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Acid-Base and Donor-Acceptor Chemistry. Chapter 6. Acids and Bases. The Major Acid-Base Definitions:. Acids and Bases. Arrhenius: Acid is proton source in water, base is hydroxide source Acid + Base = Salt + Water; HCl + NaOH NaCl + H 2 O Works in aqueous solutions only
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Acid-Base and Donor-Acceptor Chemistry Chapter 6
Acids and Bases The Major Acid-Base Definitions:
Acids and Bases • Arrhenius:Acid is proton source in water, base is hydroxide sourceAcid + Base = Salt + Water; HCl + NaOH NaCl + H2OWorks in aqueous solutions only • Brønsted-Lowry:Acid is proton donor, base is proton acceptorAcid(1) + Base(1) Acid(2) + Base(2) Can this happen without water? • Conjugate acid-base pairsReaction favors the weaker acid/base pairNon-aqueous solvents, gas and solid phase reactions
Acids and Bases • Solvent system definition: If a species can autoionize (autodissociate, form a cation and an anion), the cation is an acid and the anion is a base • In this system, an acid increases [cation] and a base increases [anion] Water: 2 H2O H3O+ + OH– • HCl is an acid in this solvent system (increases [cation])HCl + H2O H3O+ + Cl–
Protic Acids and Bases • Kion is K for the autoionization of the pure solvent Solvent Acid Base pKionH2SO4 H3SO4+ HSO4– 3.4 at 10 ºCH2O H3O+ OH– 14NH3 NH4+ NH2– 27 • Acetic acid is acid in water, but base in H2SO4 CH3CO2H + H2SO4 HSO4– + CH3CO2H2+ • Urea is a base in water, but an acid in liquid NH3 (NH2)2CO + NH3 NH4+ + (NH2)(NH)CO–
Measuring Lewis Acid-Base Interaction Strength via Electronic Spectra
Hard and Soft Acids and BasesExamples: Ionic Compound Solubility AgF(s) + H2O(l) Ag+(aq) + F-(aq) Ksp = 205 AgCl(s) + H2O(l) Ag+(aq) + Cl-(aq) Ksp = 1.8 x 10-10 AgBr(s) + H2O(l) Ag+(aq) + Br-(aq) Ksp = 5.2 x 10-13 AgI(s) + H2O(l) Ag+(aq) + I-(aq) Ksp = 8.3 x 10-17 Similarly, solubility: Hg2F2 > Hg2Cl2 > Hg2Br2 > Hg2I2 BUT, LiF < LiI MgF2 is less soluble than MgCl2 AlF3 is less soluble than AgCl3
Hard and Soft Acids and BasesExamples: Thiocyanate Bonding to Metals SCN- can bond through S or N S-binding with M = large, polarizable metals like Hg2+, Au+, Pd2+ N-binding with M = smaller, less polarizable metals: Zn2+, Ni2+
Hard and Soft Acids and BasesDefinitions Hard base: small, not polarizable Soft base: large, highly polarizable
Hard and Soft Acids and BasesDefinitions Hard acid: small, not polarizable Soft acid: large, highly polarizable