# Chromo - Exam 3(1 The Scherrer equation Crystallite...

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Exam 3 (1) The Scherrer equation. Crystallite Diameter t = λ /Bcos Θ With B in radians and Θ in degrees. Width at ½ height in degrees = 31/2 – 26/2 = 2.5 degrees = 0.043 rads Peak appears at ~30 degrees 2 Θ or 15 degrees t = 0.15418 nm/0.043 rads cos 15 = 3.7 nm (2) A = -log T; with T as a fraction, not a %. (3) Be careful of deviations from Beer’s law for absorbances over ~0.5. (4) See Laporte selection rule and inversion symmetry in notes.

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Concept Te\$t What type electronic transition occurs in methanol? ( Α ) π π * (B) σ π * (C) n π * (D) n σ *
Concept Te\$t The more conjugation in a molecule the: ( Α ) Higher its extinction coefficient (C) More blue shifted its electronic absorbance (D) Lower its quantum yield of fluorescence (B) More red shifted its electronic absorbance

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Exam 3 (8) Phosphorescence is slow because of the change in spin. (9) With B as donor and C as acceptor there is good overlap between the donor emission and acceptor absorbance. (11) N 2 and O 2 do not have IR active vibrations so they cannot absorb and re- emit IR light. (5) Methanol does not have any π - π * transitions (it has an n σ *), so we wouldn’t expect an absorbance in the visible, just UV. The others have π - π *, and the more conjugation equals red shift in absorbance.
Chapter 26: Chromatography Homework: 26-1, 26-2, 26-6, 26-7, 26-8, 26-9, 26-11, 26-17, 26-19, 26-22 Chroma: Color Graphein: Writing First used to separate plant pigments. Solutions were passed through columns of calcium carbonate and different pigments appeared as separate bands of color. (Liquid Chromatography) Most chemical analyses would be impossible without a way to separate the analytes.

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EPA Method 601: Volatile Halogenated Hydrocarbons How are all of these compounds detected simultaneously?
Separations come in many forms and sizes. Conventional Separations Paper Separations Lab-On-A-Chip Diagnostics for All http://www.dfa.org/

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EPA Method 601 Water sample is purged with Ar for 10 min. to transfer halocarbons onto a carbon trap. Trap is heated rapidly to desorb halocarbons, which flow into a thin capillary column. Halocarbons are separated and then detected. The chromatogram below shows intensity vs. time. Many different molecules are detected in ~40 min.
How are all these molecules separated? What determines the peak resolution? What determines the time it takes to separate molecules?

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The Idea EtOH EtOH EtOH EtOH A drop of blood from a suspected drunk driver is placed in water. Which component would you expect to be found in the vapor phase above the water? (A) Blood cells (B) Proteins (D) Cholesterol (C) Ethanol Can you write a reaction and equilibrium constant for this process?
The Idea EtOH EtOH EtOH EtOH EtOH (aq) EtOH (g) K = P g /[EtOH] aq The concentration of alcohol in blood can be determined by measuring the ethanol partial pressure above the liquid as long as K is known.

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Chromo - Exam 3(1 The Scherrer equation Crystallite...

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