Many important biochemicals are organic acids, such as pyruvic acid (p K a = 2.50) and lactic acid (p K a = 3.86). The conjugate bases are pyruvate and lactate, respectively. For each acid, determine which form-the acid or the conjugate base-predominates at pH 7.4. A graphic shows a check mark inscribed on a colored circle. 6

Question

Chemistry

Tyrone Hamilton

21 September, 12:21

Many important biochemicals are organic acids, such as pyruvic acid (p K a = 2.50) and lactic acid (p K a = 3.86). The conjugate bases are pyruvate and lactate, respectively. For each acid, determine which form-the acid or the conjugate base-predominates at pH 7.4. A graphic shows a check mark inscribed on a colored circle. 6

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Konner Velez · Answer 1

Pyruvic acid: conjugate base

Lactic acid: conjugate base

Explanation:

The ratio of conjugate base to conjugate acid can be found using the Henderson-Hasselbalch equation when the pH and pKa are known.

pH = pKa + log ([A⁻]/[HA])

The equation can be rearranged to solve for the ratio:

pH - pKa = log ([A⁻]/[HA])

[A⁻]/[HA] = 10^ (pH-pKa)

Now we can calculate the ratio for the pyruvic acid:

[A⁻]/[HA] = 10^ (pH-pKa) = 10^ (7.4 - 2.50) = 79433

[A⁻] = 79433[HA]

There is a much higher concentration of the conjugate base.

Similarly for lactic acid:

[A⁻]/[HA] = 10^ (pH-pKa) = 10^ (7.4 - 3.86) = 3467

[A⁻] = 3467[HA]

For lactic acid the conjugate base also dominates at pH 7.4