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Lactic acid is a weak acid found in milk. Its calcium salt
Chapter 15, Problem 145E(choose chapter or problem)
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 \(\mathrm{Ca}(\text { Lact })_{2}\) has a \(\left[\mathrm{Ca}^{2+}\right]=0.26 \mathrm{M}\) and a \(\mathrm{pH}=8.40\). Assuming the salt is completely dissociated, calculate the \(K_{\mathrm{a}}\) of lactic acid.
Questions & Answers
QUESTION:
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 \(\mathrm{Ca}(\text { Lact })_{2}\) has a \(\left[\mathrm{Ca}^{2+}\right]=0.26 \mathrm{M}\) and a \(\mathrm{pH}=8.40\). Assuming the salt is completely dissociated, calculate the \(K_{\mathrm{a}}\) of lactic acid.
ANSWER:Step 1 of 3
The salt is completely dissociated, thus,
\(\mathrm{Ca}(\text { Lact })_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Ca}^{2+}+2 \text { Lact }^{-}+\mathrm{OH}^{-}\)
\(\left[\text { Lact }^{-}\right]=2\left[\mathrm{Ca}^{2+}\right]=2(0.26)=0.52 \mathrm{M}\)
\(\mathrm{pH}\left(\mathrm{OH}^{-}\right)=14-8.4=5.6\)
\(\left[O H^{-}\right]=10^{0.52}=2.5 \times 10^{-6} \mathrm{M}\)