Question

Why do we do extractions three times and not only once? Refer to Calculation (1) on the prelab? ​

Answer 1

answer:

When a solution is placed in a separatory funnel and shaken with an immiscible solvent, solutes often dissolve in part into both layers. The components are said to "partition" between the two layers, or "distribute themselves" between the two layers. When equilibrium has established, the ratio of concentration of solute in each layer is constant for each system, and this can be represented by a value K (called the partition coefficient or distribution coefficient).

K=Molarity in organic phaseMolarity in aqueous phase(4.5.1)

For example, morphine has a partition coefficient of roughly 6 in ethyl acetate and water. 2 If dark circles represent morphine molecules, 1.00g of morphine would distribute itself as shown in Figure 4.11.

Diagram of morphine beside diagram of separation. Image A: 50mL ethyl acetate above 50mL water in flask, black dots (representing morphine) dissolved in both. Below, equation reads K = [morphine]ethyl acetate / [morphine]water = 0.0600M / 0.0101M = 5.95. B: 25mL ethyl acetate over 50mL water in flask, black dots in both. Below, equation reads K = 0.105M/0.0177M = 5.93.

Figure 4.11: Distribution of morphine in ethyl acetate and water.

Note that with equal volumes of organic and aqueous phases, the partition coefficient represents the ratio of particles in each layer (Figure 4.11a). When using equal volumes, a K of ∼6 means there will be six times as many morphine molecules in the organic layer as there are in the water layer. The particulate ratio is not as simple when the layer volumes are different, but the ratio of concentrations always equals the K (Figure 4.11b).

The partition coefficients reflect the solubility of a compound in the organic and aqueous layers, and so is dependent on the solvent system used. For example, morphine has a K of roughly 2 in petroleum ether and water, and a K of roughly 0.33 in diethyl ether and water. 2 When the K is less than one, it means the compound partitions into the aqueous layer more than the organic layer.

explanation:

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