# Problem: Potassium hydrogen phthalate, known as KHP (molar mass = 204.22 g/mol), can be obtained in high purity and is used to determine the concentration of solutions of strong bases by the reactionHP- (aq) + OH-(aq) → H2O(l) + P2-(aq)If a typical titration experiment begins with approximately 0.5 g KHP and has a final volume of about 100 mL, what is an appropriate indicator to use? The pKa for HP - is 5.51.

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###### FREE Expert Solution

0.0245 M

${\mathbf{K}}_{\mathbf{a}}\mathbf{=}{\mathbf{10}}^{\mathbf{-}{\mathbf{pK}}_{\mathbf{a}}}\mathbf{=}{\mathbf{10}}^{\mathbf{-}\mathbf{5}\mathbf{.}\mathbf{51}}\mathbf{=}$3.09×10-6

${\mathbf{K}}_{\mathbf{b}}\mathbf{=}\frac{{\mathbf{K}}_{\mathbf{w}}}{{\mathbf{K}}_{\mathbf{a}}}\mathbf{=}\frac{\mathbf{1}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{14}}}{\mathbf{3}\mathbf{.}\mathbf{09}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{6}}}\mathbf{=}$3.24×10-9

Reaction: HP(aq) + OH-(aq) → H2O(l) + P2-(aq)

Construct an ICE Chart:

$\overline{){{\mathbf{K}}}_{{\mathbf{b}}}{\mathbf{=}}\frac{\mathbf{products}}{\mathbf{reactants}}{\mathbf{=}}\frac{\left[{\mathrm{HP}}^{-}\right]\left[{\mathrm{OH}}^{-}\right]}{\left[{P}^{2-}\right]}}$

###### Problem Details

Potassium hydrogen phthalate, known as KHP (molar mass = 204.22 g/mol), can be obtained in high purity and is used to determine the concentration of solutions of strong bases by the reaction

HP(aq) + OH-(aq) → H2O(l) + P2-(aq)

If a typical titration experiment begins with approximately 0.5 g KHP and has a final volume of about 100 mL, what is an appropriate indicator to use? The pKa for HP - is 5.51.