pH to control solvent extraction

Consider a compound such as:
CH₃-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-COOH
and focus on the carboxyl group:

At low pH where there is a high concentration of H⁺, the pressure is to keep the hydrogen from ionizing. This compound is thus dominated by the long hydrocarbon chain and is essentially non-polar despite some effect of the weakly acidic carboxyl group.

At high pH and low H⁺, ionization is favored. This leaves a charged group to dominate and makes the compound essentially polar. By switching from one pH range to another, the compound changes its polarity and its preference for residing in either a polar or non-polar solvent.

Test yourself 

created March 1997