Today: Exp.9, “Separation and Identification of an Unknown Mixture” (3 lab periods) “Qualitative analysis” This experiment includes: liquid/liquid extraction, IR, recrystallization, melting points, and other techniques you learnt this semester
Your unknown mixture (note its number!) contains: a carboxylic acid, a base (aromatic amine), and a neutral organic compound
determined by their melting points Carboxylic acids determined by their melting points Melting point ranges …
Bases: Aromatic Amines .. .. .. .. .. .. You will prepare a solid derivative and determine its melting point to identify your amine. What are desirable properties of a derivative?
determined by their IR What are we looking for in an IR? Neutral Compounds determined by their IR What are we looking for in an IR?
Liquid-Liquid Extraction Partitioning between aqueous and ether layer Which one is the ether layer?
Partition or Distribution Coefficient kp Refer to pp. 58 – 60 in your lab text and to today’s class handout solubility of compound A in solvent 2 solubility of compound A in solvent 1 or kp = (g/ml) organic layer / (g/ml) aqu. layer Kp = Question to think about…: Assume that 100 ml of an aqueous solution of compound A is extracted twice with 100 ml of ether (using fresh ether each time). If instead we extracted just once, but with a volume of 200 ml of ether, would we extract the same amount of A ? (Study handout!)
Separation Scheme
Begin of Separation
Isolation of Carboxylic Acid Do today
Separation of Neutral Do today
Separation of Amine
Amine Derivative: Prepare only Benzanilide 2b) Warning! Benzoyl chloride is an irritating liquid with a sharp pungent odor. Exothermic reaction with water. Wear safety glasses, gloves, use hood! Benzanilide m.p. 163 C
IR Spectroscopy Next Lab Lecture: IR Your IR samples must be ready for analysis today. Label the 50-mL E-flask with your sample with your name and section. Place a clean disposable glass pipette with a rubber bulb in this flask. IR spectra will be ready next time Next Lab Lecture: IR