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Rubric 4
Application of Scientific Concepts
Reflections in this rubric show growth in my ability to apply concepts and scientific principles to practical problems and/ or real- world situations. For this rubric I introduce three reflections:
Reflection1: Incandescence, Fluorescence and phosphorescence. chem. 507
Reflection2: Eh- PH Diagram: Why is it important to maintain high Eh in
drinking water. chem505.
Reflection3: DNA the master molecule of life Chem. 503
Reflection 1:
Incandescence, Fluorescence and phosphorescence. Chem. 507
Enduring Understanding: Understanding light and how light affects matter are paramount to understanding spectroscopy.
Absorption and emission of light as it relates to energy levels of atoms and molecules.
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Incandescent and Fluorescent light bulbs are very familiar to all and very much related to real world applications. Sixteen years ago I lived through two wars, two years apart and in each war, the first target to be bombed was the general electricity buildings of Baghdad. Electrical generators running on gasoline were our only option and with that we always used fluorescent light bulbs, they use less electricity than incandescent lights, they are longer lasting and energy saving lightings. According to Energy star, a US environmental protection agency, CFLs use up to 75 percent less energy (electricity) than incandescent light bulbs, and last up to 10 times longer. The growth in this reflection will show the electronic levels understanding of why incandescent bulbs were not preferred when comparing to fluorescent bulbs. It is usually completely unnoticed by the senses that all material bodies are constantly emitting and absorbing electromagnetic radiation that originates in the random thermal motion of the electrically charged particles that constitute matter.
When the matter is highly heated the radiation begins to become visible to the eye as a dull red glow, and may be sensed as warmth by the skin. Further heating rapidly increases the amount of radiation, and its perceived color becomes orange, yellow and finally white. This radiation is called heat radiation, or blackbody radiation.
1. Baseline Reflection
The evidence shown below is the first assignment from chem. 507. Followed by an assay demonstrating my understanding. As a group we used all the given terms to define the incandescence as a general term for heat-driven light emission which includes the simple case of blackbody radiation. This assignment demonstrates my baseline understanding of how incandescent light bulbs work.
First assignment from chem. 507
The essay below explains how the resistance heats the filament to a temperature where part of the radiation falls into visible spectrum. The major part of the radiation is emitted in the IR spectrum which is why incandescent light bulb is insufficient.
Light bulb demo (essay) 
The essay also shows my basic understanding of Fluorescent and Phosphorescent.
Fluorescent light gives more visible light for the same amount of electricity. CFL is a gas discharge lamp which uses Hg Vapor when excited by electrical current and produces UV light. UV light then excites phosphor coating to produce quantized visible light.
In Phosphorescent materials, valence electron jump to higher orbital and remain trapped for (millisecond to a day) eventually drops back and emits radiation and the result is sustained glow light that lasts (millisecond to a day).
2. Later Reflection
A blackbody is a theoretical object that is considered to be the simplest emitter of electromagnetic radiation. It absorbs all electromagnetic radiation falling onto it and thus reflects no radiation. The wavelengths of the radiation emitted by the body are related only to its temperature. Blackbodies are named so because at room temperature they emit mostly infrared radiation which has a lower frequency and longer wavelength than visible
light. They reflect no radiation, so they would appear black. As the temperature of a blackbody increases its emitted radiation increases in frequency while shortening in wavelength and begins to be perceived as visible light. Any object hot enough to emit visible light is said to incandesce, and the phenomenon of visible light emission due to high temperature is known as incandescence. Raising the temperature needs high electricity and thus high energy is consumed. The energy that is not used to create light is instead converted into heat energy. Incandescent bulbs therefore produce substantially more heat than CFLs for a given light output. This explains why it is preferred to use fluorescent light bulbs when using gasoline generator to save the energy. The evidence below proves this understanding. Full grade and complete understanding to questions #4 for the two types of spectra of light sources explaining how light is produced.
In Incandescent (term for heat- driven light emission which includes a simple case of blackbody radiation) light bulbs, the electric current passes through a thin filament, heating it until it produces light.
Chem. 507 October 18, 2008
What happens to molecules after they absorb radiation? Some reemit a photon almost immediately and return to ground electronic state. This process is called fluorescence. The absorption of light does not change the electron spin and therefore gives an excited state called a singlet; with one spin clockwise and one spin couter clockwise. Electrons are excited from ground state to one of the various vibration states in the excited electronic state. Collisions with other molecules cause the lost of vibration energy until it reaches the lowest vibration state of the excited electronic state. The molecule then drops down to one of the various vibrational levels of the ground state emitting photon in the process. As molecules may drop down into any of several vibration levels in the ground state, the emitted photons will have different energies, and thus frequencies. Analyzing those frequencies determines the structure of the different vibration levels. This discussion shows my growth in explaining this phenomenon. The evidence below is a Chem. activity 22 we used in Chem. 507 to master this understanding.
Next I will compare incandescent bulbs with fluorescent bulbs. The first is inefficient at producing UV light, since due to its blackbody spectrum, an incandescent light radiates less than 0.1% of its energy as UV light. While in fluorescent light electricity is needed to excite Hg to produce UV waves causing phosphor to fluoresce producing visible light (using less power for the same amount of light).
CFLs with UV generating phosphor are much more efficient than UV produced by incandescent bulbs, because the amount of UV light that the filament of the incandescent lamp produces is only a fraction of the generated spectrum.
Chem 507. ChemActivity22. Fluorescence.
A third type of light emission is called phosphorescence. This occurs much slowly, over a period of seconds or in some cases hours. To understand phosphorescence, we have to consider the spins of the electrons in the excited state. The excited electronic state here is called a triplet that has both spins up and by Hund's rule; this has lower energy than the singlet. The triplet state cannot be reached directly by absorbing light, there must be a small probability that an excited molecule will cross over to the triplet state as it undergoes collisions. Once there, it remains for a long time because an emission from a triplet state to a singlet ground state is very slow.
Chem 507. ChemActivity22. Phosphorescence.
What can I impart to my students?
Objects absorb, reflect, and radiate a form of energy known as electromagnetic radiation which can be visualized as waves of energy that travel through open space. Different wavelengths of electromagnetic radiation have different common names, for example, visible light has wavelengths roughly between 380 and 750 nanometers (nm). An object is blackbody if the radiation it emits into space originates completely from its temperature.
Incandescence: is the emission of visible light caused by its high temperature. The resistance heats the filament to a temperature where part of the radiation falls into visible spectrum.
The major part of the spectrum is emitted in the IR spectrum which is why incandescence light bulb is insufficient.
Fluorescent light bulbs give more visible light for the same amount of electricity.
Fluorescence spectroscopy is used in differentiating malignant skin tumors from benign.
In Phosphorescence compounds valence electron jump to higher orbital and remain trapped for
(Millisecond to a day) eventually drops back and emits radiation and the result is sustained glow light that lasts (Millisecond to a day).
Mostly of the information about the spin quantum number S=0 and S=1 state and super imposed exited state demonstrated in my last evidence above is my advanced knowledge which I could not use so far in my classroom for the level is beyond high school students I teach.
Reflection 2:
Eh- pH Diagram: Why is it important to maintain high Eh in drinking water. Chem. 505.
Enduring Understanding:
Thermodynamics of natural aqueous systems are largely empirical because of variable water chemistry based on presence or absence of oxygen. General thermodynamic principles regarding the relationship between oxidation/reduction potential Eh and pH in natural waters are based on empirical observations, but general principles can be developed using stability field diagrams.
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I know that reduction potential is the tendency of a chemical compound or an element to acquire electrons and thereby be reduced. I am applying this to why Lead was a problem in Washington DC drinking water to show the progress in understanding the importance in maintaining high Eh in drinking water.
- 1. Baseline Reflection:
My knowledge about Eh before taking Chem. 505 environmental chemistry was as
follows: Reduction potential is the tendency of a solution to gain or lose electrons
when it’s subject to change by adding new compound.
- If the solution has a higher (more positive) reduction potential than the compound added, then this solution will have the tendency to gain electrons to be reduced by the oxidizing compound that was added.
- If the solution has lower (more negative) reduction potential than the new compound added, then the solution will have the tendency to lose electron to be oxidized by the reducing new compound.
I walked into the pre-exam Chem. 505 Summer 2008 with this information. For my baseline evidence I present question number 30 from the pre-exam taken before srarting the course. I didn’t know the importance of maintaining high Eh in drinking water, as a matter of fact; I didn’t even know the reduction potential was given the Eh abbreviation.
Chem. 505. Pre-exam
In tying the understudy of maintaining high Eh in drinking water with why was Lead a problem in Washington DC drinking water and since I first heard about it in this environmental class, I present the power point slides below to show what was discussed in class about what the problem was and what were the proposals to solve it are.
In 2003, residents of the District of Columbia (DC) experienced an abrupt rise in lead levels in drinking water, which followed a change in water-disinfection treatment in 2001.
In trying to eliminate the "potentially carcinogenic by-products" of chlorine in tap water, chlorination was replaced with chloramination, three years later; hundreds of families with homes fitted with lead pipes in the District of Columbia were exposed to dangerously high lead levels. Unknown to scientists at the time, the chlorine in tap water served as a 'binder' for the lead pipes, keeping a certain amount of lead from dissolving in the water.
Chem.505. Problem and Proposed Solution
Power Point slides
- 2. Later Reflection
- Below I demonstrate my growth in this area followed by evidences taken from tests and reflections from Chem. 505 course. Listed below is a summary of new knowledge I gained by the end of class;
a. High Eh means mostly in oxidizing region, and for the Lead problem in Washington DC drinking water high EH kept PbO2 in solid stated.
b. Switching to chloramines from chlorine lowered the oxidization potential increasing the leaching of Lead from pipes.
c. In some situations when brass is connected to copper, it is the Cathodic and the copper is the anode.
That means the brass is protected and the Lead is not released into the water but when adding Chloramines brass became highly anodic and copper is now Cathodic. This helps the release of any Lead in brass pipes because it is being sacrificed. Also the galvanic corrosion persists for days increasing the leaching of Lead.
d. Free chlorine can reduce Lead solubility compared with waters with chloramines or oxygen as an oxidant.
My first later evidence includes the same question (number 30) from the pre-exam Chem. 505, but this time in the post-exam. I explained that high Eh has the most meaning in the oxidizing region, for the solid to stay in solubility region, and might dissolve at low Eh when suggesting stable pH.
Chem. 505. Post-exam
In my second evidence below, Red dots are the Eh after the disinfection with NH2C1 had begun, where PbO2 started to dissolve. Brass is anodic and copper is cathodic, dissolving brass fixtures and releasing lead contaminants. PbO2 is likely to be soluble in highly oxidation environment over the PH range of treated drinking water. When using Chloramines the oxidation potential of Washington DC water was lowered so water might dissolve PbO2 which will raise the contaminant, where in the past large amount of Chlorine were used, so the highly oxidizing water kept PbO2 stable and insoluble.
Eh Diagram after disinfecting with NH2C1
Washington proposed adding PO4-3 to increase PH to 9; this system can get the Lead below 15 ppb because it will convert Lead back to PbCO3 as shown in figure below. Next Ca (OH)2 is added to remove phosphate keeping the ORP value of 280mv and a PH of 7.8 to put the PbO2 back in the stability field. Slide below shows the blue dot where washington wants to get by adding PO4-3
Power point showing ORP desired value
Reflection 3
DNA the master molecule of life. Chem. 503
Enduring Understanding:
· Genetic information is encoded in the sequence of bases in the biopolymer deoxyribonucleic acid (DNA)
· DNA exists as a double helix in which complementary base pairs project toward the center of helix and hydrogen bond with each other.
· In cell division, replication of the DNA results from separation of the double helix into template strands and construction of complementary strands on each of these.
· The genetic code is a three- letter code in which a sequence of three bases in DNA is transcribed into a sequence of three bases in ribonucleic acid (RNA) that is then translated into an amino acid subunit of a peptide or protein.
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Chem 503 class of April 26, 2008 covered nucleic acids related to the Enduring Understanding described above. DNA is the concept I chose to show growth in applying conceptual and science content learning to real life. Within the nucleus of each cell is chromatin, which consists of DNA surrounded by protein known as histones. Chromatin of any organism is organized into certain number of chromosomes (46 for humans).
DNA in a chromosome consists of many genes which contains information needed for synthesis of a single protein. DNA is a polynucleotide consists of three connected component: 2 deoxy-D-ribose sugar, a base, and a phosphate group.
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1. Baseline Reflection
Chem. 503 Problem Set # 8, question 3c and 3d.
This problem set is my baseline evidence because it was due before the beginning of class and it demonstrates my understanding based on the readings and the overviews Dr. Roberts provided for us before coming to class. The DNA in chromosomes forms the basis for the genetic code. It alone can determine how a cell operates and also all of our characteristics.
DNA is made of long chains of nucleotides as drawn in question 3c below. The nucleotide as drawn in the figure is made of three parts: 1. a phosphate group - helps form the backbone of the DNA molecule
2. a sugar (deoxyribose) - acts as a glue, forms the backbone with phosphate
3. Nitrogen bases - 4 types (guanine, cytosine, adenine, thymine)
DNA has a double-helix structure where two strands of nucleotides join and twist around to form a spiral staircase or twisted ladder. It was important to learn the structure of those four nitrogen bases because, as this will be explained in the later reflection, the structure will affect the melting points of both DNA and RNA and eventually the stability of those macromolecules. DNA tirnucleotide T-G-C is drawn blow.
Chem. 503 Problem Set # 8, question 3c.
Chem. 503 Problem Set # 8, question 3d. RNA trinucleotide A-U-G is drawn below. Uracil appears only in RNA and can only make two H-bonds.
Chem. 503 Problem Set # 8, question 3d
The following is the foundation I chose to have as a reference when teaching DNA in my biology class.
2. Later Reflection
DNA is made of long chains of nucleotides. Each nucleotide has 3 parts: 1. a phosphate group - helps form the backbone of the DNA molecule
2. a sugar (deoxyribose) - acts as a glue, forms the backbone with phosphate
3. nitrogen bases - 4 types (guanine, cytosine, adenine, thymine)
the base of one nucleotide forms a hydrogen bond with the base of another nucleotide, thus the bases form the steps of the DNA ladder. the sequence of the bases makes up the genetic code Adenine and guanine are purines in DNA, these bases form hydrogen bonds with their complementary pyrimidines; thymine and cytosine respectively. Adenine and thymine always bind to one another (A-T). Cytosine and guanine bind together (C-G). This is called the complementary base paring.
I grew in learning to draw structures showing H-bonding between uracil and adenine in RNA and comparing it with that of thymine and adenine in DNA. This is demonstrated in the figure shown below. Quiz eight. question 8. They both have the same number of H- bonds. Uracil in RNA and thymine in DNA can make only two H-bonds.
Chem. 503. Quiz eight. question 8.
I also grew in learning to explain the stability of DNA due to the extra H-bond between its guanine, and cytosine (G/C) nitrogen bases. Question seven from quiz 8 of the second evidence below explains the stability of DNA double helix measured by its melting point. The high melting point is due to the third H-bonding between G/C.
Chem. 503. Quiz 8. Qestions seven.
The last later evidence I present the book review project from organic chemistry 503. I wrote about James Watson and Francis Crick whom discovered the DNA as a double helix in which two strands of DNA coil around each other.
What can I impart to my students? 1. Nucleotides are molecules when joined together make up the structural unites of DNA and RNA.
2. Chemical energy stored in adenosine triphosphate and guanosine triphosphate.
3. Nucleotide are made of sugar, a nitrogen base, (adenine, guanine, thymine, and cytosine, and uracil is the nitrogen based found in RNA), and the third component of nucleotide is the phosphate group (energy source).