Two students are separating a BHA-BHT mixture, each one beginning with 3 mL of p
ID: 1087802 • Letter: T
Question
Two students are separating a BHA-BHT mixture, each one beginning with 3 mL of petroleum ether, followed by 6 mL of acetone-petroleum ether compound mobile phase, and ending with 3 mL of acetone. The student employing 1:1 mixture starts adding it to the column reservoir when 1.5 mL of straight petroleum ether remains, and then begins adding straight acetone when 1.5 mL of mixture remains. In contrast, the student employing 1:3 mixture starts adding it to the column reservoir when 1.0 mL of straight petroleum ether remains, and then begins adding straight acetone when 2.0 mL of mixture remains. Explain the rationale underlying the two mixing patterns.
Explanation / Answer
The separation of BHA-BHT mixture depend on type of molecule and their polarity. The mixture could form an azeotrope when different proportions are used. As in this case one uses 1:1 and another 1:3.
The difference in the petroleum ether remaining and the addition of acetone could be attributed to azeotrope formation with the molecules in petroleum,ether and acetone. As the composition used the mixture is different, it could lead to formation of inseparable compounds of BHA-BHT. In order to break the azeotrope, the students are adding acetone in different volumetric proportions.
The seperation of azeotropic mixture depends also on the temperature. But there is no information about the temperature.
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