We are being asked to calculate the **K _{a} of lactic acid**.

Recall: Weak acids possess a **K _{a}**

The equilibrium expressions of K_{a} and K_{b} are the same as other equilibrium constants we’ve seen.

For **weak acids**, their equilibrium constant is

$\overline{){{\mathbf{K}}}_{{\mathbf{a}}}{\mathbf{=}}\frac{\mathbf{products}}{\mathbf{reactants}}{\mathbf{}}{\mathbf{=}}\frac{\left[{\mathbf{A}}^{\mathbf{-}}\right]\left[{\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}\right]}{\mathbf{\left[}\mathbf{HA}\mathbf{\right]}}}$

For **weak bases**, their equilibrium constant is

$\overline{){{\mathbf{K}}}_{{\mathbf{b}}}{\mathbf{=}}\frac{\mathbf{products}}{\mathbf{reactants}}{\mathbf{}}{\mathbf{=}}\frac{\left[{\mathbf{OH}}^{\mathbf{-}}\right]\left[\mathbf{HA}\right]}{\mathbf{\left[}{\mathbf{A}}^{\mathbf{-}}\mathbf{\right]}}}$

The greater the K_{a} value the stronger the acid, while the greater the K_{b} the stronger the base.** **

**K**_{a}** **and **K**_{b} are connected by the following equation:

$\overline{){{\mathbf{K}}}_{{\mathbf{w}}}{\mathbf{=}}{{\mathbf{K}}}_{{\mathbf{a}}}{\mathbf{\times}}{{\mathbf{K}}}_{{\mathbf{b}}}}$

where K_{w} = 1 x 10^{-14 }

It can be found in textbooks or on the internet.

We are given a saturated solution of **calcium lactate salt with [Ca ^{2+}]=0.26 M and a pH=8.40**.

The dissociation of calcium lactate salt in water is:

**Ca(Lact) _{2(s) }+ H_{2}O_{(l)}**

Lactic acid is a weak acid found in milk. Its calcium salt is a source of calcium for growing animals. A saturated solution of this salt, which we can represent as Ca(Lact)_{2} has a [Ca^{2+}]=0.26 M and a pH=8.40.

Assuming the salt is completely dissociated, calculate the K_{a} of lactic acid.

Frequently Asked Questions

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 Weak Acids concept. If you need more Weak Acids practice, you can also practice Weak Acids practice problems.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Morkowchuk's class at UVA.