(OH) g/1.0 L5.0 mL0.6 – 0.8 mL Ca(OH) g/0.1 L1.00 mL20.0 – 22.0 mL Sr(OH) g/50 mL0.50 mL30.0 –33.0 mL

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

Data

Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Image from:

LABORATORY SESSION Break for ….

Calculations Solubility product = K sp = [M 2+ ][OH - ] 2 [M 2+ ] = 0.5 [OH - ] K sp = 0.5 [OH - ] 3 [OH - ] = mL HCl x mmol-mL -1 / V sample (mL)

Results Reported K sp values (note variability in literature) o Mg(OH) x – 1.8 x o Ca(OH) x – 5.5 x o Sr(OH) x o Be(OH) x o Ba(OH) x 10 -3

Other Approaches Radiochemical determination, using Ba-137 ( , t 1/2 = 153 sec). PbCl 2, AgCrO 4, … 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:

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)

Questions and Discussion Image from:

Preparation for the Next Workshop Greening the Blue Bottle Methylene blue image: Packet reports: 600+ mL container with cap 4.80 g ascorbic acid1.00 g NaCl 150 mg NaHCO 3 45 mg CuSO 4  5H 2 O 3.6 mg methylene blue600 mL H 2 O (We will try smaller scale – ½ - ¼ of all amounts.) (Demonstrations)

Preparation for the Next Workshop Factors Influencing the Rate of a Chemical Reaction Cigarette image: Yeast image: Vial image: Bag image: 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)

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 I 2 and 2.1 – 2.6 g of NaI in 50 mL ethanol, diluted to 100 mL with water.) Hydrogen peroxide, H 2 O 2 (3%) 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:

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