Green Chemistry Workshop #5:
Kinetics (Demonstrations)
US – Thai Distance Learning Program
March 3, 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
Greening the Blue Bottle
Premise
• Ascorbic acid is an effective reducing
agent for methylene blue.
• Air (oxygen) can oxidize reduced
methylene blue.
• With visible color changes, these
reactions can be used to illustrate kinetics
and mechanisms qualitatively.
Chemical Concepts
• Reaction rates; mechanism of reaction.
Image: http://z.about.com/d/chemistry/1/0/S/b/bluebeaker.jpg
Background
• This is a well-known and popular demonstration used
to introduce the topic of chemical kinetics.
• Because it is popular, attempts have been made to
make it better, safer, and less waste-producing.
Reaction Chemistry
H
N
CH2OH
O
O
OH
(H3C)2N
blue
S
+
N(CH3)2
HO
methylene blue
Methylene
Blue
OH
ascorbicacid
acid
Ascorbic
H
H
N
CH2OH
O
O
OH
(H3C)2N
S
N(CH3)2
O
colorless
leucomethylene blue
Leucomethylene Blue
O
dehydroascorbic acid
Dehydroascorbic acid
Reaction Chemistry
• Ascorbic acid reduces MB+ to MBH.
• Air does not rapidly oxidize MBH back to MB+.
• Cu catalyzes the oxidation of MBH to MB+ by O2.
• (Cu also catalyzes the reduction of the MB+ by ascorbic acid.
Thus, two reduction pathways of MB+ – uncatalyzed and Cucatalyzed – are operating.)
Procedure
1
2
3
4
5
6
Item
Ascorbic acid
NaHCO3
NaCl
Methylene blue
Distilled or deionized water
CuSO4•5H2O
Amount
4.80 g
0.15 g
1.00 g
3.6 mg
600 mL
45 mg
• Weigh solid reagents 1 – 4, place in container that
can be tightly capped.
• Methylene blue can be added as 1-2 drops of
commercial MB solution.
• Add water, cap, and swirl/shake until dissolved.
• Add the CuSO4•5H2O
Methylene blue image: http://www.petsmart.com/graphics/product_images/pPETS-3758964t400.jpg
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
Results
• Qualitatively, observe redox chemistry as it occurs through
color change.
• The blue bottle has been used for experimental measurement of
kinetics – using spectrophotometric observation of the loss of
MB+ color (S. Mowrey & P. J. Ogren, Journal of Chemical
Education 1999, 76, 970-973).
• We could perhaps do this visually, as we did with the
cementation reaction.
• We will instead explore the kinetics of a different reaction of
ascorbic acid – the clock reaction.
Other Approaches
• Glucose as the reductant.
• Other kinetics experiments.
o Various chemical reactions.
o Computer simulations.
 Large quantities of reagents (typical 20 g glucose, 16 g KOH)
 Hazardous waste.
 Strongly basic solution.
 Poor quality – glucose degrades to yellow byproducts.
Simulation image from: http://www.chm.davidson.edu/vce/Kinetics/RateOfReaction.html/
Green Relevance
Green Concepts
• Safer reagents.
• Waste prevention.
• Consider Green Principles
– #1 (prevent waste)
– #4 (safer chemicals)
– #11 (real-time analysis)
Cat image: http://www.cbruen.com/blog/cat_green_glasses_82006.jpg
Bottle image: http://www.couronneco.com/upload/images/product/large/0555W58_small_blue_bottle_re.jpg
A Chemical Clock Reaction
Premise
• A reaction system that gives a dramatic color change
when the reaction is complete can be used to allow a
simple exploration of the factors influencing the rate
of a chemical reaction.
Chemical Concepts
• Reaction kinetics; effect of concentration on kinetics;
redox chemistry; halogens; vitamin C.
Background
• Clock reactions – reactions in which a readily
observable change occurs at a reproducible period of
time after the initial mixing of reactants – date back
to at least 1886, when Landolt reported the “iodine
clock reaction” (H. Landolt, Ber. Dtsch. Chem. Ges.
1886, 19, 1317-1365.)
Image: http://www.chemicalconnection.org.uk/chemistry/topics/images/lmw9d.jpg
Reaction Chemistry
• Ascorbic acid (AA) reduces elemental iodine to the colorless
iodide ion:
AA + I2 → 2I- + oxidized AA + 2H+
• Hydrogen peroxide (H2O2) oxidizes iodide back to iodine:
2H+ + 2I- + H2O2 → I2 + 2H2O
• As long as AA is present, iodine is reduced back to iodide. When
all the AA has been oxidized, elemental iodine accumulates. In
the presence of starch, this produces an intense blue color:
I2 + starch → blue I2/Starch complex
Pre-lab Preparations
• Starch solution (boil 1/2 teaspoon of starch in 100 mL of
water, then cool to room temperature)
• Ascorbic acid (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%)
Tincture image: http://periodictable.com/Samples/053.12/s12s.JPG
Procedure
Solution 1
Solution 2
Water Vitamin C Iodine Water H2O2 Starch
Final Volume
(mL)
Test 1 3 mL
1 mL
1 mL
3 mL 1 mL 1 mL
10
Test 2 3 mL
1 mL
1 mL
2 mL 2 mL 1 mL
10
Test 3 3 mL
1 mL
1 mL
1 mL 3 mL 1 mL
10
• Prepare the three Test solutions of Solution 1.
• Prepare the three Test solutions of Solution 2.
• For each Test, pour Solution 2 into Solution 1, swirl briefly,
record the starting time, and allow the mixture to stand.
• Record the time when the solution changes color.
Data
% Hydrogen peroxide Time (seconds)
Test 1
Test 2
Test 3
Laboratory Safety
Accident: An unexpected and undesirable event,
especially one resulting in damage or harm.
• Starch solution
• Ascorbic acid (Vitamin C)
• 2% Tincture of iodine
• Hydrogen peroxide, H2O2 (3%)
Image from: http://facilitysigns.wordpress.com/category/signs-and-labels/
Break for ….
LABORATORY SESSION
Calculations
Test 1:
1 mL 3% H2O2 ends up in 10 mL of solution
… so 0.3% H2O2
% Hydrogen peroxide Time (seconds)
Test 1
0.3 %
Test 2
0.6 %
Test 3
0.9 %
Other Approaches
• Typical iodine clock reactions call for the use of sulfuric acid,
perchloric acid, or ammonium persulfate.
• Other clock reactions are known.
– E.g., the “Old Nassau” reaction (HgI2 precipitation;
iodide/iodate; metabisulfite/hydrogen sulfite)
– Bromate/bromide; phenol; sulfuric acid
 Hazardous reagents.
 Disposal of hazardous waste.
Image from: http://www.notjustscience.co.uk/content/images/dutch_football.jpg
Green Relevance
Green Concepts
•
•
•
•
Waste prevention.
Safer chemicals and reactions.
Renewable feedstocks.
Consider Green Principles
– #1 (prevent waste)
– #4 (safer chemicals)
– #5 (safer solvents)
– #7 (renewable feedstocks)
– #11 (real time monitoring)
Image from: http://freshome.com/wp-content/uploads/2008/05/colours_clock.jpg
Factors Influencing the Rate of a Chemical
Reaction
Premise
• Simple experiments using household
materials can be used to explore various
issues about chemical kinetics.
Chemical Concepts
• Reaction rate; catalysis.
Background
• Baker’s yeast contains an enzyme – catalase – that
decomposes H2O2 to O2 and H2O.
• Most organisms contain catalase (or catalase type)
enzymes, to destroy H2O2.
• Catalase solutions are used in contact lens cleaning,
to remove residual H2O2 cleaning solution.
Imagehttp://www.aclens.com/accessoryphotos/42_lg.jpg
Reaction Chemistry
2 H2O2 → 2 H2O + O2
Heme image: http://redandr.ca/vm3/Heme.jpg
Catalase image: http://en.wikipedia.org/wiki/File:Catalase_Structure.png
Procedure
• Fill one bag with air and seal.
• Place small capped vial of yeast (1/4 packet) and 50-75 mL of
3% H2O2 in a second bag. Trapping as little air as possible,
seal the bag.
• Cautiously touch burning cigarette to each bag, observe.
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
Laboratory Safety
Accident: An unexpected and undesirable event,
especially one resulting in damage or harm.
• Sparks/flame
• Hydrogen peroxide, H2O2 (3%)
Safety glasses image from: http://facilitysigns.wordpress.com/category/signs-and-labels/
Break for ….
LABORATORY SESSION
Other Possibilities
• This procedure demonstrates the effect of O2
concentration on the rate of combustion of plastic.
• Other things that can be explored include:
– Effect of temperature – cool the mixture in ice before
mixing yeast with H2O2, observe rate at which O2 is
produced.
– Effect of surface area – grind the yeast to a fine
powder, observe rate at which O2 is produced.
– Other ideas that you or your students may have.
Green Relevance
Green Concepts
•
•
•
•
Catalysis.
Safer chemicals and reactions.
Renewable feedstocks.
Consider Green Principles
– #1 (prevent waste)
– #4 (safer chemicals)
– #5 (safer solvents)
– #7 (renewable feedstocks)
– #9 (catalysis)
Questions and Discussion
Image from: http://www.legis.state.wi.us/senate/sen11/news/images/questions.jpg
Preparation for the Next Workshop
• Polymer Packing “Peanuts”
Polystyrene “peanuts
Biodegradable “peanuts”
Acetone (10 – 25 mL)
Water (10 – 15 mL)
Containers – beakers or jars
Image: http://www.turtlerescues.com/images/packing%20peanuts%20on%20top%20of%20inside%20box.jpg
Preparation for the Next Workshop
• Carbohydrates
hot plate
pectin
fruit juice
(apple or white grape)
table sugar
(sucrose)
Pectin image: http://www.pickyourown.org/blueberry/pectin_types.jpg
Apple juice image: http://hotelminishop.com/Dole_apple.jpg
Hot plate image: http://www.vanpetro.com/LabEquipment/UsedLab_HotPlate.JPG
Sugar image: http://img.alibaba.com/photo/100383368/Sugar_Thailand_Origin.jpg
Preparation for the Next Workshop
• Analysis of Charge with Polymer Gels
disposable baby diaper
small plastic cups
(communion cups)
Colored inorganic salts – CuSO4•5H2O, KMnO4
Samples of cationic and anionic dyes - examples:
methylene blue
malachite green
crystal violet
food coloring agents - red, blue, green
Plastic cups image: https://www.inspire4less.com/productimages/9780784725290.jpg
Disposable diaper image: http://reflectionsofamirror.files.wordpress.com/2008/02/disposable_baby_diaper.jpg
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