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 C. after addition of 50.0 mL of KOH

###### FREE Expert Solution

Part B. After addition 25.0 mL of KOH

Write the chemical equation for the reaction between H3PO3 and NaOH.

Reaction:

H3PO3(aq) + NaOH(aq) ⇌  F-­(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 H3PO3 and NaOH in moles before the reaction happens.

molarity (volume) → moles

Recall:

$\overline{){\mathbf{M}}{\mathbf{=}}\frac{\mathbf{mol}}{\mathbf{L}}}$

*convert volumes from mL to L → 1 mL = 10-3 L

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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 C. after addition of 50.0 mL of KOH