ORG-10

Organic pKa

Ka = 10^{−pKa}. Acid dissociation of an organic acid.

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AciditypKa

Governing equation

K_a=10^{-\mathrm{p}K_a}

$\mathrm{p}K_a \in \left[-5, 50\right]$

where

\mathrm{p}K_a: pKa (—)
K_a: Ka (—)

The figure, part by part

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①

Governing law — red

K_a=10^{-\mathrm{p}K_a}

$\mathrm{p}K_a \in \left[-5, 50\right]$

$\mathrm{p}K_a = -5$ $K_a = 1\times 10^{5}$

Along the curve

②

Domain of the variable — blue

\mathrm{p}K_a_{\min} = -5,\quad \mathrm{p}K_a_{\max} = 50

$\mathrm{p}K_a \in \left[-5, 50\right]$

$\mathrm{p}K_a = -5$ $\mathrm{p}K_a = -5$

Along the curve

③

Response curve — green

K_a=10^{-\mathrm{p}K_a}

$\mathrm{p}K_a \in \left[-5, 50\right]$

$\mathrm{p}K_a = -5$ $K_a = 1\times 10^{5}$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}K_a}{\mathrm{d}\mathrm{p}K_a}

$\mathrm{p}K_a \in \left[-5, 50\right]$

$\mathrm{p}K_a = -4.654$ $K_a^{\prime} = -1.15\times 10^{5}$

Along the curve

Lecture brief

Historical brief

Hammett (1937) and Taft linear free-energy, E-factor green metrics, Woodward–Fieser UV and Claisen equilibria are how organic chemistry became predictive. The lab is substituent, waste and tautomer. This sheet (ORG-10 — Organic pKa) is the form associated with pKa. Working symbols: $\mathrm{p}K_a$ $\rightarrow$ $K_a$ . Lower pKa is stronger acid. Phenol ~10, acetic ~4.8, TFA ~0.2.

Purpose

Purpose: compute

K_a

from

\mathrm{p}K_a

in Organic chemistry via

K_a=10^{-\mathrm{p}K_a}

Ka = 10^{−pKa}. Acid dissociation of an organic acid. Use it when a real organic chemistry question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

\mathrm{p}K_a = 4.760\,\mathrm{—}

, the governing relation

K_a=10^{-\mathrm{p}K_a}

yields

K_a = 1.738e-5\,\mathrm{—}

. Aqueous, 25 °C snapshot. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

pKa \mathrm{p}K_a4.76 —

Outputs

Ka K_a0.000017 —

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Narration of this film

Aqueous, 25 °C snapshot.

Lower pKa is stronger acid. Phenol ~10, acetic ~4.8, TFA ~0.2.

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