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Acid / Base

. Acid / Base. Arrhenius definition. produces H + in water. acid. base. produces OH - in water. . . H +. + A -. HA. + H 2 O. K a = [ H + ] [A - ]. K a. strength of acid. [HA] [H 2 O]. [HA]. strong acids. no K a. weak acids. dissociate completely. equilibrium process.

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Acid / Base

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  1. Acid/Base Arrhenius definition produces H+ in water acid base produces OH- in water   H+ + A- HA + H2O Ka = [H+] [A-] Ka strength of acid [HA] [H2O] [HA] strongacids no Ka weak acids dissociate completely equilibrium process HCl, HBr, HI HF Ka = 6.8 x 10-4 HNO3, HIO3 Ka = 0.16 HClO4, H2SO4

  2. Acid/Base Arrhenius definition produces H+ in water acid base produces OH- in water  + OH- (aq) Na+(aq) NaOH (s) + H2O  NH3 (g) + H2O NH4+ (aq) + OH- (aq) Kb strong bases weak bases OH- Group I NH3 Kb= 1.8 x 10-5 Group II R-NH2 amines O2- (Ca, Sr, Ba)

  3. .. .. H Cl + H O .. H O H H H Brønsted-Lowry Acids and Bases acid proton donor H .. proton acceptor base + Cl- +  conjugate pair base acid strong acid very weak base conjugate pair stronger base stronger acid +

  4. Brønsted-Lowry Acids and Bases strength of acid related to stability of conjugate base conjugate bases carry negative charges stabilized by: related to size (LDF) polarizability electronegativity inductive effect e- in resonance HI  H+ + I- 5p orbital largest orbital most stable HBr  H+ + Br- 4p orbital strongest acid HCl  H+ + Cl- 3p orbital HF  H+ + F- 2p orbital

  5. Brønsted-Lowry Acids and Bases strength of acid related to stability of conjugate base conjugate bases carry negative charges stabilized by: electronegativity with same size orbitals, electronegativity determines stability F- OH- NH2- CH3- HF > H2O NH3 CH4 > >

  6. Brønsted-Lowry Acids and Bases strength of acid related to stability of conjugate base conjugate bases carry negative charges inductive effect related to electronegativity – but atom near charge more stable base stronger acid

  7. Brønsted-Lowry Acids and Bases strength of acid related to stability of conjugate base conjugate bases carry negative charges resonance HNO3 HNO2 For oxoacids with same central atom, more O means stronger acid For oxoacids with same number of O, more electronegative central atom means stronger acid

  8. .. H H O .. .. .. + H N H H N H H O - H .. .. H H Brønsted-Lowry Acids and Bases acid proton donor proton acceptor base +  + acid base base acid weak base relatively strong acid Kb= 1.8 x 10-5

  9. Autoionization of H2O H > 0 H+ (aq)  H2O + OH- (aq) Kw = at 25oC [H+] [OH-] = 1.0 x 10-14 [H2O] 55.5 M [H+] = [OH-] = 1.0 x 10-7 - 0.0000001 [0.1] [OH-] Kw = = 1.0 x 10-14 [OH-] = 1.0 x 10-13 Le Chatelier [OH-] decrease add H+ 0.10 mol HCl [H+] = 0.10 M = 0.1 mol H+ 1.0 L L both present in all aqueous solutions

  10. pH [H+] 10 M - 10-15 M pH = - log [H+] low pH -1 15 high pH basic acidic [H+] = = 1.0 x 10-7 neutral [OH-] pH = 7 pOH = - log [OH-] pH + pOH = 14 pH of milk = 6.4 [H+] = 3.981071706 x 10-7 -6.4 10 4 x 10-7 1 sig. fig.

  11. Brønsted-Lowry Acids and Bases acid proton donor proton acceptor base C2H3OOH CN- C2H3OO- + HCN +  base1 acid2 acid base 1 2

  12. Brønsted-Lowry Acids and Bases acid proton donor proton acceptor base Ka = 7.2 x 10-4  HF + H2O H3O+ F- + base2 acid1 base1 acid2  H2O CH3NH3+ OH- CH3NH2 + + base1 acid2 acid1 base2 H3O+ strongest acid in water H2O amphoteric OH- strongest base in water acid or base

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