University of Oregon – Thailand Distance Learning Program – Green Chemistry
2010
The Percent of Oxygen 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.
Green Concepts
Safer chemicals and solvents; waste prevention. (Consider Green Principles 1, 2, 3, 8, and
10.)
Introduction
Dioxygen concentration in air is commonly measured by reacting this gas to form either a
solid or a dissolved compound. The concomitant volume change is measured, and by gas law
calculations it is translated into a volume percent of the original sample. Commercial
equipment (e.g., Orsat analyzers, which use alkaline pyrogallic acid and/or chromium (II)
chloride solutions), and laboratory demonstrations (e.g., with iron wool that yields solid iron
oxide) are based on this principle. Other methods of dioxygen analysis include
electrochemical (amperometric, galvanostatic) determinations, the quenching of roomtemperature phosphorescence, the use of a paramagnetic oxygen analyzer, and the quenching
of luminescence. Many of these procedures rely on hazardous reagents, presenting risks of
exposure and leading to waste disposal issues. Others depend on specialized equipment that
may not be readily available and that can be expensive to purchase and operate (including the
costs of electrical power).
In this experiment we present a novel, reproducible, fast, safe, green, and low cost method
based on the oxidation of dissolved Fe(II) in an alkaline medium. Appropriate for high school
and general chemistry students, it is based on the fact that the reaction between Fe(II) and O2
to produce Fe(III) is kinetically hindered at low pH, whereas at high pH it occurs in the sub
second time frame.
Laboratory
SAFETY PRECAUTIONS: Use care to avoid contact with sodium hydroxide
solutions. Use gloves and goggles.
The instructor may decide to have this experiment repeated several times so as to have
sufficient data for statistical analysis.
Materials needed
1-mL syringe (2)
1-cm of connecting hose
0.2 M FeSO4 (0.4 mL)
2 M NaOH (0.4 mL)
Copyright Kenneth M. Doxsee, University of Oregon
Page 13 of 84
University of Oregon – Thailand Distance Learning Program – Green Chemistry
2010
1. Remove the needles from two 1-mL insulin syringes and discard them properly.
Caution: these needles are extremely sharp.
2. Draw 0.4 mL of a 0.2 M FeSO4 solution into the first syringe.
3. Now draw exactly 0.5 mL of air into the second syringe and then 0.4 mL of a 2 M
NaOH solution.
4. Connect both syringes through a 1-cm long piece of a transparent and flexible rubber
tube filled with 2 M NaOH. Avoid any additional volume of air from coming into
either one of the syringe barrels. (See Figure.)
Figure. Syringe set up.
5. In a synchronized fashion, push one of the syringe‟s plungers and pull the other so as
to mix well the contents of both. Repeat this movement several times.
6. Record the amount of gas remaining at the end of this procedure. Note: For greater
precision, you may use a loupe or a similar magnifying device to read the final volume
of gas from the syringe volume marks.
7. Since the resulting solution contains Fe(III) and unused NaOH, it can be neutralized –
for example with HCl – and disposed of according to local regulations.
Questions
1. What is the number of moles of Fe and of O2 involved? Which is the limiting reagent?
2. Write a formula to calculate the % volume decrease.
3. Is the volume ratio equal to the mole ratio in a gas mixture?
Research Questions
1. Find in the literature the rate of the reaction between Fe(II) and O2 at acidic and basic
pH (e.g., at pH = 1 and pH = 10).
2. At what pH does Fe(III) precipitate?
3. What is the basis for the amperometric determination of dioxygen (the Clark method)?
References
EPA-Emissions Measurement Center. Method 3: Gas Analysis for the Determination of Dry
Molecular Weight, http://www.epa.gov/ttnemc01/promgate/m-03.pdf (Accessed 8 August
2008); K. L. Phillips, Determination of oxygen and carbon dioxide using a paramagnetic
oxygen analyzer, Biotechnology and Bioengineering 2004, 5(1), 9 – 15; ThomasNet Industrial
Newsroom® (TIN). Portable Analyzer measures oxygen in air and water,
http://news.thomasnet.com/fullstory/6734; Bacon, John R.; Demas, James N., Apparatus for
oxygen determination, United States Patent 5030420, 07/09/1991.
Copyright Kenneth M. Doxsee, University of Oregon
Page 14 of 84
University of Oregon – Thailand Distance Learning Program – Green Chemistry
2010
Determination of the Weight Percent of CaCO3 in Egg Shells
Chemical Concepts
Decomposition reactions; reactivities of oxides; preparation of CO2; acid-base properties;
stoichiometry; gas law.
Green Concepts
Waste as a feedstock; renewable feedstocks; safer solvents. (Consider Green principles 1, 4, 8,
11, and 12.)
Introduction
Egg shells are constituted primarily of calcite – a crystalline form of CaCO3. Shell formation
occurs through a series of reactions that proceed in two stages and are governed by
LeChatelier´s principle (Down & Mackay 1983). The first stage, involving respiratory
processes, occurs in blood and produces carbonate ions, according to equations 1-3.
CO2(g) + H2O ⇄ CO2(aq) ⇄ H2CO3
(1)
H2CO3 ⇄ H + HCO3
(2)
+
-
HCO3- ⇄ H+ + CO32-
(3)
The second stage – actual formation of the shell and of its membranes – occurs in a gland of
the urogenital system of the hen (Storer and Usinger). In this stage, sparingly soluble calcium
carbonate is precipitated according to equation 4.
CO32-(aq) + Ca2+(aq) ⇄ CaCO3(s)
(4)
If the egg shell is treated with an acidic solution, it will dissolve as the above process is
reversed. A balanced equation for this reverse process is provided in equation 5.
CaCO3(s) + 2H+(aq)
Ca2+(aq) + H2O(l) + CO2(g)
(5)
Given the simple 1:1 stoichiometry (with one mole of CO2(g) produced for each mole of
CaCO3(s) consumed), measurement of the volume of CO2(g) produced allows for the
calculation of the amount of CaCO3(s) present in the egg shell.
The volume of CO2 produced is measured very simply by using a 60-mL syringe as the
reaction vessel in an acid/carbonate reaction. The resulting volume of gas is converted into
grams and the percent weight is calculated. This is a simple, fast, and quantitative experiment
and typically yields results in reasonable agreement with literature values (80 – 90 weight
percent).
Copyright Kenneth M. Doxsee, University of Oregon
Page 15 of 84
University of Oregon – Thailand Distance Learning Program – Green Chemistry
2010
The experiment uses egg shells, a biologically-produced substance that representing a
potential waste product, and thus illustrates several green principles – use of renewable
feedstocks and prevention of waste – in this case, through recognition that a “waste” from
another process can in fact serve as a useful starting material. It does require the use of 3 M
HCl, however. While not a particularly hazardous concentration, and easily neutralized and
disposed of, it does lead to the generation of chloride-containing waste. In the research
questions, students are offered the opportunity to consider development of a still greener
alternative for this experiment.
Laboratory
Materials needed
Balance (accuracy 0.01 g)
60-mL syringe
Plastic cap (to fit in syringe)
150-mL beaker
A dry egg shell (from a chicken)
3 M HCl (10 mL)
Silicone oil (1-2 drops)
1. Remove the piston (from the 60-mL syringe) and lubricate its tip with a drop or two of
silicon oil; reinsert it and move back and forth a couple of times. Remove it again for
next step.
2. Grind an egg shell. Weigh out approximately 0.20 g (record the mass used!) and place
it in a plastic cap that fits in the barrel of the 60-mL syringe. Fill the syringe with
water (use one of your fingers to prevent the water from leaking out), and place the
plastic cap on top of the water (as to make it float on it). Remove your finger so that
the water comes out and the plastic cap gently moves down to the bottom of the
syringe. Then, reinsert the plunger.
3. Draw 10.0 mL of 3 M HCl into the syringe so as to make the plastic cap float on the
HCl solution. Cap the syringe tightly (for example, with a Luer Lock). Shake the
syringe and its contents vigorously so as to provoke a complete reaction between the
shell and the acid.
4. The piston moves under the pressure of the newly produced gas (CO2). When this
stops, record the new volume reached and subtract the initial HCl volume.
5. Convert this volume to standard temperature and pressure and calculate the number of
moles of CO2 produced. Calculate the grams of CaCO3 that this corresponds to, and
from here, the weight percentage in the egg shell.
Data
Mass of the egg shell used = g
Initial position of the piston = mL
Final position of the piston =
Volume of CO2 generated = mL
Ambient temperature = oC
Atmospheric pressure = atm
Volume of CO2 (converted to STP) = mL
Copyright Kenneth M. Doxsee, University of Oregon
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University of Oregon – Thailand Distance Learning Program – Green Chemistry
2010
Questions
1. What is the reported value for the percent of calcium carbonate in egg shells?
2. How does your experimental value compare?
3. If your experimental value is different from the value reported, suggest some reasons
that might be responsible for the difference.
Research Questions
1.
2.
3.
4.
5.
What is the remainder of a chicken egg shell composed of?
Do different species of birds produce eggs with different compositions?
Reptiles also lay eggs. What is known about their composition?
Some mammals also lay eggs. What are they composed of?
What reasons might there be for different types of animals to produce different types
of eggs?
6. How many chicken eggs are produced each year? Approximately how many pounds of
egg shells does this correspond to? What is done with these egg shells? Can you think
of new uses for egg shells that could lead to their being viewed as having value rather
than as trash?
7. Can you devise a modified procedure for this experiment that does not require the use
of HCl? Does your alternative represent a safer approach? What about the
environmental impacts?
References
This procedure was adapted by Jorge Ibañez (Universidad Iberoamericana, Mexico) from
Daniel Bartet P., Anamaría Jadue J., Departamento de Química, Universidad Metropolitana
de Ciencias de la Educación. Santiago, Chile (e-mail: [email protected]). References cited in
the experiment are listed below.
Brown, D.B.; Mackay J.A., “Le Chatelier‟s Principle, Coupled Equilibrium, and Egg Shells,”
J. Chem. Ed. 1983, 60, 198.
Mattson, B. “Microscale Gas Chemistry,” 2nd Edition: Educational Innovations, Norwalk,
Connecticut, U.S.A., 2001.
Storer, T. I.; Usinger R. L. “Zoología General,” Ed. Omega, Barcelona, 1960.
Copyright Kenneth M. Doxsee, University of Oregon
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