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lecture4topost - A = b c Absorbance vs Wavelength 1 0.9 0.8...

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Spectrophotometry Spectrophotometry & Beer’s Law N N O O SO 3 - - SO 3 H H A = ε b c Absorbance vs Wavelength 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 350 380 410 440 470 500 530 560 590 620 650 680 710 740 Wavelength (nm) Absorbance Absorbance vs Concentration Red Dye #2 at 470 nm 0 0.2 0.4 0.6 0.8 1 1.2 0 5 10 15 20 25 30 35 40 45 50 Concentration (mg/L) of F of F o o o o d d D D y y e e s s
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NO ADMITTANCE TO NO ADMITTANCE TO THE LAB WITHOUT THE LAB WITHOUT SAFETY GOGGLES SAFETY GOGGLES Gorilla 5 point penalty
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How is the absorption/transmission of light measured? How is the intensity of color related to the concentration of colored solutions? What is the quantitative basis for the color of substances? ? QUESTIONS ? What considerations go into the graphing of experimental data? Questions
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Concepts: Concentration Transmittance Absorbance Analytical Wavelength Beer’s Law Blank Electromagnetic Spectrum Absorptivity Techniques: Quantitative dilution Visible Spectroscopy Graphing Curve fitting Slopes Apparatus: Spectronic 20 Pipet Syringe Purpose Purpose
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For a simple, transparent, C O L O R E D material, e.g. Can plot a graph showing the of light of each discrete C O L O R that is transmitted by the solution BACKGROUND Transmitted light PURPLE CLEAR Incident white light I t I i I t 100 X %T = R O Y G B V R OYG B V Percent Transmittance
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T ra n s m it t a n c e o f W h it e L igh t b y a V io le t S o lu t io n 0 10 20 30 40 50 60 70 80 90 100 WAVELENGTH (nm) % TRANSMITTED Violet Red Or, instead, we can plot the percent of light absorbed Green Yellow Blue % Transmitted % Transmittance of White Light by a Violet Solution
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A b s o rb a n c e o f W h it e L ig h t b y V io le t S o lu t io n 0 10 20 30 40 50 60 70 80 90 100 W A V E L E N G T H ( n m ) Violet Red Blue Green % Absorbed Yellow % Absorbed of White Light by a Violet Solution
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VISIBLE AND ULTRAVIOLET : Electronic structure of molecules INFRARED REGION : Vibrations of molecules What determines the WAVELENGTHS of light that substances absorb? What determines INTENSITY of absorption? EFFICIENCY of INTERACTION between MOLECULES and ELECTROMAGNETIC RADIATION 100 nm – 800 nm 800 nm – 100 μ m
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Which DEVICE measures this phenomenon? A SPECTROPHOTOMETER measures the RELATIVE ABSORPTION of light of DIFFERENT WAVELENGTHS by a substance SOURCE MONO- CHROMATOR DETECTOR SAMPLE 37.7 SLIT DETECTOR to measure intensity of light transmitted through the sample, and ELECTRONICS to translate detector output into numbers SOURCE of light, MONOCHROMATOR an element to select particular wavelengths SAMPLE CONTAINER
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Detector output depends on intensity, wavelength & instrumental factors.
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This note was uploaded on 09/21/2009 for the course CHE 143 taught by Professor Raleigh during the Fall '09 term at SUNY Stony Brook.

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lecture4topost - A = b c Absorbance vs Wavelength 1 0.9 0.8...

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