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The main areas of the titration curve for the reaction of 0.020 M H2SO3 with 0.1000 M NaOH are highlighted below. Keep in mind that this is an example of a weak acid titration and that the data for your assigned sample may look different. (What factors might change the shape of the titration curve? How do those factors change with the different concentrations and identities of the assigned samples?)
Note that H2SO3 is a diprotic acid, and the titration curve contains a second buffer region and a second equivalence point. The volume of NaOH added at the second equivalence point is approximately twice that of the first equivalence point.
Titration of 0.020 M H2SO3
Titration of 0.020 M H2SO3
At the initial point, the solution is just acid in water since no base has been added.
2. Before the first equivalence, a buffer exists – a mixture of the acid, H2SO3, and its conjugate base, HSO3–.
3. At the first equivalence point, H2SO3 has been converted entirely to HSO3–.
4. Between the first and second equivalence points, a buffer exists – a mixture of the acid, HSO3–, and its conjugate base, SO32–.
5. At the second equivalence point, HSO3– has been fully converted to SO32–.
6. After the equivalence point, the pH is dominated by the excess of strong base added.
Would these equations be the same or different for the other samples (H3PO4, HNO3, H2SO4, Na2CO3)?
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