Question

4a. What is the predominant integer charge state of the following substances at pH = 7.40 ? Predominant charge state Substance Acetic acid, CH.COOH CCOOH Dimethyl amine Phosphoric acid, H,PO, Valine (an amino acid) Ethylenediamine EDTA PK (s) 4.76 10.77 2.15.7.20, 12.38 2.29.9.72 6.85.9.93 0.0.1.5, 2.00. 2.69.6.13, 10.37

Answer 1

4a. If pKa < pH, the corresponding proton will be released, and the conjugate base will be formed. If pKa > pH, the corresponding proton will not be released.

Acetic acid: pKa < pH; so, the charge state is -1

Dimethylamine: pKa > pH; so, the charge state is zero

Phosphoric acid: pKa < pH for two hydrogens (out of 3); so, the charge state is -2 (2 protons will be released)

Valine: pKa < pH for one hydrogen (out of 2); so, the charge state is -1

Ethylenediamine: pKa < pH for one hydrogen (out of 2); so, the charge state is -1

EDTA: pKa < pH for 5 hydrogens (out of 6); so, the charge state is -5 (5 protons will be released)