Solvent Extraction

What is partitioning?

What is the equation for the partition coefficient/distribution coefficient?

[Sorg] = organic solvent conc

[Saq] = aqueous solvent conc

What is the relationship between solubility and KD?

KD > 1

• more soluble in organic

KD = 1

• equally soluble in both

KD < 1

• more soluble in aqueous

Why is it more efficient to do multiple extractions at smaller volumes?

Continuously halves the concentration of the aqueous solvent, more solute is removed

What is extraction efficiency?

f(aq) = fraction of aqueous solvent left behind

How would partitioning work for weak acids?

DISSOLVE IN ORG = protonate w/ acid (HCl)

DISSOLVE IN AQ = deprotonate w/ base (NaOH)

*NOTE: ionised species MORE soluble in aq than non-ionised

How is the distribution ratio calculated for weak acids?

How would partitioning work for weak bases?

DISSOLVE IN ORG = deprotonate w/ base (NaOH)

DISSOLVE IN AQ = protonate w/ acid (HCl)

How is the distribution ratio calculated for weak bases?

What are the two different extraction efficiency equations (faq) used when dealing with easily ionisable and not easily ionisable substances?

KD = pH independent

• compounds NOT easily ionsed

D = pH dependent

• compounds EASILY ionised