The distribution co-efficient of butanoic acid (pKa = 4.8) between water and two organic solvents are given below;
Benzene D= 3.0
Octanol D= 6.2
a) which organic solvent is expected to extract the acid most efficiently from the water? explain your answer.
I understand that D is a measure of extraction efficiency but I am having trouble answering this question.
b) When extracting butanoic acid into benzene is it more effective to do one extraction with 300mL or three 100mL extractions? Support your answer with calculations.
Distribution coefficients = Ko/a so large K values occur as the result of higher solubility in the organic phase than in the aqueous phase. In contrast, lower K values result from a higher concentration in the aqueous phase than in the organic phase. Therefore, ......can you take it from here?
B. You can go through the calculation (with a made up problem if necessary) to see how this works, but in general three extractions ALWAYS does a better job than a single extraction of the same volume; i.e., three 100 mL extractions do a better job than a single 300 mL extraction. Post your work if get stuck on the calculation or on the formula.
a) The distribution coefficient (D) is a measure of how efficiently a solute is extracted or distributed between two immiscible phases, in this case, water and the organic solvents. A higher D value indicates a greater extraction efficiency.
Comparing the D values of benzene (D = 3.0) and octanol (D = 6.2), we can see that octanol has a higher value. Therefore, octanol is expected to extract the butanoic acid more efficiently from water compared to benzene.
b) To determine whether it is more effective to perform one extraction with 300 mL or three extractions with 100 mL each, we need to consider the total amount of solute extracted.
Let's assume the initial concentration of butanoic acid in water is C (in mol/L). When performing one extraction with 300 mL, the amount of butanoic acid extracted can be calculated as follows:
Amount extracted in one extraction = C * 300 mL
When performing three extractions with 100 mL each, the amount of butanoic acid extracted in each extraction is:
Amount extracted in each extraction = C * 100 mL
In three extractions, the total amount extracted will be three times the amount extracted in each extraction:
Total amount extracted in three extractions = 3 * (C * 100 mL)
We can compare these two quantities to determine which method is more effective.
If we assume the extraction efficiency is the same for both methods, we can conclude that one extraction with 300 mL is more effective when:
C * 300 mL > 3 * (C * 100 mL)
Simplifying,
300 > 3 * 100
300 > 300
Since the inequality is not true, it means that performing three extractions with 100 mL each is more effective in extracting the butanoic acid from water compared to a single extraction with 300 mL.