# CHEMISTRY

How can we determine the equivalence point ( or end point ) in the curves in titration ( strong acid/weak base and weak acid/strong base )

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1. Do you mean how to calculate the pH at the equivalence point or how they look? Here is how they look; i.e., its' the mid-point of the almost vertical part of the curve.

If how you calculate it you "hydrolyze" the acid or base salt; e.g., for weak acid/strong base such as HAc where HAc is acetic acid, you have
HAc + NaOH --> NaAc + H2O. So at the equivalence point you have ONLY NaAc and H2O so the pH is determined by the hydrolysis of the salt, in this case it is
.........Ac^- + HOH ==> HAc + OH^-
I........C...............0......0
C........-x..............x......x
E........C-x............x.......x
Then Kb for Ac^- = (Kw/Ka for HAc) = (x)(x)/(C-x). You will know the concn of Ac^- and Kw and Ka for HAc and you calculate x = OH^- and convert to pH. That gives you the pH at the equivalence point.

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