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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

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
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
determination of acetylsalicylic acid in an aspirin tablet
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

background
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

reaction chemistry
Reaction Chemistry

Acetylsalicylic acid

Phenolphthalein

colorless

pink

pre lab preparations
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

typical apparatus
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

microscale titration
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

procedure
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.
laboratory safety
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/

calculations
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

calculations1
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.)

other approaches
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

green relevance
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

connecting solubility equilibrium and periodicity
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.
background1
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

reaction chemistry1
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)
pre lab preparations1
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

procedure1
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)
laboratory safety1
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/

calculations2
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)
results
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
other approaches1
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

green relevance1
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
Questions and Discussion

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

preparation for the next workshop
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

preparation for the next workshop1
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

preparation for the next workshop2
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

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