Polyprotic Acid Video Lessons

Concept:

# Problem: Calculate the [H3O+] of the following polyprotic acid solution: 0.145M H3C6H5O7.Calculate the pH of this solution.

###### FREE Expert Solution

Since we’re dealing with a weak acid, we will have to create an ICE chart to determine the equilibrium concentration of each species:

$\overline{){\mathbf{K}}{\mathbf{=}}\frac{\mathbf{p}\mathbf{r}\mathbf{o}\mathbf{d}\mathbf{u}\mathbf{c}\mathbf{t}\mathbf{s}}{\mathbf{r}\mathbf{e}\mathbf{a}\mathbf{c}\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{t}\mathbf{s}}}$

Solids and liquids are not included in the expression

${\mathbit{K}}_{\mathbf{1}}\mathbf{=}\frac{\left[{\mathbf{H}}_{\mathbf{2}}{\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}{{\mathbf{O}}_{\mathbf{7}}}^{\mathbf{-}}\right]\left[{\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}\right]}{\left[{\mathbf{H}}_{\mathbf{3}}{\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}{\mathbf{O}}_{\mathbf{7}}\right]}\phantom{\rule{0ex}{0ex}}\mathbf{8}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{4}}\mathbf{=}\frac{\left(\mathbf{x}\right)\left(\mathbf{x}\right)}{\left(\mathbf{0}\mathbf{.}\mathbf{145}\mathbf{-}\mathbf{x}\right)}\phantom{\rule{0ex}{0ex}}\mathbf{8}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{4}}\mathbf{=}\frac{{\mathbf{x}}^{\mathbf{2}}}{\mathbf{\left(}\mathbf{0}\mathbf{.}\mathbf{145}\mathbf{-}\mathbf{x}\mathbf{\right)}}$

Check if the x in the denominator can be ignored

since 172 < 500, x in the denominator cannot be ignored

$\left\{8.4×{10}^{-4}=\frac{{x}^{2}}{\overline{)\left(0.145-x\right)}}\right\}\overline{)\mathbf{\left(}\mathbf{0}\mathbf{.}\mathbf{145}\mathbf{-}\mathbf{x}\mathbf{\right)}}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\left(8.4×{10}^{-4}\right)\left(0.145-x\right){\mathbf{=}}{{\mathbf{x}}}^{{\mathbf{2}}}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}{\mathbf{1}}{\mathbf{.}}{\mathbf{218}}{\mathbf{×}}{{\mathbf{10}}}^{\mathbf{-}\mathbf{4}}{\mathbf{-}}\mathbf{\left(}\mathbf{8}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{4}}\mathbf{\right)}{\mathbf{x}}{\mathbf{=}}{{\mathbf{x}}}^{{\mathbf{2}}}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}{{\mathbf{x}}}^{{\mathbf{2}}}{\mathbf{+}}\mathbf{\left(}\mathbf{8}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{4}}\mathbf{\right)}{\mathbf{x}}{\mathbf{-}}{\mathbf{1}}{\mathbf{.}}{\mathbf{218}}{\mathbf{×}}{{\mathbf{10}}}^{\mathbf{-}\mathbf{4}}{\mathbf{=}}{\mathbf{0}}$

Solve for x using the quadratic formula:

98% (444 ratings)
###### Problem Details

Calculate the [H3O+] of the following polyprotic acid solution: 0.145M H3C6H5O7.

Calculate the pH of this solution.

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Polyprotic Acid concept. You can view video lessons to learn Polyprotic Acid. Or if you need more Polyprotic Acid practice, you can also practice Polyprotic Acid practice problems.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Falconer's class at Colorado School of Mines.