Benzoic acid and quinine are dissolved in a solution of dichloromethane. Besides the normal neutral forms for benzoic acid and quinine, will there be any other chemical form(s) present in the dichloromethane solution? (benzoic acid pKa = 4.2; quinine pKa = 8.5)
Yes.
To determine the chemical forms of benzoic acid and quinine dissolved in a solution of dichloromethane, we need to consider their acid-base properties and the pKa values provided.
Benzoic acid (C6H5COOH) is a weak acid with a pKa of 4.2. In an aqueous solution, it exists primarily in its neutral form (C6H5COOH) and its conjugate base form (C6H5COO-). However, in a non-aqueous solvent like dichloromethane (CH2Cl2), it generally remains in its neutral form.
Quinine (C20H24N2O2) is a weak base with a pKa of 8.5. In water, it exists mainly in its neutral form (C20H24N2O2) and its conjugate acid form (C20H26N2O2+). Similarly, in a non-aqueous solvent like dichloromethane, it primarily remains in its neutral form.
Therefore, in a dichloromethane solution, besides the normal neutral forms of benzoic acid and quinine, there will not be any other major chemical forms present. Both compounds will exist predominantly as their neutral molecular species.