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Reflection 4:  Application of Scientific Concepts

How the rubric item was addressed in this reflection:
This reflection shows how I have grown in the ability to apply concepts and scientific principles to practical problems and/ or real-world situations, rather than just to my teaching.

WHAT is the evidence? WHY did I choose the evidence? HOW does the evidence show growth?

As a result of the MCE content courses (and in large part, the small anecdotes and side stories professors tell), I have an improved ability to apply scientific concepts to real-world situations.  I present 3 sets of evidence (baseline and later) that show how I have grown in thinking about and understanding the chemistry behind real-world phenomena such as


EVIDENCE #1
Saponification, fatty acids, micelle formation and soap
Baseline Evidence:
  1. Organic Chem II (C3444, Spring 2001) textbook* excerpts
  2. REFLECTION
 Later Evidence:

Chem503
  1. Saponification/ household soap problem (#9), in Problems for November 17th class
    OCTOBER 2007
  2. Detergent problem (#3), in Workshop Problems for February 23rd class
    FEBRUARY 2008
  3. Ester/ fat (III) & detergent question (IV), in QUIZ #6, February 23rd
    FEBRUARY 2008
My first exposure to Fischer esterification, saponification, and the application of saponification to making soap occurred in my junior year Organic Chemistry course.  There are several reasons why I did not connect these concepts to each other and to any real-life application:
  • the focus of the Organic course was primarily mechanistic and somewhat disjointed in its connection to real-life applications.  This can be seen by the stress on mechanisms and classification of reactions by functional group (rather than on biology or consumer applications) in the textbook (See Chapter headings and page numbers of textbook excerpts).  The topic of "soap formation" was presented well after the chapters on esterification and saponification reactions.
Excerpts from Undergraduate Organic Chemistry textbook*:
(click on thumbnail image to see larger view)

Fischer esterification & saponification
orgo 1
 orgo2
 orgo3
21.3 Nucleophilic Acyl Substitution Reactions of Carboxylic Acids
 21.6 Chemistry of Esters
p. 856
 p. 867-8 (11 pages later)

Soap and micelle formation
orgo4
 orgo5
27.2 Soap
p.1122-3 (more than 250 pages later)

  • I did not have a sufficiently intuitive understanding of the structure of a fat (i.e. the three ester bonds that connect the fatty acids to the glycerol) that would allow me to classify it as an ester that would undergo saponification reactions in college.  I gained this understanding when I had to teach one section of biology in 2004-2005 (which started with a molecular biology unit).
*McMurry, J. (2000). Organic Chemistry (5th ed.), NY: Brooks/ Cole (Thompson Learning).
Chem503
Saponification/ household soap problem
Question #9
Problems for November 17th class
(click on image for larger view)
9

Chem503
Detergent problem
Question #3
Workshop Problems for February 23rd class
(click on image for larger view)
3

Chem503
Ester/ fat problem
Question III
Quiz #6, February 23rd
(click on image for larger view)
iii

Chem503
Ester/ fat problem
Question III
Quiz #6, February 23rd
(click on image for larger view)
iv
REFLECTION & SUMMARY OF CONTENT:
I grew in my ability to apply my understanding of esterification and saponification to the production and use of soaps through homework sets, quizzes, POGILs (especially the Fischer esterification POGIL), and Dr. Robert's personal anecdotes in Chem503.  Growth is shown by my ability to identify the properties of a molecule's structure that make it useful as a detergent, as well as how fats can be saponified to produce fatty acid salts that have detergent action.  There are several major enduring understandings that I have gained (though not in any linear, easy to follow fashion) that have made my understanding of detergents more comprehensive and accurate.

  • Detergents are substances that are amphipathic (have both polar and nonpolar portions), where the polar end interacts with water and the nonpolar end interacts with grease, forming micelles.
    (Overview, Feb 23, 2008: "A soap molecule includes a highly polar carboxylate salt at one end, the hydrophilic end, and a highly nonpolar hydrocarbon chain extending to the other end, the hydrophobic end.  When soap is dissolved in water, th emolecules cluster together to form a micelle, a spherical organization in which the nonpolar hydrocarbon chains are turned inward so as to interact with each other through London attractions and the polar carboxylate salt ends are turned outward so as to interact with water molecules through hydrogen bonding.  It's a kind of "circle the wagons" effect.  Soaps clean by dissolving grime and grease, which is nonpolar, in the interior of the micelle and thus separating it from whatever is being cleaned."

  • Carboxylic acids with long hydrocarbon tails (i.e. fatty acids) have the ideal properties for a detergent.
    (E.U. Feb 23, 2008: III.b.  Soaps are produced by the saponification of triglycerides and effect their cleansing action by forming micelles which encapsulate grease.)

  • Fats are esters.
    (Overview, Feb 23, 2008: "Fats and oils are triglycerides, which are esters of fatty acids with glycerol.")

  • Hydrolysis of fats (a saponification reaction) produces carboxylic acids and alcohols; saponification can be thought of as the "reverse" reaction of Fischer esterification.
    (Overview, Feb 23, 2008: "The base-promoted hydrolysis of an ester is called saponificiation.  Saponificiation of fats and oils leads to glycerol and a mixture of salts of fatty acids, which is soap.)
SUMMARY OF CONTENT

In saponification, bases (OH-) react with esters (RCOOR') to produce carboxylic acids (RCOOH) (which form carboxylate ions (RCOO-) when deprotonated) and alcohols (R'OH).   This is the opposite of Fischer esterification, in which alcohols and carboxylic acids, in the presence of acid catalyst, react to form esters.

Soap from fat:
An understanding of this reaction can be used to explain the making of soap from fat.  Fat contains three ester bonds that combine 3 fatty acids to a glycerol (triol).  Saponification hydrolyzes the ester bond (i.e. the hydroxide attacks the carbonyl carbon in a nucleophilic substitution reaction which kicks off the -OR group of the ester, which later protonates to form the alcohol, ROH), forming fatty acids that contain long hydrophobic alkyl chains and charged deprotonated carboxyl groups.  These fatty acids can trap hydrophobic particles in spherical micelles, helping wash grease away.  The polar heads are attracted to water while the nonpolar chains of the fatty acids are attracted to grease.

Other detergents:
Any substance that is amphipathic can form these detergent micelles.  The polar parts are hydrophilic, and the nonpolar parts are hydrophobic/ lipophilic and will adhere to grease.  Some of these detergents avoid the precipitation of fatty acids in acidic water and insoluble fatty acid salts in hard water.


EVIDENCE #2
Using an understanding of oxidation-reduction potential (ORP) to solve the mystery of
how people were getting lead poisoning from the drinking water in Washington, D.C.
Baseline Evidence:
  1. General Chem II (C1404, Spring 2000) self-made review sheet on electrochemistry and electrochemical cells
  2. General Chem II (C1404, Spring 2000) notes on how acidity and Ksp dictate Pb solub
  3. REFLECTION
 Later Evidence:

Chem505
PIM #3: Lead in the drinking water of Washington, D.C.
AUGUST 2008
As part of my undergraduate major requirements (Environmental Chemistry), I completed the coursework for a Chemistry degree (minus a thesis project) and took introductory courses about the biosphere, climate, the earth system, and environmental field methods.  While I had learned about oxidation potentials and the effect of acidity on lead solubility in my General Chemistry course, I had not encountered much discussion of electrochemistry or pH in my environmental courses.  I certainly do not remember ever seeing an oxidation reduction potential-pH diagram detailing the solubilities and form of a particular metal in a range of conditions. 

My studies had not focused on the application of environmental chemistry to specific urban problems--like lead free drinking water, but rather on more broad, global phenomena (e.g. albedo of different parts of the earth, plate tectonics, deep ocean currents, Hadley cell transport, biomass calculations).

GChem electrochemistry review sheet:
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electrochem notes


GChem notes on Ksp, acidity, and lead solubility:
(click on image for larger view)
lead notes
The PIM #3 writeup:
(click on image for .pdf file)
pim 3


The ORP (oxidation reduction potential) diagram that explains how chloramine use changed the solubility of lead:
(click on image for larger view)
orp diagram

References:
  1. Schock, M. R., J. Swertfeger, S. M. Harmon, R. Lohmann, AND J. DeMarco. (2001). Tetravalent lead: A hitherto unrecognized control of tap water lead contamination.  Presented at AWWA Water Quality Technology Conference, Nashville, TN 11/11-14/2001.
  2. Renner, R. (2004). Plumbing the depths of D.C.'s drinking water crisis. Environmental Science & Technology, 38(12), 224A-226A.
  3. Edwards, M. & Dudu, A. (2004). Role of chlorine and chloramine in corrosion of lead-bearing plumbing materials. Journal of the American Water Works Association, 96(10), 69-81.
REFLECTION:
I gained my understanding of the connection between pH, the oxidation-reduction potential of water, and the solubility/ oxidation states of heavy metals (e.g. Pb) in Chem505 in the course of lectures and PIM #3.  Growth is shown by my ability to interpret the Eh-pH diagram for a Pb-H2O-CO3 water system.  I grew in my ability to determine the type of lead species in a water sample and to assess the benefits and dangers of varying pH and oxidation conditions in drinking water.

SUMMARY OF CONTENT:
(from Review Questions For Final):
  • Michael Schock has insisted for decades that maintaining pH of drinking water between ~6.4 and ~10.2 would help minimize pipe corrosion.  What is significant about these values of pH?

    -Water's natural Eh (ORP or oxidation reduction potential) values correspond to the diagonal dashed lines in the ORP diagram to the right.  At pH's between these ranges, shown by the vertical dotted lines, some of the soluble Pb+2 is precipitated as insoluble PbCO3 and Pb 3(CO3)2(OH)2 in the presence of CO32- ions.
  • Why was solubility of Pb in water never a problem before the Washington, DC drinking water utility decided to change its disinfection chemistry?

    -Before Washington, DC changed its disinfection chemistry, Pb in water wasn't a problem because Cl2 was used to disinfect water.  The byproducts of     Cl2 disinfection are HOCl and OCl-, which are highly oxidizing and therefore Pb in this environment is found as insoluble tetravalent lead PbO2--which exist as very hard, reddish brown scales (see green dot on diagram).
  • Why did the Washington, DC drinking water utility change its disinfection chemistry? If the Washington, DC drinking water utility (or any other) used groundwater instead of water from the Potomac River, could they still use Cl2 for all of their treatment and still meet the standards of the Disinfection Byproduct Rule from EPA?  Briefly explain.

    -Because DC gets its water from the Potomac River, there are high concentrations of humic acid from the decomposition of organic matter.  These humic acids react with HOCl to form trihaloalkanes (THA) (e.g. chloroform, CHCl3), which are carcinogenic.  In 2001, the Washington Aqueduct changed disinfection methods to comply with new "disinfectoin byproducts" rule whiich requires cutting the concentratio of chloroform to <0.08 ppb.  However, by tring to reduce the production of THAs by disinfecting water with chloroamine (NH2Cl), the ORP value was lowered, increasing the solubility of lead by reducing the fairly insoluble Pb+4 to the more soluble Pb+2.  With chloramine treatment, brass fixtures galvanically corrode, releasing lead contaminants as the copper in pipes acts as a cathode.  One solution of decreasing solubility of lead by increasing pH (by adding PO43-) may actually accelerate galvanic corrosion.  The use of ozone, O3, to destroy humic acid, may be another solution.


EVIDENCE #3
Using an understanding of quantum theory to explain how fluorescent light bulbs work
and why they are more energetically efficient than incandescent light bulbs
Baseline Evidence:
  1. General Chem I (C1403, Fall 1999) (preliminary) textbook excerpt (Leonard Fine, one of the authors, was my professor)
  2. Notes from Chem506 on different types of light bulbs
    AUGUST 12, 2008
 Later Evidence:

Chem507
Lightbulb emission spectra activity
SEPTEMBER 2008
Unfortunately, while I do not still have my GChem notes from sophomore year of college, I do know that I first learned about how an incandescent light bulb worked in that course.  The tungsten combustion responsible for the glow was tied into the unit on combustion and stoichiometry.

There was no mention of halogen or CFL bulbs.  The following is an excerpt from my GChem book (co-written by my professor, Leonard Fine).
GChem textbook* excerpt on incandescent lightbulbs:
(click on image for larger view)
G-Chem text

*Fine, L.W., Beall, H., & Steuhr, J. (2000). Seeing things: The incandescent lightbulb and the tungsten filament. In Ch 3: Stoichiometry In Chemistry for Scientists and Engineers (Preliminary ed.). New York: Harcourt College Publishing, p. 101.
I first encountered a meaningful explanation for the way that CFLs and fluorescent light bulbs worked in Chem506 (I wrote the notes down because it was new and interesting for me).  It surprised me that fluorescent lights and blacklights had the same structure, except for the phosphor coating on the inside of the lightbulb.  This second piece of evidence documents the beginning of my understanding of how CFLs worked.

Chem506 notes re: light bulbs:
(click on image for larger view)
notes
The lightbulb activity writeup:
(click on image for .pdf file)
summary about lightbulbs

A schematic of a CFL bulb:
cfl bulb

An example of how different phosphor coatings produce different color lights (all versions of white):
lightbulbs
REFLECTION:

I gained my understanding of how lightbulbs (incandescent, halogen, and compact fluorescent (CFL)) work in Chem507 during an activity in which the cohort worked in small groups measuring the respective emission spectra and researching online.  Growth is shown by my increased understanding of how various lights work and how they differ from each other.  I know the components of a incandescent, halogen, and fluorescent light bulb and their roles. 

SUMMARY OF CONTENT:

Incandescent light bulbs. In an incandescent light bulb, a tungsten filament encased in a glass bulb filled with an inert gas is heated via electrical resistance until it glows, simultaneously producing a significant amount of thermal radiation (i.e. heat)--it is the least efficient lightbulb.

Halogen light bulbs. In a halogen light bulb, a tungsten filament encased in a quartz casing filled with a halogen gas is heated via electrical resistance until it glows.  Halogen gases also produce a significant amount of heat, but last longer and may burn hotter (and therefor glow brighter) because the quartz casing allows for higher temperatures and the halogen gas helps preserve the light filament by reacting with the vaporized tungsten and redepositing it upon the filament.

Compact fluorescent light bulbs. In a CFL, Hg gas is electrically stimulated to emit UV light, which is absorbed by a the phosphor coating, which effectively converts UV light to infrared radiation and white light.  The phosphor coating is often made of more than one type of phosphor to more closely approximate white light (it may have one phosphor that absorbs UV light and emits green light; it may have others that emit blue or red light after UV absorption).  Because light is produced by directly stimulating excitation (in which Hg atoms absorp and emit energy), less energy is expended to heat light filaments and less energy is given off as waste heat.  Fluorescent light bulbs, therefore, do not get as hot as incandescent or halogen bulbs.