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
1.2
[Cu2+]
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
40
50
time (minutes)
0
-0.2
ln[C(t)/C(0)]
time (min) [Cu2+] ln[C(t)/C(0)]
0
1
0
3
0.8
-0.22314
9
0.65
-0.43078
23
0.5
-0.69315
28
0.4
-0.91629
45
0.2
-1.60944
0
10
20
30
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-1.6
-1.8
time (minutes)
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
• 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
O
H
C
HC
O
H
C
C
C
OH
HC
C
O- Na+
C
+ NaOH
HC
C
HC
C
H
O
C
C
H
O
C
O
+ H2O
C
CH3
Acetylsalicylic acid
O
CH3
HO
O- Na+
O
OH
+ NaOH
CO2- Na+
O
O
colorless
Phenolphthalein
pink
Pre-lab Preparations
Item
Amount
Commercial aspirin tablet
1
Ethanol
20 mL
Distilled or deionized water 80 mL
100-mL volumetric flask
1
• 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
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
1 mL syringe
(for titration)
T hree- way stopcock
1 mL syringe
(for refilling)
Automatic delivery pipet tip
TH E MEXICAN MICRO SCALE
TITRAT ION SYSTEM
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
• 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
DETERMINATION OF ASA IN COMMERCIAL ASPIRIN
Tablet mass
g ASA molar mass
180 g-mol-1
Analyzed mass
g NaOH concentration
Titration Results
Sample
mol-L-1
Calculations
Volume ASA in titration sample
g
1
mL ASA in analyzed mass
g
2
mL ASA in tablet
g
3
mL ASA in tablet
%
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/
Break for ….
LABORATORY SESSION
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
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
•
•
•
•
•
•
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 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
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: http://www.chemicalconnection.org.uk/chemistry/topics/images/lmw9d.jpg
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 Preparations
Sample Solution Sample V Titration V
Mg(OH)2 0.75 g/1.0 L 5.0 mL 0.6 – 0.8 mL
Ca(OH)2 0.50 g/0.1 L 1.00 mL 20.0 – 22.0 mL
Sr(OH)2 5.0 g/50 mL 0.50 mL 30.0 –33.0 mL
• 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
Procedure
• Place the desired M(OH)2 solution in an Erlenmeyer flask.
o Mg(OH)2 -- 5.0 mL
o Ca(OH)2 -- 1.0 mL (also add 50 mL H2O)
o 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.
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
DETERMINATION OF SOLUBILITY OF GROUP 2 HYDROXIDES
0.002 mol-L-1 HCl solution
Sample
Volume
Mg(OH)2
5.0 mL
Ca(OH)2
1.0 mL
Sr(OH)2
0.5 mL
Start
End
Used
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/
Break for ….
LABORATORY SESSION
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
• Reported Ksp values (note variability in literature)
o Mg(OH)2
-- 5.6 x 10-12 – 1.8 x 10-11
o Ca(OH)2
-- 4.7 x 10-6 – 5.5 x 10-6
o Sr(OH)2 -- 6.4 x 10-3
o Be(OH)2
-- 6.9 x 10-22
o Ba(OH)2
-- 5.0 x 10-3
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 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: http://www.legis.state.wi.us/senate/sen11/news/images/questions.jpg
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 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 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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