equilibria of weak acids and bases n.
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Equilibria of Weak Acids and Bases. Strong/Weak Acids. Strong HBr, HI, HCl, HNO 3 , H 2 SO 4 , HClO 4 Readily transfer H + ion to water Completely dissociated Strong electrolyte Weak HC 2 H 3 O 2 , HCN, HNO 2 , HClO, HCO 3 - Does not readily transfer H+ ion Most remains un-ionized.

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strong weak acids
Strong/Weak Acids
  • Strong
    • HBr, HI, HCl, HNO3, H2SO4, HClO4
    • Readily transfer H+ ion to water
    • Completely dissociated
    • Strong electrolyte
  • Weak
    • HC2H3O2, HCN, HNO2, HClO, HCO3-
    • Does not readily transfer H+ ion
    • Most remains un-ionized
strong weak bases
Strong/Weak Bases
  • Strong, CaO
    • Strong affinity for H+ ions
    • Some substance that readily yield OH- ions
    • Good electrolyte
  • Weak
    • Weak affinity for H+ ions
    • Some substance react only partially with water to form OH- ions
strength of conjugate acid base pairs
Strength of Conjugate Acid-Base Pairs
  • Stronger the acid, the weaker the conjugate base
  • Stronger the base, the weaker the conjugate acid
acid dissociation constant
Acid Dissociation Constant
  • Quantifies the strength of an acid
  • Use HA to represent acid molecule
  • HA (aq) + H2O (l) H3O+ (aq) + A- (aq)
  • Keq = [H3O+][A-]/[HA][H2O]
  • Water is essentially a constant in dilute solutions, therefore
  • Keq [H2O] = [H3O+][A-]/[HA]
acid dissociation constant1
Acid Dissociation Constant
  • Keq [H2O] = Ka = dissociation constant
  • For any acid, Ka = [H3O+][A-]/[HA]
  • The greater Ka, the stronger the acid
  • All weak acids Ka < 1
  • For polyprotic acids, dissociation takes place in separate steps. Each dissociation has its own Ka.
polyprotic acid dissociation
Polyprotic acid dissociation
  • Dissociation of carbonic acid
  • Step 1:

H2CO3 (aq) + H2O (l) H3O+ (aq) + HCO3- (aq)

  • Ka1 = [H3O+][HCO3-]/[H2CO3] = 4.5 x 10-7
  • Step 2:

HCO3- (aq) + H2O (aq) H3O+ (aq) + CO32-

  • Ka2 = [H3O+][CO32-]/[HCO3-] = 5.6 x 10-11
  • Ka is very small, therefore weak acid
base dissociation constant
Base Dissociation Constant
  • Kb
  • B (aq) + H2O (l) HB+ (aq) + OH- (aq)
  • Kb = [HB+][OH-]/[B]