In each pair, select the stronger acid. (a) Pyruvic acid (p Ka=2.49) or lactic acid (p Ks=3.08)

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In each pair, select the stronger acid. (a) Pyruvic acid (p...

In each pair, select the stronger acid. (a) Pyruvic acid $\left(\mathrm{p} K_{\mathrm{a}}=2.49\right)$ or lactic acid $\left(p K_{s}=3.08\right)$ (b) Citric acid $\left(\mathrm{p} K_{\mathrm{a}}=3.08\right)$ or phosphoric acid $\left(p K_{a}=2.10\right)$ (c) Benzoic acid $\left(K_{\mathrm{a}}=6.5 \times 10^{-5}\right)$ or lactic acid $\left(K_{\mathrm{a}}=8.4 \times 10^{-4}\right)$ (d) Carbonic acid $\left(K_{2}=4.3 \times 10^{-7}\right)$ or boric acid $\left(K_{\mathrm{a}}=7.3 \times 10^{-10}\right)$

In each pair, select the stronger acid.
(a) Pyruvic acid $\left(\mathrm{p} K_{\mathrm{a}}=2.49\right)$ or lactic acid $\left(p K_{s}=3.08\right)$
(b) Citric acid $\left(\mathrm{p} K_{\mathrm{a}}=3.08\right)$ or phosphoric acid $\left(p K_{a}=2.10\right)$
(c) Benzoic acid $\left(K_{\mathrm{a}}=6.5 \times 10^{-5}\right)$ or lactic acid $\left(K_{\mathrm{a}}=8.4 \times 10^{-4}\right)$
(d) Carbonic acid $\left(K_{2}=4.3 \times 10^{-7}\right)$ or boric acid $\left(K_{\mathrm{a}}=7.3 \times 10^{-10}\right)$

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Key Concepts

Acid Strength and pKa Values

Acid strength is generally quantified using the acid dissociation constant (Ka) or its logarithmic counterpart, the pKa. A lower pKa value indicates a stronger acid because it implies that the acid more readily donates its proton in solution. Thus, comparing pKa values is a straightforward way to determine which acid in a pair is stronger.

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, measures the extent to which an acid dissociates into its ions in solution. A larger Ka value signifies a greater tendency to lose a proton, thereby indicating a stronger acid. Comparisons using Ka values complement those made using pKa values since they are directly related through their logarithmic relationship.

Conjugate Base Stability

The strength of an acid is also influenced by the stability of its conjugate base. Once an acid donates a proton, the more stable the resulting conjugate base, the stronger the acid. Stability factors for the conjugate base include resonance stabilization, inductive effects, and the electronegativity of atoms, which help distribute and stabilize the negative charge.

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