# 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 A. before addition of any KOH

###### FREE Expert Solution

a. before addition of any KOH

• only the acidic form exists

Equilibrium reaction:        H3PO3(aq) + H2O(l)  H2PO3-(aq)H3O+(aq)     pKa1

We will need the Ka for the reaction.

$\overline{){{\mathbf{K}}}_{{\mathbf{a}}}{\mathbf{=}}{{\mathbf{10}}}^{\mathbf{-}{\mathbf{pK}}_{\mathbf{a}}}}\phantom{\rule{0ex}{0ex}}{\mathbf{K}}_{\mathbf{a}}\mathbf{=}{\mathbf{10}}^{\mathbf{-}\mathbf{1}\mathbf{.}\mathbf{30}}$

Ka = 0.05012

$\overline{){{\mathbf{K}}}_{{\mathbf{a}}}{\mathbf{=}}\frac{\mathbf{products}}{\mathbf{reactants}}}$

Solids and liquids are ignored in equilibrium expressions

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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 A. before addition of any KOH