The Acid Constants for Some Acids at 25°C.

Acid	Formula and Ionization Equation	Ka
Acetic	CH3COOH + H2OH3O+ + CH3COO–	1.8 × 10–5
Aluminum ion	Al(H2O)63+ + H2O  H3O+ + Al(H2O)5OH2+	7.2 × 10–6
Ammonium ion	NH4+ + H2OH3O+ + NH3	5.6 × 10–10
Arsenic	H3AsO4 + H2O H3O+ + H2AsO–4 H2AsO–4 + H2OH3O+ + HAsO2–4 HAsO2–4 + H2O  H3O+ + AsO3–4	K1 = 6.17 × 10 –3K2 = 1.17 × 10–7 K3 = 3.09 × 10–12
Benzoic	C6H5COOH + H2O H3O+ + C6H5COO–	1.2 × 10–4
Boric	B(OH)3(H2O) + H2OH3O+ + B(OH)–4	5.8 × 10–10
Carbonic	H2CO3 + H2O H3O+ + HCO–3HCO–3 + H2O H3O+ + CO2–3	K1 = 4.3 × 10–7K2 = 4.7 × 10–11
Citric	H3C6H5O7 + H2O H3O+ + H2C6H5O–7 H2C6H5O–7 + H2O  H3O+ + HC6H5O2–7 HC6H5O2–7 + H2O H3O+ + C6H5O3–7	K1 = 1.4 × 10 –3K2 = 4.5 × 10–5 K3 = 1.5 × 10–6
Formic	HCOOH + H2O  H3O+ + HCOO–	3.0 × 10–4
Hexaaquaaluminum ion		1.0 × 10–5
Hexaaquacopper (II) ion		4.57 × 10–8
Hexaaquairon (II) ion		2.63 × 10–10
Hexaaquairon (III) ion		6.76 × 10–3
Hexaaqualead (II) ion		1.38 × 10–8
Hexaaquanickel (II) ion		1.38 × 10–10
Hydrazoic	HN3 + H2O  H3O+ + N–3	1.0 × 10–5
Hydrochloric	HCl + H2O  H3O+ + Cl–	very large
Hydrocyanic	HCN + H2O  H3O+ + CN–	3.3 × 10–10
Hydrofluoric	HF + H2O  H3O+ + F–	6.8 × 10–4
Hydrogen peroxide	H2O2 + H2O  H3O+ + HO–2	2.1 × 10–12
Hydrosulfuric	H2S + H2O  H3O+ + HS–HS– + H2O  H3O+ + S2–	K1 = 1 × 10–7K2 = 1 × 10–19
Hypochlorous	HOCl + H2O H3O+ + OCl–	6.8 × 10–8
Nitric	HNO3 + H2O H3O+ + NO3–	27.5
Lactic		1.48 × 10–4
Nitrous		7.11 × 10–4
Oxalic	H2C2O4 + H2O  H3O+ + HC2O–4HC2O–4 + H2O H3O+ + C2O2–4	K1 = 5.5 × 10–2 K2 = 1.4 × 10–4
Perchloric		131.8
Phenol	HC6H5O + H2O H3O+ + C6H5O–	1.7 × 10–10
Phosphoric	H3PO4 + H2O  H3O+ + H2PO–4 H2PO–4 + H2O  H3O+ + HPO2–4 HPO2–4 + H2O H3O+ + PO3–4	K1 = 7.2 × 10 –3K2 = 6.3 × 10–8 K3 = 4.6 × 10–13
Phosphorous	H3PO3 + H2O H3O+ + H2PO–3H2PO–3 + H2O  H3O+ + HPO2–3	K1 = 2.4 × 10–2K2 = 2.9 × 10–7
Propanoic		1.32 × 10–5
Selenic	H2SeO4 + H2OH3O+ + HSeO–4HSeO–4 + H2O  H3O+ + SeO2–4	K1 = very largeK2 = 2.2 × 10–2
Selenous	H2SeO3 + H2O  H3O+ + HSeO–3HSeO–3 + H2O  H3O+ + SeO2–3	K1 = 2.5 × 10–3K2 = 1.6 × 10–9
Sulfuric	H2SO4 + H2O  H3O+ + HSO–4HSO–4 + H2O H3O+ + SO2–4	K1 = very largeK2 = 1.1 × 10–2
Sulfurous	H2SO3 + H2O  H3O+ + HSO–3HSO–3 + H2O  H3O+ + SO2–3	K1 = 1.7 × 10–2K2 = 6.3 × 10–8
Tellurous	H2TeO3 + H2O H3O+ + HTeO–3HTeO–3 + H2O H3O+ + TeO2–3	K1 = 1.9 × 10–3K2 = 4.6 × 10–10

• Taken from Hogfelt, E. Perrin, D. D. Stability Constants of Metal Ion Complexes, 1^st ed. Oxford; New Pergamon, 1979-1982. International Union of Pure and Applied Chemistry, Commission on Equilibrium. ISBN: 0080209580