Transcript Green ChemistryWorkshops

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
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
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.
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.
Reaction Chemistry
FeSO4 + O2
Fe(II) + O2
pH < 7
Fe(III)
slow
pH > 7
Fe(III)
fast
Fe(OH)3, Fe2O3, FeOH(SO4), Fe2(SO4)3, …?
Materials
two 1 mL syringes
0.4 mL of 0.2 M FeSO4
1 cm tubing
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
Apparatus and Procedure
measure final volume of air carefully!!
0.4 mL of 0.2 M FeSO4
0.4 mL of 2 M NaOH
+
0.5 mL of air
1 cm flexible transparent tubing
(filled with 2 M NaOH)
measure initial volume of air carefully!!
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
Calculations
Vfinal - Vinitial = VO2
% O2 in air = (VO2/Vinitial) x 100%
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
Vfinal - Vinitial = VO2
% O2 in air = (VO2/Vinitial) x 100%
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
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).
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.
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+ + HCO3HCO3- ⇄ H+ + CO32• Shell and membranes production occurs in a gland of
the urogenital system of the female bird:
CO32-(aq) + Ca2+(aq) ⇄ CaCO3(s)
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.
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
Apparatus and Procedure
measure final volume
measure volume
10 mL 3N HCl
Calculations
Vfinal - Vinitial = VCO2
PV
= nRT
R = 0.0821 L-atm-mol-1K-1
= 62.364 L-mmHg-mol-1-K-1
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% =
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
Vfinal - Vinitial = VCO2
PV
= nRT
R = 0.0821 L-atm-mol-1K-1
= 62.364 L-mmHg-mol-1-K-1
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% =
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).
Questions and Discussion
Image from: http://www.legis.state.wi.us/senate/sen11/news/images/questions.jpg
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