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Welcome back to R-C Labs : 

Welcome back to R-C Labs Experiment 4, Part 2 February 7, 2008 C343 Spring 2008

Objectives for Experiment 4.2: 

Objectives for Experiment 4.2 Determine purity of recrystallized compounds from previous week Mixture, acid compound, neutral compound Compare acid and neutral to real analgesics using Thin Layer Chromatography (TLC) Confirm presence of acid and neutral compound by IR spectroscopy Determine if F.N.P. can use the unknown you analyzed as a generic substitute

Purity Determination: Melting Point: 

Purity Determination: Melting Point Melting point range: the range of temperatures over which a a crystal first begins to melt until it is completely liquid Melting point depends upon how tightly a crystal packs No impurities = ____________ Impurities Present = ______________.

Purity Determination: Melting Point: 

Purity Determination: Melting Point Impurities _______ “true” melting point Impurities cause a crystal to pack loosely _________________ m.p. because ______ is required to overcome the intermolecular forces that make the crystal a solid To determine a melting point Perform the test at least twice Obtain m.p.’s that are within 1-2oC of each other

Separation Techniques: 

Separation Techniques Types: Distillation – separates by differences in b.p. Extraction – separate by differences in solubility Chromatography – ________________________ ________________________ Experiment 3 Thin Layer Chromatography (TLC) Separation and purity-determination technique Use to compare unknowns to No Doz, Bayer, and Tylenol

TLC Materials: 

TLC Materials Eluent: Liquid phase Chamber TLC Paper: Stationary Phase

TLC Theory: 

TLC Theory Stationary phase (TLC plate) TLC plate is coated with silica gel _____________ is main intermolecular force involved in a TLC separation Polar molecules “stick” to plate Non-polar molecules do not “stick” to plate

TLC Theory (cont’d): 

TLC Theory (cont’d) Liquid phase (called the eluent) Usually a “non-polar” organic solvent, is mixed with a little “polar” organic solvent

TLC Theory (cont’d): 

TLC Theory (cont’d) Separation of compounds occurs due to differences in partitioning between liquid and stationary phases Polar molecules will spend a greater amount of time “sticking” to the plate Acid component of mixture Non-polar molecules will spend a greater amount of time dissolved in the eluent Neutral component of mixture

TLC Theory (cont’d): 

TLC Theory (cont’d) Molecules with low affinity for the TLC plate Molecules with high affinity for the TLC plate

TLC Experiment: 

TLC Experiment First: Mark the origin Second: Apply sample Third: Place into chamber Eluent Origin

TLC Experiment: 

TLC Experiment Forth: Eluent ascends plate Direction Solvent Travels Fifth: Remove plate & label solvent front Front

Determine the Rf for Spots: 

Determine the Rf for Spots Origin Solvent Front Spots Rf = distance spot traveled distance solvent front traveled 2 cm 10 cm Rf = 2 cm 10 cm 0.2 Rule of thumb: polar compounds have low Rf values

Use of TLC for comparisons: 

Use of TLC for comparisons Determine purity and corroborate identity of sample Pure Sample Recrystallized Sample

For Successful TLC Experiment: 

For Successful TLC Experiment Do not apply too much sample to plate Streaking Disproportionately Large Spots