Approximately 1.0 g of caffeine will dissolve in 28 mL of methylene chloride and

Question

Approximately 1.0 g of caffeine will dissolve in 28 mL of methylene chloride and in 46 mL of water. Calculate the distribution coefficient of caffeine in this solvent system. What are four characteristics of a good extraction solvent? If too much drying agent is added to a solution, what can be done to correct the situation? Identify the conjugate acid/conjugate base pairs for the structures above. Determine whether each of the five compounds is predominantly ionically or cova- lently bonded. Based upon this answer, indicate whether the compound would be expected to be more soluble in water or more soluble in methylene chloride.

Explanation / Answer

1) distribution coefficient is the ratio of concentration of a compound in two immiscible phases.

ie

Kd = solubility in organic solvent (g/mL) / solubility in water (g/mL)

Kd = (1.0g/28mL methylene chloride) / (1.0g/46 mL water)

Kd= (0.035g/mL methylene chloride) / (0.0217 g/mL water)

Kd = 1.612

2) characteristics of a good extraction solvent :

a) it should dissolve the extracted compound

b) it should be volatile

c) non toxic non flammable

d) it should be immiscible with the solution.

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