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.
So you expect that Benzene, as it has a lower K, and therefore a higher concentration in the aqeous phase, to be more efficient?
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.
The equation as I recall is,
q^n = (Vaq/Vaq+K*Vorg)^n,
where n =number of extractions.
You didn't define enough for me. Here is what I have where fn is the fraction left of the solute REMAINING in the water layer after n extractions.
fn = [1+K*(Vo/Va)]-n
Of course, you can calculate it three times from a single extract, too.
a) In order to determine which organic solvent is expected to extract the acid most efficiently from water, we need to consider the distribution coefficient (D) for each solvent. The distribution coefficient is a measure of how much more the acid prefers to be in the organic solvent compared to water.
For butanoic acid (pKa = 4.8), the higher the distribution coefficient (D), the more efficiently the acid will be extracted into the organic solvent.
Comparing the distribution coefficients of benzene (D = 3.0) and octanol (D = 6.2), we see that octanol has a higher D value. This indicates that octanol is the more efficient solvent for extracting butanoic acid from water.
So the answer to part (a) is that octanol is expected to extract the acid most efficiently from water.
b) To determine whether one extraction with 300 mL or three extractions with 100 mL each is more effective when extracting butanoic acid into benzene, we can use the equation you provided:
q^n = (Vaq/Vaq + K*Vorg)^n
In this equation, q is the fraction of acid extracted, n is the number of extractions, Vaq is the volume of water, Vorg is the volume of organic solvent, and K is the distribution coefficient for butanoic acid between water and benzene.
Let's calculate the fraction of acid extracted for each scenario:
For one extraction with 300 mL:
q = (300 mL / (300 mL + (3.0 * 300 mL)))^1
q = (300 mL / (900 mL)) = 1/3
For three extractions with 100 mL each:
q = (100 mL / (100 mL + (3.0 * 100 mL)))^3
q = (100 mL / (400 mL))^3 = 1/64
Comparing the fractions of acid extracted, we see that one extraction with 300 mL is more effective than three extractions with 100 mL each. The fraction of acid extracted is 1/3 for one extraction, while it is only 1/64 for three extractions.
So the answer to part (b) is that it is more effective to perform one extraction with 300 mL when extracting butanoic acid into benzene.