Compare the pKa of acetic acid in water, carbon tetrachloride, and dimethyl sulfoxide (these are all solvents).

Answer 1

The greater the polarity of the solvent, the greater is the Ka of acetic acid. Solvents of greater polarity enhance the ionization of acetic acid. The pKa is defined as - log Ka; therefore, the greater the Ka, the lower the pKa (e.g. a Ka of 0.1 has a pKa of 1, but a Ka of 0.0001 has a pKa of 4).

The order of polarities for the solvents in question are H2O > (CH3)2SO > CCl4; therefore, the order of pKa for acetic acid in each solvent would be pKa _CCl4 > pKa _(CH3)2SO > pKa _H2O.