8. Liquid-liquid extraction. A progressive (thought) exercise. a) Benzoic acid, C 6 H 5 CO 2 H, is insoluble in water (< 1 w/w %). A suspension of solid benzoic acid in water is treated with enough 1.0 M NaOH (aq) to react with the acid. What balanced acid-base reaction takes place? b) Judging by the products in this reaction, do you expect the benzoic acid to dissolve in the resulting aqueous phase? yes, or no, and why. c) Now, make a biphasic mixture of diethyl ether and water (see #7, above). Use a separatory funnel, as in the illustration above. Which substance is the upper layer? ______________
8. Liquid-liquid extraction. A progressive (thought) exercise.
a) Benzoic acid, C 6 H 5 CO 2 H, is insoluble in water (< 1 w/w %). A suspension of solid benzoic acid in water is treated with enough 1.0 M NaOH (aq) to react with the acid. What balanced acid-base reaction takes place?
b) Judging by the products in this reaction, do you expect the benzoic acid to dissolve in the resulting aqueous phase? yes, or no, and why.
c) Now, make a biphasic mixture of diethyl ether and water (see #7, above). Use a separatory funnel, as in the illustration above. Which substance is the upper layer? ______________
d) Add solid benzoic acid to these layered solvents, and mix thoroughly. Does the benzoic acid dissolve, and if so, where should it be found? ____________________
e) Then, make the pH of the aqueous phase alkaline (basic) with NaOH until the pH = 11.00. Again, mix thoroughly. Where should the benzoic acid be found now? ____________________
f) Separate the two phases carefully, placing them in separate beakers. Label them: ether phase; aqueous
phase. To the aqueous phase, carefully add HCl(aq) until pH = 2.00. What happens? Write the
balanced acid-base reaction that takes place.
g) How may solid benzoic acid (precipitate) be separated from the acidic aqueous solution? (method or technique)
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