Titrations of Diprotic and Polyprotic Acids Video Lessons

Concept

# Problem: Phosphorous acid, H3PO4(aq), is a diprotic oxyacid that is an important compound in industry and agriculture.pKa1 = 1.30pKa2 = 6.70Calculate the pH for each of the following points in the titration of 50.0 mL of a 1.5 M H3PO3(aq) with 1.5 M KOH(aq).Part E. after addition of 100.0 mL of KOH

###### FREE Expert Solution

Calculate the volume needed to reach the equivalence point:

VB = 50.0 mL

To reach the 2nd equivalence point, we will need another 50.00 mL or a total of 100 mL of the base. Therefore, we reached the 2nd equivalence point.

After the first equivalence point, we will have H2PO3-. Write the chemical equation for the reaction between H2PO3- and NaOH.

Reaction:

H2PO3-(aq) + NaOH(aq) ⇌  HPO32-(aq) + H2O(l)
*Main group metals should have a +3 charge or higher to be considered acidic. Na+ has only a +1 charge and is a neutral ion so it will not contribute to the pH of the solution

Calculate the initial amounts of H2PO3- and NaOH in moles before the reaction happens.

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###### Problem Details

Phosphorous acid, H3PO4(aq), is a diprotic oxyacid that is an important compound in industry and agriculture.

pKa1 = 1.30
pKa2 = 6.70

Calculate the pH for each of the following points in the titration of 50.0 mL of a 1.5 M H3PO3(aq) with 1.5 M KOH(aq).

Part E. after addition of 100.0 mL of KOH