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Polyprotic acids

Polyprotic acids. Since pK a values are generally well-separated, only 1 or 2 species will be present at significant concentration. H 3 PO 4 + H 2 O = H 2 PO 4 - + H 3 O + pK a1 = 2.1 H 2 PO 4 - + H 2 O = HPO 4 2- + H 3 O + pK a1 = 7.4

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Polyprotic acids

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  1. Polyprotic acids Since pKa values are generally well-separated, only 1 or 2 species will be present at significant concentration H3PO4 + H2O = H2PO4- + H3O+ pKa1 = 2.1 H2PO4- + H2O = HPO42- + H3O+ pKa1 = 7.4 HPO42- + H2O = PO43- + H3O+ pKa1 = 12.7

  2. Common acids • HNO3 NO3 • Nitric acid Nitrate • HNO2 NO2 • Nitrous acid Nitrite • H3PO4 PO43 • Phosphoric acid Phosphate • H3PO3 HPO32 • Phosphorous acid Phosphite • H2SO4 SO42 • Sulfuric acid Sulfate • H2SO3 SO32 • Sulfurous acid Sulfite • HClO4 ClO4 • Perchloric acid Perchlorate • HClO3 ClO3 • Chloric acid Chlorate • HClO2 ClO2 • Chlorous acid Chlorite • HOCl OCl • Hypochlorous acid Hypochlorite

  3. Anhydrides • Ex: H2O + SO3= H2SO4 • anhydride acid form • Acidic • SO3 / H2SO4 • “P2O5” / H3PO4 • CO2/H2CO3 • Basic • Na2O / NaOH • Amphoteric • Al2O3 / Al(OH)3

  4. Trends in acidity

  5. Pauling’s rules for pKa‘s of oxoacids • Write formula as MOp(OH)q • pKa 8 – 5p • Each succeeding deprotonation increases the pKa by 5 • Ex: rewrite HNO3 as NO2(OH) • p = 2; pKa 8 – 5(2)  2 (exptl value is 1.4) • Ex: rewrite H3PO4 as PO(OH)3 • p = 1; pKa1 8 – 5(1)  3 (exptl value is 2.1) • pKa2 8 (exptl value is 7.4) • pKa3 13 (exptl value is 12.7)

  6. pKa values • p Pauling pKa • calcn exptl • Cl(OH) 0 8 7.5 • ClO(OH) 1 3 2.0 • ClO2(OH) 2 2 1.2 • ClO3(OH) 3 7 ≈ 10 HlO4 + 2H2O  H5IO6

  7. Aqueous chemistry: • Fe(NO3)3 [Fe(OH2)6]3+(aq) + 3 NO3(aq) • 2 [Fe(OH2)6]3+ (aq) = [Fe2(OH2)10OH]5+ (aq) + H3O+(aq) • Hexaaquairon(III), pKa ~ 3 H2O Acid/base chemistry of complexes dimer

  8. A + :B = A:B • LA LB complex • LA = e pr acceptor; LB = e pr donor • Lewis definition is more general than BL definition, does not require aqueous or protic solvent • Ex: W + 6 :CO = [W(CO)6] • BCl3 + :OEt2 = BCl3:OEt2 • Fe3+(g) + 6 :OH2 → [Fe(OH2)6]3+  Lewis acids and bases

  9. log K and ligand type

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