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Parth Ajmera

Chemical Foundations of Life

#biochemistry#water#reference
1.0

Equations

Ionization of water

In notes →
H2O⇌H++OH−H_2O \rightleftharpoons H^+ + OH^-
  • H2OH_2O — water
  • H+H^+ — hydrogen ion (proton)
  • OH−OH^- — hydroxide ion

Autoionization of water

In notes →
2H2O⇌H3O++OH−2H_2O \rightleftharpoons H_3O^+ + OH^-
  • H3O+H_3O^+ — hydronium ion, water's conjugate acid
  • OH−OH^- — hydroxide ion, water's conjugate base

Equilibrium constant of water's ionization

In notes →
Keq=[H+][OH−][H2O]K_{eq} = \dfrac{[H^+][OH^-]}{[H_2O]}
  • KeqK_{eq} — equilibrium constant of water's ionization, mol/L
  • [H+][H^+] — hydrogen ion concentration, mol/L
  • [OH−][OH^-] — hydroxide ion concentration, mol/L
  • [H2O][H_2O] — molar concentration of water, mol/L

Ion product of water (KwK_w)

In notes →
Kw=[H+][OH−]K_w = [H^+][OH^-]
  • KwK_w — ion product of water: product of [H+][H^+] and [OH−][OH^-] in pure water, mol²/L²
  • [H+][H^+] — hydrogen ion concentration, mol/L
  • [OH−][OH^-] — hydroxide ion concentration, mol/L

pH

In notes →
pH=−log⁡[H+]pH = -\log[H^+]
  • pHpH — measure of acidity, unitless
  • [H+][H^+] — hydrogen ion concentration, mol/L

Ionization of HCl in water

In notes →
HCl⏟acid1+H2O⏟base2⇌Cl−⏟base1+H3O+⏟acid2\underbrace{HCl}_{\text{acid}_1} + \underbrace{H_2O}_{\text{base}_2} \rightleftharpoons \underbrace{Cl^-}_{\text{base}_1} + \underbrace{H_3O^+}_{\text{acid}_2}
  • HClHCl — acid 1: donates a proton to become its conjugate base, Cl−Cl^-
  • Cl−Cl^- — conjugate base of HClHCl
  • H2OH_2O — base 2: accepts a proton to become its conjugate acid, H3O+H_3O^+
  • H3O+H_3O^+ — conjugate acid of H2OH_2O

Acid dissociation constant (KaK_a)

In notes →
Ka=[H+][A−][HA]K_a = \dfrac{[H^+][A^-]}{[HA]}
  • HAHA — undissociated acid
  • H+H^+ — hydrogen ion (proton)
  • A−A^- — conjugate base of HAHA
  • KaK_a — acid dissociation constant (also acid ionization constant, or acidity constant), mol/L

pKapK_a

In notes →
pKa=−log⁡KapK_a = -\log K_a
  • pKapK_a — negative log of KaK_a, unitless
  • KaK_a — acid dissociation constant, mol/L

pH and pKapK_a — the Henderson-Hasselbalch equation

In notes →
pH=pKa+log⁡[A−][HA]pH = pK_a + \log \dfrac{[A^-]}{[HA]}
  • pHpH — measure of acidity of the solution, unitless
  • pKapK_a — acid dissociation constant of the acid in question, unitless
  • [A−][A^-] — conjugate base concentration, mol/L
  • [HA][HA] — undissociated acid concentration, mol/L
09 formulas