Theories of Acids and Bases

Arrhenius Acid Substance that contains hydrogen & ionizes to produce H+ as the only positive ion in aqueous solution. HCl(g)  H+(aq) + Cl-(aq) HNO3  H+(aq) + NO3-(aq)

Arrhenius Base A substance that contains a hydroxide group & ionizes to produce OH- as the only negative ion in aqueous solution. NaOH(s)  Na+(aq) + OH-(aq)

Arrhenius Salt Electrolytes where H+ is not the only positive ion and OH- is not the only negative ion in aq. solution. Ex: NaCl, CaBr2,KNO3, NH4I

Salts in Water NaCl(s)  Na+(aq) + Cl-(aq) CaBr2(s)  Ca+2(aq) + 2Br-(aq) KNO3(s)  K+(aq) + NO3-(aq) NH4I(s)  NH4+(aq) + I-(aq) Memory Jogger

Arrhenius Model has limitations Don’t always use H2O as the solvent. Arrhenius model only applies when H2O is the solvent. Doesn’t explain all cases: NH3 doesn’t contain OH- but it produces OH-.

Alternate Theory: Bronsted-Lowry Acid = a proton donor All Arrhenius acids are Bronsted-Lowry Acids. HX(g) + H2O(l)  H3O+ + X- H+ forms a molecule-ion bond with the water molecule  H3O+, named hydronium ion.

Bronsted-Lowry Acids HCl + H2O  H3O+ + Cl- HNO3 + H2O  H3O+ + NO3- H2SO4 + H2O  H3O+ + HSO4- HSO4- + H2O  H3O+ + SO4-2

Bronsted-Lowry Base Base = proton acceptor. OH- is a base. H+ + OH-  H2O Not restricted to aqueous solution. NH3 + H2O  NH4+ + OH- NH3 is a base!

Amphoteric Substance that can act as both an acid & a base Water is amphoteric HX(g) + H2O(l)  H3O+ + X- } H20 = base NH3 + H2O  NH4+ + OH- } H2O = acid

Water is amphoteric!

Conjugate Acid / Conjugate Base HX + H2O  H3O+ + X- Acid Base Conjugate Acid Conjugate Base Conjugate Acid & Conjugate Base always on product side. Conjugate Acid = species that got the H+ Conjugate Base = species that lost the H+

Bronsted-Lowry Acids & Bases

Identify A., B., C.A., & C.B. NH3 + H2O  NH4+ + OH- HCl + H2O  H3O+ + Cl- HSO4- + H2O  SO4-2 + H3O+ NH3 + H2S  NH4+ + HS- Base Acid C. Acid C. Base C. Base Acid Base C. Acid Acid Base C. Base C. Acid Base Acid C. Acid C. Base

Lewis Definition NH3 + H2O  NH4+ + OH- Lewis acid-base theory focuses on the exchange of electron pairs rather than protons to classify as acid or base. Based on bonding and structure Includes substances that do NOT contain hydrogen ions. NH3 + H2O  NH4+ + OH-

Lewis Acids & Bases A Lewis acid is an atom, ion, or molecule that is an electron-pair acceptor. Associate: Bronsted-Lowry acid with: proton donor Bronsted-Lowry base with: proton acceptor Lewis acid with: electron pair acceptor Lewis base with: electron pair donor