Lab Report Partition Coefficient

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Chem 322 Friday
Partition Coefficient (Extraction) Lab for Benzoic Acid
Reaction Mechanism:

The purpose of this particular lab was to demonstrate the difference in separation of Benzoic acid in water and Dichloromethane. Also the difference in separation of Benzoic acid in bicarbonate and Dichloromethane. By calculating the partition coefficient for each of these separations, it became clear the differences in the separation of the aqueous and organic layers. Observations & Results:

In each of these separations, when the layer were mixed together and allowed to settle, two distinct layers were formed. The aqueous layer was on top and the organic layer was on the bottom. In both cases, gaseous pressure was built up in the separatory funnel but in the bicarbonate separation, the gas build up was much greater due to the reaction giving off carbon dioxide. When each product was weighed, a white crystalized structure had formed in the erlenmeyer flask. Calculations:

Partition Coefficient for Water
K = .36g organic layer / .04 grams water layer
K = 9.0

Partition Coefficient for Bicarbonate
K = .02g organic layer / .40g bicarbonate layer
K = .05
From this lab, we have learned that the partition coefficient for benzoic acid can differ greatly depending on what the aqueous layer in the separation is. For example, Benzoic acid is soluble in dichloromethane while only slightly soluble in water which leads to a large K value. In the other experiment, the benzoic acid reacts with the bicarbonate to form a salt and carbon dioxide. This reaction keeps the product mostly in the bicarbonate layer, therefore leading to a small K value. These K value for each separation make sense, because a high K value means that the majority was in the organic layer while a low K value means the majority was in the aqueous layer.
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