Home > Chemistry > Chemistry 1A Part Deux: Lecture 20 Notes

Chemistry 1A Part Deux: Lecture 20 Notes

Overview

Business as usual.  This is 47 minute lecture on separating equilibrium.  They are having a test very soon.

Details

Equalibrium considerations can be used to design methods for separating components of mixtures.

The Case of Amnesic Shellfish Poisoning

One morning in the summer of 1981, hundreds of crazed birds attacked the city of Capitola, Ca.  The birds cried like babies as they dove into streetlamps, crashed thgough glass windows and attacked people on the ground.

In winter of 1987, over a hundred people became sick after eating blue mussels on PEI, Canada.  Some showed emotional volatility with uncontrolled crying or aggressiveness.

Strategy to isolate the toxin.  Treat poisoned and contaminated mussels.  Treat the residue with methanol to extract polar molecules.  Rates that eat the residue live, rats that eat the methanol die.  Evaporate the methanol.  Rats exposed to the vapor lived,  rats exposed to the residue died.  The residue had a higher boiling point.

Partitioning between two phases involves a seperatory funnel.  Liquids separate by density, say hexane on top, water on the bottom.

Solvent extraction partitions between two liquids.

A (water) = A (octanol)

K = [octanol]/[water]

Octanol likes membranes.

DDT/C14H9Cl5    960,000

Hexane C6H14  4500

Iodine I2 200

Ethanol CH3CH2OH 1

Acetic Acid CH3COOH .6

The number on the right refers to the proportion of the molecule found in octanol.

For solvent extraction, they used CH2H2 versus water.  The nonpolar mice live, the water mice died.  It is a big molecule, polar, in water.  Run the aqueous layer through a column.

This is chromatography, separation by partitioning between mobile phase and stationary.  Essential components include a column with a stationary phase, a detector, and a mobile phase of liquid or gas.

Column liquid chromatography involves different types of solute interactions with stationary phases.  Nonpolar stationary phase/Anion exchange polymer resin/Biological affinity stationary phase/Molecular size exclusion gel.

K = [stationary phase]/[mobile phase]

As soon as you inject reagent into a column, they begin to partition.  If k is small, it goes through the column first.

Ion exchange chromotography partitions between liquid and resin.  Chromotographic olumn is filled with a slurry of ion exchange resin.  This is a cross linked polymer with ions.

Co(H2O)2+(pink) + 4Cl- = CoCl4-2(blue) + 6H2O    K = 2.5*10^-4

Cu(H2O)2+(green) + 4Cl- = CuCl4-2(yellow) + 6H2O    K = 200

In 3 M HCl solution, cobalt exists as Co(H2O)6+2 and copper exists as CuCl4-2.

More cobalt is pink, more copper is yellow.  Therefore, in a positive column, copper will bind more and will move down more slowly.

Partitioning of a solute into a nonpolar stationary phase followed by its pH change induced elution.  HA + OH – = H2O + A-.  The base comes down, H+ comes off, A- is left.

High voltage electrophoresis separates molecules by charge.

So back to the mouse experiment, they ran acid/base through the column and only when the base was eluded did the mouse die.  Then they ran high voltage electrophoresis and one mouse died.  Mass spec was used to identify the molecule then.

Domoic acid was identified.  It mimics glutamate, binding to nerve cell receptors.  The case of the poison shellfish was solved.

Review

PV = nRT

Chromatography: stationary, mobile, detector.

G= H – TS

IGL: Point source, random motion, elastic collisions, high temperatures, low pressures

s 2, p 6, d 10, f 14

(P + n^2/a^2) (V -nb) = nRT  van der Waals gas

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