exp3w08

exp3w08 - Experiment 3: Acid, Base, Neutral Separation...

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Experiment 3: Acid, Base, Neutral Separation (Liquid- Liquid Extraction, Drying, recrystallization) Mohrig, Chapter 8- 9 This experiment is designed to 1) demonstrate that immiscible solvents, such as water and ether, form separate layers on the basis of density (top = lighter, bottom = heavier), 2) demonstrate extraction of a solute (liquid or solid) from one solvent to another on the basis of its partition coefficient, 3) employ pK a ’s and acid or base to change the par- tition coefficient of an acidic or basic substrate, 4) introduce the concept of using a flow- chart to rapidly summarize a laboratory procedure, and 5) demonstrate how a drying agent removes traces of water from non-aqueous solutions, thereby drying the com- pound dissolved in the organic (non-aqueous) layer. Discussion : One central method for purification of an organic solid or liquid is a process called extraction. Liquid-liquid extractions take advantage of the difference in solubility of a substance in two immiscible liquids. The two immiscible liquids used in an extraction process are called the solvent , and the extracting solvent . The two immiscible liquids are separated using a separatory funnel or a test tube. The flow chart for the extraction experiment: CO 2 H O NH 2 CO 2 Et dissolved in Et 2 O 16 mL shake with 3M HCl (8 mL) NH 3 + Cl CO 2 Et aqueous organic shake with 3M HCl (8mL) NH 3 + Cl CO 2 Et aqueous organic CO 2 H O shake with 3M NaOH (8 mL) CO 2 Na + aqueous organic CO 2 Na + aqueous organic O chill add 6M HCl (9mL) ppt and filter wash ppt with DI (4mL) aqueous (NaCl) organic get m.p CO 2 H chill add 6M NaOH (9mL) ppt and filter wash ppt with DI (4mL) aqueous (NaCl) organic get m.p. NH 2 CO 2 Et 500 mg of a 1:1:1 wt% mixture acid neutral base wash with Et 2 O aqueous (NaCl) shake with 3M NaOH (8 mL) wash with Et 2 O evap evap wash with brine (4mLX2) aqueous (NaCl) dry over Na 2 SO 4 , filter and evap organic get m.p. C7H6O2 Mol. Wt.: 122.12 C13H8O Mol. Wt.: 180.2 C9H11NO2 Mol. Wt.: 165.19 10 Quiz ideas (3) Write the balanced equation for the aniline + HCl gas. Where will the equilibrium lie? By how much? What about benzoic acid and triethylamine? If a mixture of benzoic acid and triethyl amine were suspended in a mixture of water and methylene chlo- ride, what would be in the aqueous layer? What is the purpose of the brine wash? What would Raoult say about azetropes? Define the following stationary phase, mobile phase, elution, eluent, normal phase, reverse phase. List several common adsorbents for chromatography. Write the equilibrium expression for the adsorption process observed on a TLC plate. List several precautions for spotting a TLC plate.
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This note was uploaded on 04/07/2008 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

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exp3w08 - Experiment 3: Acid, Base, Neutral Separation...

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