Transcript Slide 1
Acid/Base Arrhenius definition acid base produces H+ in water produces OH- in water H + + AHA + H2O Ka = [H+] [A-] [HA] [H2O] [HA] strong acids no Ka dissociate completely HCl, HBr, HI HNO3, HClO4, H2SO4 Ka strength of acid weak acids equilibrium process HF Ka = 6.8 x 10-4 HIO3 Ka = 0.16 Acid/Base Arrhenius definition acid base produces H+ in water produces OH- in water NaOH (s) + H2O Na+(aq) + OH- (aq) NH3 (g) + H2O NH4+ (aq) + OH- (aq) Kb strong bases weak bases OH- Group I O2- Group II (Ca, Sr, Ba) NH3 Kb = 1.8 x 10-5 R-NH2 amines Brønsted-Lowry Acids and Bases .. acid proton donor H base proton acceptor .. + .. .. H Cl + H O Cl- + H O H H H conjugate pair base acid strong acid very weak base conjugate pair stronger acid + stronger base Brønsted-Lowry Acids and Bases strength of acid related to stability of conjugate base conjugate bases carry negative charges stabilized by: polarizability related to size (LDF) electronegativity inductive effect e- in resonance HI H+ + IHBr H+ + BrHCl H+ + ClHF H+ + F- 5p orbital 4p orbital 3p orbital 2p orbital largest orbital most stable strongest acid 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 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 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 Brønsted-Lowry Acids and Bases acid proton donor base proton acceptor H acid base weak base - .. .. .. .. .. + H N H +H O H N H + H O .. H H H base acid relatively strong acid Kb = 1.8 x 10-5 Autoionization of H2O H2O H+ (aq) + OH- (aq) H > 0 Kw = [H+] [OH-] = 1.0 x 10-14 at 25oC +] =O] -] 55.5 -7 M [H[H [OH = 1.0 x 10 2 0.0000001 Kw = [0.1] [OH-] =-1.0 x 10-14 [OH-] = 1.0 x 10-13 -] decrease + Le Chatelier [OH add H 0.10 mol HCl = 0.1 mol H+ [H+] = 0.10 M 1.0 L L both present in all aqueous solutions pH [H+] 10 M - 10-15 M low pH -1 acidic pH = - log [H+] 15 high pH basic neutral [H+] = [OH-] = 1.0 x 10-7 pH = 7 pH + pOH = 14 pOH = - log [OH-] pH of milk = 6.4 [H+] = 3.981071706 x 10-7 10 -6.4 4 x 10-7 1 sig. fig. Brønsted-Lowry Acids and Bases acid proton donor base proton acceptor C2H3OOH + CN- C2H3OO- + HCN base1 acid2 acid1 base 2 Brønsted-Lowry Acids and Bases acid proton donor base proton acceptor HF + H2O + acid1 base2 base1 acid2 F- H3O+ Ka = 7.2 x 10-4 CH3NH2 + H2O CH3NH3+ + OHbase1 acid2 acid1 base2 H3O+ strongest acid in water OH- strongest base in water H2O amphoteric acid or base