Biochemistry 2280A Lecture Notes - Lecture 3: Mast Cell, Acid Dissociation Constant, Histidine

• School: Western University
• Department: Biochemistry
• Course: Biochemistry 2280A
• Professor: Chris Brandl

Document Summary

Problem: a 0. 1m solution of a generic weak acid (ha) has a ph of 2. Determine the pka: write balanced equation, ha h+ + a, write equilibrium expression, ka = [h+] [a-] / [ha, use the ph to calculate [h+, ph = -log[h+] [h+] = 0. 01m: substitute values into equilibrium expression to yield ka. [a-] = [h+] = 0. 01 m: ka = 0. 01*0. 01 / 0. 1 = 0. 001 m, calculate pka, pka = -log(ka) = 3. At a given ph: calculate extent of ionization of a group. From this, calculate the net charge on this group. Relationship between ph, pka, ionization state: when ph < pka, majority of group is protonated, when ph > pka, majority of group is deprotonated. The henderson-hasselbalch equation: ph = pka + log ([a-]/[ha]) Case 2: ph = 1 (< pka: ph = pka + log ([a-]/[ha], 1 = 2 + log ([a-]/[ha], 10-1 = [a-]/[ha, 0. 1 = [a-]/[ha]