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MCAT Organic Question — Isobutyric Acid

In order to extract isobutyric acid from a solution of diethly ether, one should wash the solution with:

 

a) 1 30mL wash of water

b) 3 10mL washes of water

c) 1 30mL wash of hexane

d) 3 10mL washes of hexane

 

Explanation

 

Isobutyric acid has a carboxylic acid group, is polar, and can readily hydrogen bond. It can be extracted from the organic solvent, diethly ether, by washing with water. Multiple smaller volume washer extract better than one large volume wash. Use of a second organic solvent, hexane, will not extract the isobutyric acid from the diethyl ether.

 

a) 1 30mL wash of water, incorrect, Multiple smaller volume washes will yield higher extraction results.

b) 3 10mL washes of water, correct, Isobutyric acid will enter the aqueous layer and wash off of the organic layer of diethyl ether.

c) 1 30mL wash of hexane, incorrect, Hexane is another organic solvent like diethyl ether.

d) 3 10mL washes of hexane, incorrect, See c).

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