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Acids and Bases - Titration Curves

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Weak Acids and Strong Bases - Titration Curves
Weak Acid Titration Curve

Weak Acid Titration Curve

Todd Helmenstine
A weak acid only partially dissociates from its salt. The pH will rise normally at first, but as it reaches a zone where the solution seems to be buffered, the slope levels out. After this zone, the pH rises sharply through its equivalence point and levels out again like the strong acid/strong base reaction.

There are two main points to notice about this curve.

The first is the half-equivalence point. This point occurs halfway through a buffered region where the pH barely changes for a lot of base added. The half-equivalence point is when just enough base is added for half of the acid to be converted to the conjugate base. When this happens, the concentration of H+ ions equals the Ka value of the acid. Take this one step further, pH = pKa.

The second point is the higher equivalence point. Once the acid has been neutralized, notice the point is above pH=7. When a weak acid is neutralized, the solution that remains is basic because of the acid's conjugate base remains in solution.

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