pH Curve at Equilibrium

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Alex Nguyen 3I
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pH Curve at Equilibrium

Postby Alex Nguyen 3I » Fri Dec 04, 2015 2:22 pm

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?

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Re: pH Curve at Equilibrium

Postby Chem_Mod » Fri Dec 04, 2015 4:22 pm

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.

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