#08 Forensic and Commercial Applications of Interactions ...terrificscience.org/lessonpdfs/RadiantEnergy.pdf · #08 Forensic and Commercial Applications of Interactions Between Radiant

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#08 Forensic and Commercial Applicationsof Interactions Between Radiant Energy and MatterDiane Krone, Northern Highlands Regional High School, Allendale, NJ 07401

Outline of Unit

1. Nature of Spectra

Students are given a quantitative spectroscope. They will use this to observe the spectra ofsunlight, an incandescent light bulb, fluorescent light, and a hydrogen gas discharge tube. Thestudents will learn how to read the wavelengths on the spectroscope’s scale. They will alsocompare spectral bands with spectral lines.

2. Element Identification by Emission Spectra

Students will examine the spectral lines from a mercury gas discharge tube and they will look forsimilarities in these spectral lines to those of the fluorescent light. The term emission spectrumwill be discussed. Students will then perform some flame tests on salts of sodium, calcium,potassium, copper, lithium, and strontium. They will then be given several unknowns to identifyin order to reinforce the “fingerprinting” concept.

3. Absorption Spectra

As a demonstration of absorption spectra, 2 grams of erbium chloride (Alpha Chemical) isdissolved in 20 mL water. The solution is placed in a large test tube and the test tube is held infront of a glowing aquarium light. The students will observe the black lines associated with anabsorption spectrum. The flame test for erbium chloride will be performed so students cancompare an absorption spectrum with an emission spectrum.

4. The Relationship Between the Atomic Spectrum of Hydrogen and the Bohr Model

This worksheet has the students calculate the energy transitions associated with the spectral linesof hydrogen and relate these energy transitions to quantum numbers. Sample spreadsheets areincluded.

5. Using Raman Spectroscopy in Forensic Chemistry

In this activity, students calculate the vibrational bond energies of some common bonds andrelate their findings to Raman absorption spectra of real and fake gemstones. You may be able tomake arrangements with a local university to have your students actually perform the tests.Spectra from several samples are included for student interpretation.

6. Rediscovering the Cyanotype Process

Energy from electromagnetic radiation can be transferred to a molecule and produce a chemicalreaction. Some interesting and important photochemical reactions include photography,

To close the yellow note, click once to select it andthen click the box in the upper left corner.To open the note, double click (Mac OS) or rightclick (Windows) on the note icon.

The Center for Chemical Education

This activity has been peer reviewed but not field tested. Try the activity yourself before using it with students. This document was designed to be distributed electronically and then printed on a laser printer on an as-needed basis. For this reason, the fonts and layout of this document have been chosen for optimal printing rather than for optimal viewing on-screen. To review this document on-screen, however, simply increase the magnification using the magnification box at the bottom of the window. You may select the text and graphics in this document and copy them to the word processor of your choice.

Collection of Laboratory Activities: Activity 8


photosynthesis, production of photochemical smog, photoelectrolysis, and the tanning of skin. Inthis activity, students will examine a commercial application of the photochemical process andproduce a cyanotype photogram.



Nature of Spectra

INTRODUCTION

DescriptionStudents will use quantitative spectroscopes to compare the spectra of sunlight, an incandescentlight bulb, fluorescent light, and a hydrogen gas discharge tube. They will associate colors oflight with their wavelengths. They will be able to explain why sunlight, when viewed through aspectroscope, produces spectral bands and fluorescent light produces spectral lines.

Student AudienceThis activity is suitable for Chemistry I students and serves as a review for Chemistry II and A.P.Chemistry students.

Goals for the Activity• To understand the relationship between color of light and wavelength.

• To identify sources of continuous and bright line spectra.

• To compare a continuous spectrum with a line spectrum.

Recommended Placement in the CurriculumAtomic Theory



Nature of Spectra

Purpose

After completing this activity you will be able to associate a wavelength of light with its color, toidentify sources of continuous and bright line spectra, and compare a continuous spectrum with aline spectrum.

Introduction

In the seventeenth century, Sir Isaac Newton used a prism to show that white light from the suncontains many color components. The continuous spectrum he observed contained all thewavelengths of light between 400 and 700 nm. In 1859 Robert Bunsen and Gustav Kirchhoffbuilt a spectroscope to study the light emitted when various salts were added to a flame. Theyobserved line spectra instead of a continuous spectrum. Line spectra are light emissions only atspecific wavelengths. These lines consist of light of discrete energies. It wasn’t until early in thiscentury that the origin of these lines were discovered. Ordinarily, the electrons in an atom are intheir lowest or ground state. When an electron absorbs enough energy, it moves to an excitedstate. The excess energy is them emitted as radiant energy of a particular wavelength.

These websites and their links will give you more information on light, continuous spectra andline spectra (These websites were last accessed in July 1998):

http://encyclopedia.com/printable/12199-a.html

http://www.csun.edu/~hchum001/bookcase/light/spectrum.html

http://scienceweb.dao.nrc.ca/astro/hia/spectrum/sintro1.htm

Light Observed Through a Spectroscope

1. Your teacher will give you a quantitative spectroscope. View the sunlight through yourspectroscope. Caution: Do not look directly at the sun. In the box below record the colors oflight you observe and the wavelengths associated with each color.

2. Use your spectroscope to view the incandescent light bulb. In the box below record the colors oflight you observe.

3. Look at a fluorescent light bulb through your spectroscope and record your observations.

4. Your teacher has set up a hydrogen gas discharge tube. View this light through your spectroscopeand record your observations.



Observations

400nm 500nm 600nm 700nm

Figure 1. Sunlight

400nm 500nm 600nm 700nm

Figure 2. Incandescent Light

400nm 500nm 600nm 700nm

Figure 3. Fluorescent Light

400nm 500nm 600nm 700nm

Figure 4. Hydrogen Gas Discharge Tube



Questions

1. What is the difference between a continuous spectrum and a bright line spectrum?

2. Why did the incandescent bulb produce a continuous spectrum while the fluorescent lightproduced a line spectrum?

3. When you observed the hydrogen spectrum, you saw bright lines between black spaces. Why arethe black spaces present?



INSTRUCTOR NOTESNature of Spectra

Time Required45 minutes

Group SizeStudents can work individually or in pairs.

Materials Needed

• Class set of Quantitative Spectroscopes (from Flinn Scientific)• Fluorescent light bulb• Incandescent light bulb• Spectrum tube power supply (Flinn Scientific)• Hydrogen spectrum tube

Points to Cover in the Pre-Activity Discussion

Before students begin this activity, introduce the electromagnetic spectrum and discuss thenature of light waves.

Procedural Tips and Suggestions

While each student is able to view the spectra individually, it is a good idea to discuss theirobservations as a class group. This guarantees that all students are making correct observationsand can interpret their results.

Sample Results

(from: http://www.csun.edu/~hchum001/bookcase/light/spectrum.html; downloaded in July 1998)



Incandescent Light

Hydrogen Spectrum

Plausible Answers to Student Questions

1. Continuous spectra contain all wavelengths while line spectra contain specific wavelengths oflight.

2. In the incandescent bulb a solid is glowing, and many energy transitions are occurring. Thefluorescent bulb contains gases.

3. These black areas are dark areas where no light is being emitted.



Element Identification by Emission Spectra

INTRODUCTION

Description

In this activity, students observe the color of the flame and the spectral lines of known salts todevelop “fingerprints” of the samples. They use this information to identify unknown samples.

Student Audience

This activity is suitable for Chemistry I students and serves as a review for Chemistry II and A.P.Chemistry students.

Goals for the Activity

• To observe flame colors and spectral lines.• To create “fingerprints” of known samples of salts.• To use the “fingerprints” to identify unknown samples.

Recommended Placement in the Curriculum

• Atomic Theory and Emission Spectra• Analytical Chemistry



STUDENT HANDOUTElement Identification by Emission Spectra

Purpose

After completing this activity you will understand how an element can be identified by its“spectral fingerprint,” and you will be able to perform the flame test to identify unknown salts.

Introduction

In the last activity you observed that hydrogen atoms in a discharge tube produced bright lines indifferent parts of the visible spectrum. Hydrogen gas will always produce the same emissionspectra and every element has its own emission spectrum. The characteristic lines in atomicspectra can be used to identify unknown atoms. Thus, each element has its own set of“fingerprints.”

Two websites (last accessed in July 1998) to help you explore this concept are:

http://chico.ncsa.uiuc.edu/Cyberia/Bima/CBCSpecLines.html

http://brianjones.ctss.colostate.edu/CD_Spectroscope.html

Element Identification by Emission Spectra

1. Look at a mercury gas discharge tube through the spectroscope and observe the green and purplelines. A fluorescent light bulb contains mercury vapor. Observe the light from a fluorescent bulband look for the green and purple lines you observed previously. The unique lines of the mercuryemission are the bright green and purple lines, and this is referred to as its “fingerprint.”

2. You will be provided with spray bottles that contain dilute solutions of known salts. Have yourpartner spray a small amount of a solution into the flame of a Bunsen burner while you view thelines with your spectroscope. Record the color of the flame you observed with the naked eye andthe most dominant spectral lines when viewed through the spectroscope. Repeat this procedurefor each salt solution.

3. Place a small piece of banana on the end of a spatula. Place this in the Bunsen burner flame andobserve the spectral lines. What element can you identify?

4. Dip a clean spatula into some chicken soup and perform a flame test. What element can youidentify?

5. Your teacher will give you two unknown solutions. Perform the flame test on these unknownsand identify the elements present.



Results

stseTemalFrofstluseR:1elbaT stseTemalFrofstluseR:1elbaT stseTemalFrofstluseR:1elbaT stseTemalFrofstluseR:1elbaT stseTemalFrofstluseR:1elbaT

tlaS emalFforoloC tnanimoDseniLlartcepS

edirolhcmuidoS

edirolhcmuiclaC

edirolhcmuissatoP

edirolhcmuihtiL

edirolhcmuitnortS

edirolhc)II(reppoC

snwonknUgniyfitnedI:2elbaT snwonknUgniyfitnedI:2elbaT snwonknUgniyfitnedI:2elbaT snwonknUgniyfitnedI:2elbaT snwonknUgniyfitnedI:2elbaT

elpmaS tneserPtnemelE

ananaB

puosnekcihC

1noituloS

2noituloS



INSTRUCTOR NOTESElement Identification by Emission Spectra


Group SizeStudents work in pairs.

Materials Needed• Spray bottles (emptied and washed hair spray bottles) filled with dilute salt solutions• Salt solutions:

§ sodium chloride§ calcium chloride§ potassium chloride§ lithium chloride§ strontium chloride§ copper(II) chloride

• Banana• Canned chicken broth (not reduced sodium)• Bunsen burners


Define spectral lines and make the comparison between human fingerprinting and spectral“fingerprints.”

Procedural Tips and Suggestions

1. Prepare dilute solutions of the salts to be tested and place them in labeled hair spray bottles.

2. Establish testing stations around the room. Have students move to each testing station observingthe flame color and bright line spectra.

3. The students are expected to use their data to identify the unknowns. One of the unknownsolutions may be any of the salt solutions while the second can be a mixture of two of the saltsolutions.

Sample Results

tlaS emalFforoloC

edirolhcmuidoS wolleY

edirolhcmuiclaC der-egnarO

edirolhcmuissatoP teloiV

edirolhcmuihtiL deR

edirolhcmuitnortS nosmirC

edirolhc)II(reppoC neerG

elpmaS tneserPtnemelE

ananaB muissatoP

puosnekcihC muidoS



TEACHER DEMONSTRATION

Absorption Spectra


Goals• To demonstrate absorption spectra.• To compare an absorption spectrum with an emission spectrum.

Materials Needed

• Large test tubes filled with solutions of:§ Green food coloring§ Blue food coloring§ Orange food coloring§ Red food coloring

• Erbium chloride (2 grams is dissolved in 20 mL water)• Solid erbium chloride• Aquarium light• Bunsen burner• Class set of qualitative spectroscopes

Procedure

1. Turn on the aquarium light and place a test tube filled with the green solution in front of thelight. Allow the students to observe the absorption spectrum. Absorption will occur in the redrange and a black band will be observed in this region of the spectrum. Red is the complimentarycolor of green.

2. Continue viewing the other colored solutions. Yellow is complementary to blue; red to cyano;orange to blue cyan.

3. Place the test tube that contains the erbium chloride in front of the light. Allow the students toobserve the absorption spectrum.

4. Perform a flame test using the solid erbium chloride. The black lines of the absorption spectrumand the bright lines of the emission spectrum should be evident.

Points to Cover in the Discussion

• The colored solutions will transmit their color and absorb complimentary colors. For example,the orange solution will show a black band in the blue region.

• Students who have taken art courses will be able to identify complimentary colors.• After the students observe the absorption spectrum for the erbium salt, have them predict what

the emission spectrum will look like.



The Relationship Between the Atomic Spectrum of Hydrogenand the Bohr Model

INTRODUCTION

Description

Students will calculate the energy transitions associated with the spectral lines of hydrogen andrelate these energy transitions to quantum numbers through the use of a spreadsheet.

Student Audience

This activity is suitable for Chemistry II and A.P. Chemistry students.


• To relate wavelength, frequency, and energy.• To use the Bohr model to identify lines in the hydrogen spectrum.• To find similarities between Balmer’s formula and Bohr’s.• To use the spreadsheet as an analytical tool.


Atomic Theory



STUDENT HANDOUTThe Relationship Between the Atomic Spectrum of Hydrogen and

the Bohr Model

Purpose

After completing this activity you will be able to relate the observed spectral lines for thehydrogen atom with the theory that describes the energy transitions as the hydrogen atom’selectron falls from excited states to the ground state.

Introduction

One of the simplest of atomic spectra is that of hydrogen. The hydrogen emission spectrum iscalled a line spectrum, with each line corresponding to a discrete electromagnetic wavelength.The line spectrum indicates that only certain energies are allowed for the electron in thehydrogen atom and we say that the electron energy levels are quantized. If any energy level wereallowed, the emission spectrum would be continuous, like that of white light.

Knowing the wavelength of a spectral line, we can calculate the change in energy from a high toa lower energy level by using Planck’s equation:

E = h = hc / (1)

h 6.626x10 J s frequency(Hz)

c 3.00x10 m / s wavelength(nm)

34

8

υ λυ

λ= ⋅ == =

−

In 1913, Neils Bohr, a Danish physicist, derived a theoretical explanation of the atomic spectrumof hydrogen. Ordinarily the hydrogen electron is in the first energy level. We say that theelectron is in its ground state, and n = 1. When an electron absorbs enough energy, it moves to ahigher, excited state. When an excited electron drops back to a lower energy state, it gives offenergy as a photon of light, which we observe as a spectral line. With the equations below, it ispossible to relate the principle quantum numbers with the frequency of light emitted:This interactive website contains more information about the Bohr atom:

E = h = E E (2)

E = h = -R 1/ (n ) 1 / (n ) (3)

R 2.180 x 10 J n = energy level of electron

hi lo

H hi2

lo2

H18

υ

υ

−

−[ ]= −

http://efnt1.fedu.metu.edu.tr/thinkque/hydro.htm (last accessed in July 1998)

The spectral lines of hydrogen

Using the data below, create a spreadsheet which can calculate the energy associated with eachspectral line.



motanegordyhehtfosenillartcepsfo)mnni(htgnelevaW motanegordyhehtfosenillartcepsfo)mnni(htgnelevaW motanegordyhehtfosenillartcepsfo)mnni(htgnelevaW motanegordyhehtfosenillartcepsfo)mnni(htgnelevaW motanegordyhehtfosenillartcepsfo)mnni(htgnelevaW

teloivartlU)seireSnamyL(

elbisiV)seireSremlaB(

derarfnI)seireSnehcsaP(

35.121 82.656 90.5781

45.201 31.684 08.1821

32.79 50.434 08.3901

59.49 81.014 39.4001

57.39 10.793

50.39

The Bohr model of the atom

Using the formulas given above, develop a spreadsheet which can calculate the frequency andwavelength associated with all the possible energy transitions that an excited electron in theseventh energy level of the hydrogen atom can undergo.

The Bohr model relates to the spectral lines of hydrogen.

Use the two spreadsheets you developed to compare the wavelengths of the atomic emissionspectrum of hydrogen to the wavelengths associated with the electronic energy transitions.

Related Questions

1. Equation (3) in the introduction is arranged so that ∆E (or hυ) will always be a positive value.Why is this important?

2. What are the energy transitions associated with the Balmer series?

3. What are the energy transitions associated with the Lyman Series?

4. What are the energy transitions associated with the Paschen Series?

5. There are five distinct emission lines of visible light in the Balmer Series. Identify the color oflight associated with each spectral line.

υ = C(1/ 2 1 / n )2 2−

6. In 1885, a Swiss schoolteacher named Johann Balmer observed that the frequencies of the fivelines of visible light from the hydrogen fit an intriguingly simple formula:

In this formula, C is a constant equal to 3.29 x 1015 s-1. Explain how this formula relates toBohr’s formula. Multiply C by Planck’s constant. What value do you get?



INSTRUCTOR NOTESThe Atomic Spectrum of Hydrogen


Group SizeStudents work best individually or in pairs.

Materials NeededEach team will need access to a computer with a spreadsheet program.

Points to Cover in the Pre-Activity DiscussionBefore students begin this activity, have them observe the spectral lines of the hydrogen atom. Ifyour school does not have the equipment for this observation, you may be able to borrow thesupplies from a local college. As a last resort, students can observe pictures of the atomicspectrum of hydrogen.

Procedural Tips and SuggestionsEquation (3) is arranged so that ηυ will be a positive value. You may want to mention to thestudents that from a thermodynamics point of view, since electrons are losing energy, ?Ε shouldbe a negative value. But, if we follow this bookkeeping strategy, the frequency will have anegative value and that doesn’t make sense.

Sample Results

A sample spreadsheet that calculates the wavelengths of light associated with the possibleelectronic transitions and between wavelength and the energy of the electron is included.


1. A negative value would indicate a negative value for frequency.

2. The spreadsheet shows that transitions from excited states to n = 2 are associated with the Balmerseries. These transitions result in the spectral lines observed in the pre-activity discussion.

3. The spreadsheet shows that transitions from excited states to n = 1 are associated with the LymanSeries.

4. Transitions to n = 3 are associated with the Paschen series.

5.htgnelevaW

)mn( roloC

656 der

684 neerg

434 eulb

014 ogidni

793 teloiv



6. The Balmer series is a result of energy transitions to n=2. That accounts for his equationincluding 1/22. The value is equal to the Rydberg constant.

Extensions and Variations

Students can create a spreadsheet that will calculate the ionization energy for various atoms andions. Equation (3) will be modified as:

E h R z / (n )H2

ground2= = − [ ]υ

z = atomic number. The ionization energy of the H atom, He+, and Li2+ can be compared.

References

Masterson, William L., Hurley, Cecile N. Chemistry Principles and Reactions; Harcourt Brace: NewYork, 1993, pp 130-136.

Chang, Raymond. Chemistry; McGraw-Hill: New York, 1998, pp 246-254.



Electronic transitions in the Bohr model for the hydrogen atom.

This sample spreadsheet calculates the wavelengths of light associated with possible electronictransitions for the hydrogen atom.

motAnegordyHehtrofledoMrhoBehtnisnoitisnarTcinortcelE motAnegordyHehtrofledoMrhoBehtnisnoitisnarTcinortcelE motAnegordyHehtrofledoMrhoBehtnisnoitisnarTcinortcelE motAnegordyHehtrofledoMrhoBehtnisnoitisnarTcinortcelE motAnegordyHehtrofledoMrhoBehtnisnoitisnarTcinortcelE

noitisnarT ycneuqerF)s/l(

-gnelevaW)mn(ht

shtgnelevaW)J()mn(

ygrenEegnahC

morF oT teloivartlU)seireSnamyL(

2 1 51+E74.2 85.121 35.121 81-E46.1

3 1 51+E29.2 85.201 45.201 81-E49.1

4 1 51+E80.3 62.79 32.79 81-E40.2

5 1 51+E61.3 89.49 59.49 81-E90.2

6 1 51+E02.3 97.39 57.39 81-E21.2

7 1 51+E22.3 80.39 50.39 81-E41.2

remlaB(elbisiV)seireS

3 2 41+E75.4 25.656 82.656 91-E30.3

4 2 41+E71.6 13.684 31.684 91-E90.4

5 2 41+E19.6 12.434 50.434 91-E85.4

6 2 41+E13.7 33.014 81.014 91-E58.4

7 2 41+E55.7 51.793 10.793 91-E10.5

nehcsaP(derarfnI)seireS

4 3 41+E06.1 77.5781 90.5781 91-E60.1

5 3 41+E43.2 72.2821 8.1821 91-E55.1

6 3 41+E47.2 02.4901 8.3901 91-E28.1

7 3 41+E89.2 03.5001 39.4001 91-E89.1

5 4 31+E04.7 06.2504

6 4 41+E41.1 80.6262

7 4 41+E83.1 03.6612

6 5 31+E20.4 74.0647

7 5 31+E54.6 61.4564

7 6 31+E24.2 09.27321



Using Raman Spectroscopy In Forensic Chemistry

Introduction

Description

In this activity, students calculate the vibrational bond energies of some common bonds andrelate their findings to Raman absorption spectra of real and fake gemstones. Spectra fromseveral samples are included for student interpretation.You may be able to make arrangements with a local university to have your students actuallyperform the tests.

Student Audience

This activity is suitable for Honors Chemistry I, Chemistry II, and A.P. Chemistry students.


•To understand how Raman spectroscopy can be used to determine molecular structure.

• To apply Raman spectroscopy to a forensic case study.

• To use the spreadsheet as an analytical tool.


• Molecular structure and bond energy

• Forensic chemistry



Using Raman Spectroscopy In Forensic Chemistry

PurposeAfter completing this activity you will have an understanding of the theory behind Ramanspectroscopy and be able to apply the principles to solve a forensic case study.

IntroductionWhen photons interact with matter they may be absorbed, emitted, or scattered. You haveobserved the first two phenomena in previous activities and we will now focus on whathappens when radiation is scattered. If the incident light elastically collides with the sampleand there is no energy change, the scattered light remains the same wavelength as theincoming light. But let’s look at a second scenario when the incident light inelasticallycollides with the molecules. This causes the vibrational energy of the molecules to change.The vibrational energy may either increase or decrease. In turn, the scattered light is of adifferent energy, frequency, and wavelength than the incident light. This is called Ramanscattering.

Now refer to these web sites to reinforce this explanation:

http://www-personal.umich.edu/~jshaver/virtual/labeled/explain.html

http://www.lafayette.edu/faculty/waltersv/ramansp.htm

To visualize the vibrational energies of molecules connect to:

http://www.haverford.edu/chem/physchemweb/ccl4.html#tutorial

Refer to this site to learn about the various components of the instrument used in Ramanspectroscopy:

http://www-personal.umich.edu/~jshaver/virtual/labeled/schematic.html

(All websites were last accessed in July 1998.)

Of the three vibrations you just observed, stretching (the A1 mode) is most often used todetermine molecular structure. You can calculate stretching frequencies of the bonds byapplying Hooke’s law. Just imagine the oscillating motion two atoms joined by a springwould have.

cm = 1

2 c

f

MxMy

Mx + My

-1

Π

12

cm-1 = absorbed vibrational frequencyc = speed of light (2.99 x 1010 cm/sec)f = force constant of bond (475,000-640,000 dynes/cm)Mx and My = mass (g) of atoms X and Y



Activity 1

Using the equation on the previous page, develop a spreadsheet that calculates the absorbedvibrational frequency (stretching frequencies) ranges for each bond below:

carbon - hydrogencarbon - oxygencarbon - chlorinesilicon - oxygencarbon - carboncarbon - deuterium

You will be given Raman spectroscopic scans for chloroform (CHCl3); deuterochloroform

(CDCl3); calcium carbonate (CaCO

3); and diamond.

Using your data from the spreadsheet, identify the bond for as many peaks as you can on each ofthe scans.

Questions and Discussion

1. Describe an inelastic collision.

2. Draw a diagram that demonstrates the energy transfers that result in Raman scattering.

3. According to the data in your spreadsheet, what happens to the vibrational frequency as the massof the atoms increases? What evidence do you have to support your answer?

4. How do the observed frequencies in your scans compare to your calculated frequencies in yourspreadsheets?

5. Using Raman spectroscopy describe how you would be able to tell the difference between a realdiamond and an artificial diamond composed of zirconium silicate (ZrSiO

4).

Activity 2

Part A

John wants to surprise his girlfriend with a large engagement ring for Valentine’s Day.Because John doesn’t have much money, he reads the advertisements in the paper looking fora jewelry sale. He finally sees an add that is too good to be true. So he rushes to the jewelrystore for his diamond. While John may not have much money, he makes up for it inintelligence. His best friend is an analytical chemist; so after paying a small down paymentfor the ring, he brings it to his friend who runs a Raman spectrum. Look at the scan andadvise John about purchasing that ring for his girlfriend.



Part B

You just purchased a jewelry store. Now you must fill it up with jewels and gems. So, yourush over to the jewelry exchange in the city to look for good buys, but you are new to thebusiness and don’t know who to trust. Thank goodness you know John, because he tells youabout this simple, non-evasive test you can perform on your diamonds and pearls to test theirauthenticity. After looking at your Raman spectra for the diamond ring and pearl earringsyou just purchased, can you charge top dollar for them? How can you convince yourcustomers to do business with you?

Further Information

Visit these websites (last accessed in July 1998) to obtain more information about theory andthe history of Raman Spectroscopy:

http://www.nicolet.com/theory.html#Raman

http://www.nicolet.com/Raman_History.html

http://www.andor-tech.com/raman_overview.html

http://aluminum.sem.arizona.edu:8001/outreach/demos/RAMAN.html

http://www.namar.com/



Using Raman Spectroscopy For Forensic Chemistry

Instructor Notes

Time Required: three 45-minute class periods

Group Size: Teams consist of two members.

Materials Needed: Each team will need:

Internet access (optional) ComputerRaman spectral graphs Spreadsheet program


Remind students that spreadsheet calculations will give them the theoretical range ofvibrational frequencies for each bond. This data will be compared to actual Raman spectra.

Sample Results

A sample spreadsheet is included at the end of this section.


Activity 1

1. An inelastic collision is one in which there is an energy transfer.

2.

(from: http://www.lafayette.edu/faculty/waltersv/ramansp.htm; downloaded on July 8, 1998)



3. Mass and vibrational frequency are inversely proportional to one another. The evidence for thiscan be seen by comparing the vibrational frequencies between the C-H and C-D bonds.

4. The C-H bond can be found on the CHCl3 spectral scan and can be located at around 3100 cm-1.

This corresponds to the calculated vibrational frequency for this bond. The C-O bond can befound on the CaCO

3 spectral scan. The vibrational frequency for this bond can be seen at about

1100 cm-1. This value also corresponds to the calculated vibrational frequency. Hooke’s lawgives a good estimation vibrational frequency.

5. A real diamond is composed of carbon. If the sample is a real diamond, I would expect to find apeak in the 1163 cm-1 to 1350 cm-1 range in the Raman spectrum. On the other hand, if thesample is that of zirconium silicate, a peak will appear at about 1000 cm-1.

Activity 2

Sample A is the artificial pearl, while sample B is the genuine pearl.

Sample C is the real diamond and sample D is the artificial diamond.

Extensions and Variations

After students understand how Raman spectroscopy can be used to identify chemicals, thisactivity can be extended to include infrared (IR) spectroscopy. IR spectra can be found on theinternet. The teacher can create a packet of known samples for students to study. They canthen identify unknown structures.

References

Parker, Sybil P., Ed. McGraw-Hill Encyclopedia of Chemistry; McGraw-Hill: New York,1993, pp 941-945.

Willard, Hobart H., Merritt, Lynne L., Dean, John A., Settle, Frank A. Instrumental Methods ofAnalysis; Litton: Belmont, 1981, Chap 8.

Aponick, A.; Johnston, C.; Marchozzi, E.; Wigal, C.T.J. Chem. Educ. 1998, 75, 465.



Absorbed Vibrational Frequencies Using Hooke’s Law

Teacher’s NotesUsing Raman Spectroscopy In Forensic ChemistrySample Spreadsheet

XssaMraloM XssaMraloM XssaMraloM XssaMraloM XssaMraloM YssaMraloM YssaMraloM YssaMraloM YssaMraloM YssaMraloM

dnoB )lom/g( )g(xM )lom/g( )g(yM

H 21 32-E99.1 1 42-E66.1

O-C 21 32-E99.1 61 2 32-E66.

lC-C 21 32-E99.1 5.53 5 32-E09.

O-iS 82 32-E56.4 61 2 32-E66.

C-C 21 32-E99.1 21 32-E99.1

D-C 21 32-E99.1 2 3 42-E23.

dnoB muminiMtnatsnocecrof

mumixaMtnatsnocecrof

muminiMlanoitarbiV

ycneuqerF)mc/1(

mumixaMlanoitarbiV

ycneuqerF)mc/1(

H-C 5+E57.4 5+E04.6 4692 1443

O-C 5+E57.4 5+E04.6 8801 2621

lC-C 5+E57.4 5+E04.6 159 4011

O-iS 5+E57.4 5+E04.6 298 6301

C-C 5+E57.4 5+E04.6 3611 0531

D-C 5+E57.4 5+E04.6 5712 5252

Key1/cm = absorbed vibrational frequencyc = speed of light (2.99 x 1010 cm/sec)f = force constant of bond (475000-640000 dynes/cm)Mx and My = mass (g) of atoms X and Y



















Light Activated Reaction

Teacher Demonstration

Time Required: 20 minutes

Goal:

• To introduce a photochemical reaction

Materials Needed

1 thick walled test tube (Pyrex #9860) 2 wires with alligator clips 1 cork to fit the test tube 1 9-volt battery 1 ping pong ball 110 camera with flash 1 bulb cut from a Samco #234 pipet 1 ring stand with test tube clamp 1 Beral pipet with tip cut off concentrated HCl 2 graphite rods from BIC pencil 1 orthodontic rubber band hot-melt glue gun and glue

Procedure

Step 1: Collection of H2 and Cl2 gases

The above diagram shows the setup for collection of gases. The tip is cut off of a Beral pipet andtwo holes are made at the top of the pipet using a straight pin. The carbon leads are placed ineach of these holes. They can be held in place by an orthodontic rubber band.

The pipet is filled

with concentrated HCl. The bulb is cut off of a Samco #234 pipet and a hole is made at the

bottom so that this sits on top of the Beral pipet. A test tube filled with water is inverted into this

pipet. Using alligator clips, the leads are connected to a 9-volt battery. This generates the two

gases. The gases are collected into the test tube by water displacement.



Step 2. The reaction

Using a hot glue gun, the ping pong balled is attached to the cork. A smiling face is drawn on theping pong ball. This adds character to the demonstration.

When the test tube is completely filled with the gases it is removed from the holder and is

stoppered with the cork. The test tube is placed in a plastic holder that is attached to a ring stand

with a test tube clamp. The plastic holder is the plastic container that the florist puts on the end of

roses to hold a few cc’s of water. This is done for safety reasons; the container acts as a cushion

for the test tube. Use a flash camera to “take a picture” of the test tube. The cork flies out of the

test tube and the character takes a trip.



The reaction that has taken place is:

H Cl 2HCl2 2+ →

This is a multistep reaction in which the first step requires light.

Step 1: Cl 2Cl

Followed by: Cl + H HCl + H

H + Cl HCl +Cl

2

2

2

h υ ⋅ → ⋅

⋅ → ⋅

⋅ → ⋅

HH +Cl HCl⋅ ⋅ →

Points to Cover in the Discussion

• The light energy from the flash activates the chemical reaction.

• Ask students to identify other examples of photochemical reactions. They should identifyphotosynthesis and the exposure of film to light as two examples.

Safety

Wear safety goggles, acid-resistant gloves, and a lab apron.Fill the Beral pipet with hydrochloric acid in a fume hood.

Disposal

Follow disposal procedure #24b from the current Flinn Chemical Catalog.



Rediscovering the Cyanotype Process

Introduction

Description

Energy from electromagnetic radiation can be transferred to a molecule and produce achemical reaction. Some interesting and important photochemical reactions includephotography, photosynthesis, production of photochemical smog, photoelectrolysis, and thetanning of skin. In this activity, students will examine a commercial application of thephotochemical process and produce a cyanotype photogram.

Student Audience

This activity is suitable for Chemistry I, Chemistry II, and A.P. Chemistry students.

Goals for the Experiment

• To understand how transmitted light can activate a chemical reaction.

• To create a product using the photochemical process.

• To appreciate the art of chemistry.


• Molecular energy

• Technical applications




Purpose

After completing this activity you will be able to explain how transmitted light can activate achemical reaction.

Industrial Applications

The cyanotype process is an inexpensive non-silver photographic procedure. You can viewcyanotype prints by accessing this website:

http://www.mikeware.demon.co.uk/cyanotypes.html (last access in July 1998)

Blueprint paper is a commercial application of this process.

Introduction

Radiant energy can produce chemical reactions and photochemistry is the study of howmatter stimulated by light can undergo chemical change. During a photochemical reaction achemical species absorbs light and enters into an excited state. Species in excited statesgenerally have different electron distributions than they do in the ground state and can acceptand donate electrons more readily.

singletgroundstate

ionizedspecies

singletexcitedstate

Figure 1.

Excited states species have lower ionization energies and are better electron donors thanground states.



singletgroundstate

anion singletexcitedstate

Figure 2.

Excited states have larger electron affinities and are better electron acceptors than ground states.

To prepare the photographic paper for the cyanotype process, separate solutions of iron(III)ammonium citrate and potassium ferricyanide are prepared. Equal amounts of solutions aremixed and the paper is coated with the mixture and allowed to dry. When the dried paper isexposed to ultraviolet light, the iron(III) ions in the iron(III) ammonium citrate is reduced toiron(II) by the citrate ions. The iron(II) ion then quickly reacts with the ferricyanide ion toform the insoluble iron(III)ferrocyanide.

Fe + e h

Fe

Fe + Fe(CN) Fe Fe(CN)

3(aq)

2(aq)

2(aq) 6

3-(aq) 4 6 3(s)

+ +

+

− →

→ [ ]

υ

Safety, Handling, and Disposal

Wear gloves and safety goggles and work in a well ventilated room. Solutions of ammoniumiron(III) citrate and potassium ferricyanide can be stored in brown bottles for up to one year.Do not add heat or acid to potassium ferricyanide and keep away from sources ofstrong ultraviolet light. Poisonous hydrogen cyanide gas may be produced. Followdisposal procedure #26a for excess ammonium iron(III) citrate and disposal procedure #14for excess potassium ferricyanide from the current Flinn Chemical Catalog.

Materials Needed

ammonium iron(III) citrate solutionpotassium ferricyanide solution100-mL beaker2 sheets watercolor paper1-inch foam brush

Procedure

Day 11. Pour 25 mL of each solution into a beaker.2. Obtain two pieces of watercolor paper and a foam brush.3. Brush an even coating of the mixture onto the paper. Work in a dim light.4. Let the paper air dry in the dark.



Day 1 HomeworkFor homework you will make the negative needed for Day 2 assignment. Your teacher will giveyou a blank acetate transparency. Use a permanent marker to create an imitation black-and-whitenegative. Draw a design or picture on the transparency. Varying the shading in the negative willgive a variety of color intensities. This negative will be placed on the photo developing paperwhile it is being exposed to the sunlight.

Day 21. Cut one of your coated papers into quarters.2. Place one quarter in total darkness, the second quarter under a red light, the third quarter

under a green light, and the fourth quarter in sunlight. Expose for about 15 minutes.3. With the second piece of coated paper you will make a photogram. Take the negative you

designed and place it on top of your paper. Expose your paper to bright sunlight for abouthalf an hour.

4. When your exposure appears dark enough, wash your print in running water until all of theyellow stains disappear.

5. Dry your print.

Questions

1. Fe + Fe(CN) Fe Fe(CN)63-

4 6(aq) 3(s)2+ → [ ]( )aq

What is the oxidation number of iron in Fe(CN)63-?

What is the oxidation number of each iron in Fe4[Fe(CN)

6]

3?

2. The iron(III) ion in ammonium iron(III) citrate is light sensitive. When ammonium iron(III)citrate is exposed to light, this reaction occurs:

Fe e h

Fe3(aq)

2(aq)

+ ++ − →υ

What color of light activates this reaction?

What wavelength is associated with this light?

Approximately how much energy is associated with this reaction?

3. How might this reaction be similar to the production of photochemical smog?

References

These websites were last accessed in July 1998:

http://www.lightfactory.org/text/cyanotype2.html

http://duke.usask.ca/~holtsg/photo/cyanotone.html

http://www.bostick-sullivan.com/c_cyano.htm




Instructor Notes

Time Required

Day 1 - 15 minutes to coat paperDay 2 - 10 minutes to set papers under different colored lights and in the sun.

After 30 minutes exposure to light, it will take about 15 minutes to wash the photogram and makecomparisons of exposure to different colors of light.

Group Size

Students can work individually for this activity.

Safety, Handling, and Disposal

Wear gloves and safety goggles and work in a well ventilated room when working withchemicals. Solutions of ammonium iron(III) citrate and potassium ferricyanide can be storedin brown bottles for up to one year. Do not add heat or acid to potassium ferricyanide andkeep away from sources of strong ultraviolet light. Poisonous hydrogen cyanide gas may beproduced. From the Flinn Chemical and Biological Catalog Reference Manual, followdisposal procedure #26a for excess ammonium iron(III) citrate and disposal procedure #14for excess potassium ferricyanide.

Points to Cover in the Pre-Lab Discussion

Pre-Lab Demonstration

See A Photochemical Reaction

Some Additional Information on Photochemistry

The diagram below looks at the energy differences between a photochemical reaction and athermal reaction. Photochemical reactions can be designed to select which chemical speciesabsorb light and enter into an excited state and so they can be better controlled than thermalreactions.

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