Page 1 of 1

pH Curve at Equilibrium

Posted: Fri Dec 04, 2015 2:22 pm
by Alex Nguyen 3I
Where on the pH curve is the solution at equilibrium? Is it when the curve levels out? Why is the halfway point to the stoichiometric point where pH=pKa? Also, can someone explain again why when the concentrations of the weak acid and conjugate base are the same, it is an optimum buffer?

Re: pH Curve at Equilibrium

Posted: Fri Dec 04, 2015 4:22 pm
by Chem_Mod
The solution is at equilibrium at all points on the curve. The x-axis represents amount of titrant, and the y-axis represents the equilibrium pH of a solution that had x amount of titrant added.

The best buffer is one that has an equal amount of HA and A- because it will be able to resist changes in both directions (adding strong base OR strong acid). This can be visualized on the titration curve as the flat-region at the HALF-equivalence point. Note that as you move along the x axis, the y-value stays nearly constant.