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From MyMCAT

Liquid-liquid extraction, also known as solvent extraction, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. Acid-base extraction is the most common separation method and follows a procedure of sequential liquid-liquid extractions to purify acids and bases from mixtures based on their chemical properties. The final product is largely free of neutral and acidic or basic impurities. Unfortunately, it is not possible to separate chemically similar acids or bases using this simple method.

A student with an unknown mixture of organic molecules perform a series of liquid-liquid extractions to identify the compounds in their solution. The student initially sets up the experiment with the addition of 20 mL diethyl-ether and 3 grams of the unknown mixture in a separating funnel. The student then added 10 mL H₂0. After following the liquid-liquid extraction procedure involving gentle shaking and venting, the student extracted an aqueous solution, solution A. To identify the compound of solution A, the student added excess K₂Cr₂O₇ and used distillation to purify away the H₂0. IR analysis showed strong peaks at 3005cm^-1 (narrow), 1725cm^-1 (narrow), 1420cm^-1 (narrow), 1405cm^-1 (narrow), and 1200cm^-1 (narrow).

The student then proceeded with a second extraction using 10mL of HCl. This extraction yielded aqueous solution B. Slow addition of nitrous acid to solution B on ice showed no visible signs of a reaction however subsequent heating resulted in the rapid proliferation of N₂ gas suggesting their was a diazonium intermediate.

Following the acid extraction, the student turned to the use of 10mL of NaHCO₃. The student then extracted the aqueous layer which, following an acid workup, resulted in solution C.

The student repeated the base extraction step a second time, this time however, using NaOH. The removal of the aqueous extract, solution D, left behind an organic layer, solution E.

1) Solution A is most likely to contain? - propanoic acid - propane - 1-pronanol + 2-propanol