CH 16_student_6_per_page_sp07

CH 16_student_6_per_page_sp07 - Contents 16-1 16-2 16-3...

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Unformatted text preview: Contents 16-1 16-2 16-3 16-4 16-5 16-8 The Arrhenius Theory: A Brief Review Brønsted-Lowry Theory of Acids and Bases The Self-Ionization of Water and the pH Scale Strong Acids and Strong Bases Weak Acids and Weak Bases Lewis Acids and Bases Chapter 16: Acids and Bases Dr. Berk & Dr. Koel CHM 25 Spring 2007 Slide 1 of 48 CHM 25 SP07 Slide 2 of 48 CHM 25 SP07 The Arrhenius Theory: A Brief Review HCl(g) NaOH(s) H2O Brønsted-Lowry Theory of Acids and Bases ♦ An acid is a proton donor. ♦ A base is a proton acceptor. id se e ac e ba ugat njugat c on j co H+(aq) + Cl-(aq) Na+(aq) + OH-(aq) H2O(l) + Na+(aq) + Cl-(aq) H2O(l) OHCHM 25 SP07 H2O Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) H+(aq) + OH-(aq) base acid NH3 + H2O NH4+ + OHacid base NH4+ + OHNH3 + H2O ?? ?? Arrhenius theory did not handle non bases such as ammonia very well. Slide 3 of 48 Slide 4 of 48 CHM 25 SP07 Acid Ionization Constant acid base conjugate base conjugate acid CH3CO2H + H2O Kc= CH3CO2- + H3O+ [CH3CO2-][H3O+] [CH3CO2H][H2O] [CH3CO2-][H3O+] = 1.8×10-5 [CH3CO2H] Ka= Kc[H2O] = Slide 5 of 48 CHM 25 SP07 Slide 6 of 48 CHM 25 SP07 CHM 25 SP07 1 Base Ionization Constant base acid conjugate conjugate base acid NH3 + H2O Kc= NH4+ + OH- [NH4+][OH-] [NH3][H2O] [NH4+][OH-] = 1.8×10-5 [NH3] Kb= Kc[H2O] = Slide 7 of 48 CHM 25 SP07 Slide 8 of 48 CHM 25 SP07 A Weak Base A Weak Acid Slide 9 of 48 CHM 25 SP07 Slide 10 of 48 CHM 25 SP07 A Strong Acid In the equilibrium system described by: PO43- (aq) + H2O(1) HPO42 -(aq) +OH-(aq) Brønsted-Lowry theory would designate: 1. PO43- and H2O as the bases 2. H2O and OH- as a conjugate pair 3. HPO42- and OH- as the acids 0% 0% 0% 4. HPO42- and H2O as a conjugate pair 0% Slide 11 of 48 CHM 25 SP07 Slide 12 of 48 CHM 25 SP07 CHM 25 SP07 2 The Self-Ionization of Water and the pH Scale Ion Product of Water base acid conjugate conjugate base acid H2O + H2O H3O+ + OH- Kc= [H3O+][OH-] [H2O][H2O] KW= Kc[H2O][H2O] = [H3O+][OH-] = 1.0×10-14 Slide 13 of 48 CHM 25 SP07 Slide 14 of 48 CHM 25 SP07 pH and pOH ♦ The potential of the hydrogen ion was defined in 1909 as the negative of the logarithm of [H+]. pH = -log[H3O+] pOH = -log[OH-] pH and pOH Scales KW = [H3O+][OH-]= 1.0×10-14 -logKW = -log[H3O+]-log[OH-]= -log(1.0×10-14) pKW = pH + pOH= -(-14) pKW = pH + pOH = 14 Slide 15 of 48 CHM 25 SP07 Slide 16 of 48 CHM 25 SP07 You add 0.0010 mol of NaOH to 1.0 L of NaOH to pure water. Calculate [H3O+] and [OH-]. pure Solution 2 H2O(liq) H3O+(aq) + OH-(aq) O(liq) Le Chatelier predicts equilibrium shifts to Le Chatelier predicts the ____________. [H3O+] < 10-7 at equilibrium. [H Set up a ICE table. Slide 17 of 48 CHM 25 SP07 2 H2O(liq) H3O+(aq) + OH-(aq) O(liq) initial 0 0.0010 change +x +x equilib x 0.0010 + x Kw = (x) (0.0010 + x) Because x << 0.0010 M, assume Because [OH-] = 0.0010 M [OH +] = K / 0.0010 = 1.0 x 10-11 M [H3O w Slide 18 of 48 You add 0.0010 mol of NaOH to 1.0 L of NaOH to pure water. Calculate [H3O+] and [OH-]. pure Solution CHM 25 SP07 CHM 25 SP07 3 You add 0.0010 mol of NaOH to 1.0 L of pure water. NaOH to Calculate [H3O+] and [OH-]. Calculate Solution 2 H2O(liq) H3O+(aq) + OH-(aq) O(liq) [H3O+] = Kw / 0.0010 = 1.0 x 10-11 M This solution is _________ because [H3O+] Slide 19 of 48 If the pH of Coke is 3.12, it is ____________. If Because pH = - log [H3O+] then Because log [H3O+] = - pH Take antilog and get [H3O+] = 10-pH [H3O+] = 10-3.12 = 7.6 x 10-4 M 7.6 CHM 25 SP07 Slide 20 of 48 CHM 25 SP07 < [OH-] Strong Acids and Bases HCl CH3CO2H Weak Acids and Bases Acetic Acid Thymol Blue Indicator pH < 1.2 < pH < 2.8 < pH Lactic Acid Slide 22 of 48 Glycine CHM 25 SP07 Slide 21 of 48 CHM 25 SP07 ! "# $ % & ! "# Consider acetic acid, CH3CO2H (HOAc) Consider HOAc + H2O H3O+ + OAcOAc Acid Conj. base Ka = [H3 O+ ][OAc - ] = 1.8 x 10 -5 [HOAc] (K is designated Ka for ACID) for ACID Because [H3O+] and [OAc-] are SMALL, Ka << 1. Slide 23 of 48 CHM 25 SP07 Weak acid has Ka < 1 Weak Leads to small [H3O+] and a pH of 2 - 7 Leads and Slide 24 of 48 CHM 25 SP07 CHM 25 SP07 4 Weak Acids & Acetic Acid % ! "$ Ka= [CH3CO2-][H3O+] = 1.8×10-5 [CH3CO2H] Weak base has Kb < 1 Weak Leads to small [OH-] and a pH of 12 - 7 Leads and Slide 25 of 48 CHM 25 SP07 Slide 26 of 48 CHM 25 SP07 Weak Bases Table 16.3 Ionization Constants of Weak Acids and Bases Kb= [CH3NH3+][HO-] = 4.3×10-4 [CH3NH2] pKb= -log(4.2×10-4) = 3.37 Slide 27 of 48 CHM 25 SP07 Slide 28 of 48 CHM 25 SP07 ' & # ($ Increase strength ) &* * Increase strength Slide 29 of 48 CHM 25 SP07 Slide 30 of 48 CHM 25 SP07 CHM 25 SP07 5 * # $ ) * # $ ) ACIDS ACIDS STRONG STRONG weak weak CONJUGATE BASES CONJUGATE BASES weak weak STRONG STRONG A strong acid is 100% dissociated. strong Therefore, a + , ) - . # / —a good H+ Therefore, donor—must have a ! # * - 01 .# , must $ # + —a poor H+ acceptor. acceptor. HNO3(aq) + H2O(liq) H3O+(aq) + NO3-(aq) HNO O(liq) STRONG A base acid acid weak B weak •Every A-B reaction has two acids and two •Every A-B reaction has two acids and two bases. bases. bases. •Equilibrium always lies toward the weaker pair. •Equilibrium always lies toward the weaker pair. Slide 32 48 CHM 25 SP07 •HereofK is very large. •Here K is very large. Slide 31 of 48 CHM 25 SP07 * # BASE $ ) ACID * # $ ) HNO3 + H2O STRONG ACID H3O+ + NO3WEAK BASE We know from experiment that HNO3 is a We is strong acid. strong 1. It is a stronger acid than H3O+ 2. H2O is a stronger base than NO33. K for this reaction is large Slide 33 of 48 CHM 25 SP07 Slide 34 of 48 CHM 25 SP07 * # $ ) * # $ ) Acetic acid is only 0.42% ionized when [HOAc] = 1.0 M. It is a WEAK ACID HOAc WEAK A + H2O base H3O+ acid + OAcSTRONG B Because [H3O+] is small, this must mean 1.H3O+ is a stronger acid than HOAc 2.OAc- is a stronger base than H2O 3.K for this reaction is small Slide 35 of 48 CHM 25 SP07 Slide 36 of 48 CHM 25 SP07 CHM 25 SP07 6 * # $ ) Polyprotic Acids Phosphoric acid: A triprotic acid. H3PO4 + H2O H2PO4- + H2O HPO42- + H2O Slide 37 of 48 CHM 25 SP07 Slide 38 of 48 H3O+ + H2PO4H3O+ + HPO42H3O+ + PO43- Ka = 7.1×10-3 Ka = 6.3×10-8 Ka = 4.2×10-13 CHM 25 SP07 Polyprotic Acids - Bases Sulfuric acid: Diprotic Acids A diprotic acid. H2SO4 + H2O HSO4- + H2O H3O+ + HSO4H3O+ + SO42- Ka = very large Ka = 1.96 Slide 39 of 48 CHM 25 SP07 Slide 40 of 48 CHM 25 SP07 16-9 Lewis Acids and Bases ♦ Lewis Acid • A species (atom, ion or molecule) that is an electron pair acceptor. 23 # ($ ) ♦ Lewis Base • A species that is an electron pair donor. base Slide 41 of 48 acid adduct CHM 25 SP07 Slide 42 of 48 CHM 25 SP07 CHM 25 SP07 7 ! Other good examples involve metal ions. Co 2+ Showing Electron Movement • •• • O—H H BASE Co2+ • •• • O—H H ACID Slide 43 of 48 CHM 25 SP07 Slide 44 of 48 CHM 25 SP07 The concept of an acid not limited to H+ or species containing one or more protons is inherent in: 1. only the Arrhenius theory 2. both the Arrhenius and the Brønsted-Lowry theories 3. only the Brønsted-Lowry theory 4. both the Brønsted-Lowry and the Lewis theories 5. only the Lewis theory th e on ly ! The combination of metal ions (Lewis acids) with The Lewis bases such as H2O and NH3 Lewis ------> 4 25 -+ 0% 0% 0% 0% 0% Slide 45 of 48 bo th A rr he ni us Ar t. . . rh on en ly iu th s e an B rø . .. bo ns th te th de L. Br .. øn on st ed ly -L th .. . e Le w is th eo ry th e CHM 25 SP07 Slide 46 of 48 CHM 25 SP07 #% 6 % &# 7 8 ! This explains # 4 , This of some metal hydroxides. of ) nature Al(OH)3(s) + 3 H+ --> Al3+ + 3 H2O Here Al(OH)3 is a Brønsted base. is Br Al(OH)3(s) + OH- --> Al(OH)4Here Al(OH)3 is a Lewis acid. Al3+ •• O—H •• CHM 25 SP07 •• Slide 47 of 48 CHM 25 SP07 Slide 48 of 48 CHM 25 SP07 8 ...
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