Appendix I: Ionization Constants of Weak Acids

Ionization Constants of Weak Acids

Table I.1: Ionization Constants of Weak Acids
Acid Formula Ka at 25 °C Lewis Structure
acetic CH3CO2H 1.8 × 10−5 This image represents the Lewis structure for acetic acid. This acid is made up of a 2 carbon chain with a carboxylic acid functional group. This consists of an end carbon double bonded to an oxygen and also bonded to an OH group.
arsenic H3AsO4 5.5 × 10−3 This image represents the Lewis structure for acidic arsenic. This acid is made up of arsenic as the central atom, double bonded to an oxygen and single bonded to 3 OH groups.
This is the chemical formula for dihydrogen arsenate. 1.7 × 10−7
This is the chemical formula for hydrogen arsenate. 5.1 × 10−12
arsenous H3AsO3 5.1 × 10−10 This image represents the Lewis structure for arsenous acid. This acid is made up of arsenic as the central atom, single bonded to 3 oxygen atoms and also containing a single lone pair of electrons.
boric H3BO3 5.4 × 10−10 This image represents the Lewis structure for boric acid. This acid is made up of boron as the central atom, single bonded to 3 oxygen atoms.
carbonic H2CO3 4.3 × 10−7 This image represents the Lewis structure for carbonic acid. This acid is made up of carbon as the central atom, single bonded to 2 OH (hydroxide) groups and double bonded to an oxygen atom.
This is the chemical formula for bicarbonate. 5.6 × 10−11
cyanic HCNO 2 × 10−4 This image represents the Lewis structure for cyanic acid. This acid is made up of carbon as the central atom, double bonded to an oxygen atom and a nitrogen atom on opposite sides of the carbon.
formic HCO2H 1.8 × 10−4 This image represents the Lewis structure for formic acid. This acid is made up of carbon as the central atom, single bonded to an OH (hydroxide) group an oxygen atom, and a single hydrogen atom.
hydrazoic HN3 2.5 × 10−5 This image represents the Lewis structure for hydrazoic acid. This acid is made up of nitrogen as the central atom, single bonded to another nitrogen atom and triple bonded to yet another nitrogen atom. This molecule also converts to a central nitrogen double bonded to two nitrogen's on either side.
hydrocyanic HCN 4.9 × 10−10
hydrofluoric HF 3.5 × 10−4
hydrogen peroxide H2O2 2.4 × 10−12 This image represents the Lewis structure for hydrogen peroxide. This acid is made up of two oxygen's single bonded to one another each bonded to one hydrogen and each having two lone pairs of electrons.
hydrogen selenide H2Se 1.29 × 10−4
HSe 1 × 10−12
hydrogen sulfate ion This is the chemical formula for hydrogen sulfate also called bisulfate. 1.2 × 10−2 This image represents the Lewis structure for hydrogen sulfate ion. This acid is made up of sulfur as the central atom, single bonded to an OH (hydroxide) group, single bonded to an oxygen ion and double bonded to two oxygen atoms.
hydrogen sulfide H2S 8.9 × 10−8
HS 1.0 × 10−19
hydrogen telluride H2Te 2.3 × 10−3
HTe 1.6 × 10−11
hypobromous HBrO 2.8 × 10−9
hypochlorous HClO 2.9 × 10−8
nitrous HNO2 4.6 × 10−4 This image represents the Lewis structure for nitrous acid. This acid is made up of nitrogen as the central atom, single bonded to an OH (hydroxide) group and single bonded to an oxygen atom.
oxalic H2C2O4 6.0 × 10−2 This image represents the Lewis structure for oxalic acid. This acid is made up of a two carbon chain. Each carbon is double bonded to an oxygen atom and single bonded to an OH (hydroxide) group.
This is the chemical formula for oxalic acid. 6.1 × 10−5
phosphoric H3PO4 7.5 × 10−3 This image represents the Lewis structure for phosphoric acid. This acid is made up of phosphorous as the central atom, single bonded to three OH (hydroxide) groups and double bonded to an oxygen atom.
This is the chemical formula for dihydrogen phosphate. 6.2 × 10−8
This is the chemical formula for hydrogen phosphate. 4.2 × 10−13
phosphorous H3PO3 5 × 10−2 This image represents the Lewis structure for phosphorous acid. This acid is made up of phosphorous as the central atom, single bonded to three OH (hydroxide) groups.
This is the chemical formula for dihydrogen phosphite. 2.0 × 10−7
sulfurous H2SO3 1.6 × 10−2 This image represents the Lewis structure for sulfurous acid. This acid is made up of sulfur as the central atom, single bonded to two OH (hydroxide) groups and single bonded to an oxygen atom. The central sulfur also has one lone pair of electrons.
This is the chemical formula for hydrogen sulfite. 6.4 × 10−8

Attribution & References

Except where otherwise noted, this page is adapted from “Appendix H: Ionization Constants of Weak Acids” In General Chemistry 1 & 2 by Rice University, a derivative of Chemistry (Open Stax) by Paul Flowers, Klaus Theopold, Richard Langley & William R. Robinson and is licensed under CC BY 4.0. ​Access for free at Chemistry (OpenStax)

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Enhanced Introductory College Chemistry Copyright © 2023 by Gregory Anderson; Caryn Fahey; Jackie MacDonald; Adrienne Richards; Samantha Sullivan Sauer; J.R. van Haarlem; and David Wegman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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