WEAK Acids & Bases have Ka & Kb and RICE Unit 9 SUMMARY: Acid-Base Equilibria Acid: proton (H+) donor Base: proton (H+) acceptor (forms conjugate base) (forms conjugate acid) 6 Strong Acids: (completely ionize) HCl, HBr, HI, HNO3 , H2SO4 , HClO4 8 Strong Bases: (completely dissociate) the soluble hydroxides (OH–) of… Group 1 (Li,Na,K,Rb,Cs) and Ca2+, Sr2+, Ba2+ WEAK Acids & Bases have Ka & Kb and RICE

Factors Affecting Acid Strength larger X in H–X stronger acid (bond is longer, weaker) stronger acid (greater ∆EN) more polar H–X bond (weaker, likely to break and lose H+)

Water & pH H2O(l) + H2O(l)  H3O+(aq) + OH−(aq) H2O(l)  H+(aq) + OH−(aq) Kw = [H+] [OH−] = 1.0  10–14 (at 25oC) x2 = 1.0  10–14 [H+] = √(1.0  10−14) = 1.0  10−7 pH = −log [H+] In pure water, pH = −log(1.0  10−7) = 7.00 Acids have higher [H+], so pH<7 (lower [OH–]) Bases have lower [H+], so pH>7 (higher [OH–])

pH pOH [H+] [OH–] Calculations pH = –log[H+] pOH = –log[OH–] 10–pH = [H+] 10–pOH = [OH–] Kw = [H+]∙[OH–] = 1.0 x 10–14 pH + pOH = 14 Ka  Kb = Kw (for conjugates) Given any 1 of these 4, you know all 4 values. H+ OH– pH pOH

GIVEN pH, Calculate Ka pH = −log [H3O+] 2.38 = −log [H3O+] (0.0042)2 [HCOOH] [H3O+] [HCOO−] I 0.10 M 0 M C E 0.0042 M pH = −log [H3O+] 2.38 = −log [H3O+] −2.38 = log [H3O+] 10−2.38 = [H3O+] (0.0042)2 (0.10) Ka = [H3O+]eq = 0.0042 M

HCOOH(aq) + H2O(l)  H3O+(aq) + HCOO–(aq) Percent Ionization [H3O+]eq [HA]in NOT on equation sheet % ionization =  100% HCOOH(aq) + H2O(l)  H3O+(aq) + HCOO–(aq) [HCOOH] [H3O+] [HCOO−] I 0.10 M 0 M C −0.0042 +0.0042 E 0.0958 = 0.10 M 0.0042 M 0.0042 0.10 % ionization =  100% = 4.2% 4.2% OF 0.10 M HCOOH IS ionized.

HC2H3O2(aq) + H2O(l)  H3O+(aq) + C2H3O2–(aq) GIVEN Ka , Calculate pH HC2H3O2(aq) + H2O(l)  H3O+(aq) + C2H3O2–(aq) [H3O+] [C2H3O2−] [HC2H3O2] Ka = = 1.8  10−5 [HC2H3O2] [H3O+] [C2H3O2−] I 0.30 M C E –x +x +x 0.30 – x x x  0.30 M (b/c K <<<1) (x)2 (0.30) 1.8  10−5 = x = 2.3  10−3 M H+ pH = −log [H+]

Cations: Anions: NH4+(aq) + H2O(l)  NH3(aq) + H3O+(aq) (acidic, ↓pH) (donates H+) NH4+(aq) + H2O(l)  NH3(aq) + H3O+(aq) Cations: (acidic, ↓pH) Cu+(aq) + H2O(l)  CuOH(aq) + H+(aq) Most metal cations will lower pH (acidic). (Fe3+, Zn2+, …) (take OH– from H2O to lose H+) But, metal cations of strong base CAN’T affect pH. (Li+,Na+,K+,Ca2+,Ba2+) (can’t take OH– from H2O) Anions: (basic, ↑pH) F−(aq) + H2O(l)  HF(aq) + OH−(aq) Most anions will increase pH (basic). (F–, HCO3–, NO2–) (take H+ from H2O) But, anions from conj. base of a strong acid CAN’T affect pH. (Cl–, HSO4–, NO3–) (can’t take H+ from H2O)