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CH. 16 ACID -- BASE

16.4 pH scale (pOH). CH. 16 ACID -- BASE. 16.1 Definition. 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect. 16.3 Dissociation of water K w. 16.5 Strong Acid Strong Base pH & [ ]. 16.6 Weak Acids K a & pH % Ionization Polyprotic Acids. 16.7 Weak Bases

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CH. 16 ACID -- BASE

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  1. 16.4 pH scale (pOH) CH. 16 ACID -- BASE 16.1 Definition 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect 16.3 Dissociation of water Kw 16.5 Strong Acid StrongBase pH & [ ] 16.6 Weak Acids Ka & pH % Ionization Polyprotic Acids 16.7 Weak Bases Kb & pH Acid Base Yields 16.9 Salt Solutions Anions/Cations Lewis 16.8 Ka & Kb Relation 16.10 Binary Acids Oxyacids Carboxylic Acids 16.11 Bronstad-Lowry

  2. ACID BASE CHEMISTRY TERMS, ETC. AMPHOTERIC: Subst. acts as either an acid or a base H+ ion; the acidic hydrogen(s) present in an acid Proton (Acidic p+): H2SO4: two H+ HNO3: one H+ H3PO4: three H+ MONOPROTIC ACID: An acid w/ one H+ DIPROTIC ACID: An acid w/ two H+ POLYPROTIC ACID: An acid w/ 3 or more H+

  3. TERMS, ETC. ACID: Subst. in H2O incr [H+] BASE: Subst. in H2O incr [OH-] Effects H+ Ion in H2O HYDRONIUM ION: H2O (l) + H+1 (aq) ---------> H3O+1(aq)

  4. BRONSTAD-LOWRY ACID: Subst. that donate acidic proton, H+ Proton donor HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq) BASE: Subst. that gains acidic proton, H+ Proton acceptor

  5. CONJUGATE ACID-BASE PAIRS Acid, loses H+, form conjugate base Base, gains H+, forms conjugate acid base2 base1 acid1 acid2 CONJUGATE ACID-BASE PAIRS

  6. Fig 16.3 pg. 657

  7. RELATIVE STRENGTH HX(aq) + H2O(l) ----> H3O+(aq) + X-(aq) H2O stronger base than X- X weaker base --- equilib + acid ion of weak acid react w/ H2O, produces H3O+ Strong Acid + Weak Base --- Acidic HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq) H2O stronger base than Cl-

  8. X- stronger base than H2O X stronger base <---- equilib Weak Acid + Strong Base --- Basic CH3COOH(aq) + H2O(l) ----> H3O+(aq) + CH3COO-(aq) CH3COO- stronger base than H2O Proton Transfer: ability of 2 bases attract protons

  9. AUTOIONIZATION OF WATER Kc[H2O]2 = Kw = [H3O+][OH-] = 1.0*10-14 Solution Acid [H3O+] > [OH-] Neutral [H3O+] = [OH-] Basic [OH-] > [H3O+]

  10. pH SCALE 0 7 14 NEUTRAL ( ) MILD ACIDIC MILD BASIC WEAK ACIDIC WEAK BASIC STRONG ACIDIC STRONG BASIC Kw = [H+][OH-] 1*10-14 = [H+][OH-] Kw: constant for water, 1*10-14 pKw = -Log [H2O] = -Log [1*10-14] = -Log [10-14] -Log [1] = -(-14) - 0 = 14 pKw = pH + pOH pH = -Log [H+] pOH = -Log [OH-] [OH-] = 1*10-pOH [H+] = 1*10-pH Log 10exp = exp log 106 = 6 Log 10-4 = -4 Log 1 = 0

  11. Fig. 16.5 pg 663

  12. Formulas to Use Constants pH -- pOH -- [H+] -- [OH-] CALCULATIONS Kw = 1 *10 –14 pKw = 14 pH = -log [H+] pOH = -log [OH-] Rules for LOGS [H+] = 1*10-pH Log 1 = 0 [OH-] = 1*10-pOH Log 10exp = exponent

  13. Rules for LOGS Log 1 = 0 Log 103.17 = 3.17 Log 10exp = exponent

  14. Calculate pH for the following solutions 1) [H+] = 1 * 10-9 pH = -log (1*10-9) = -(-9) = 9 2) [H+] = 0.001 0.001 = 1*10-3 pH = -log (1*10-3) = -(-3) = 3

  15. Find pH & pOH 3) [H+] = 3.6 * 10-2 pH = -log(3.6*10-2) = 1.44 pH = 2 – log (3.6) = 2 – 0.56 = 1.44 -log 10-2 = 2 OR pKw = pH + pOH 14 = 1.44 + pOH pOH = 14 – 1.44 = 12.56 pOH OR = 2.78*10-13 pOH = 13 – log 2.78 = 13 – 0.44 =

  16. 1*10-14 [OH-] = 6.7*10-9 If [H+] is 6.7*10-9 mol/L, what is the pH? ACIDIC, BASIC, NEUTRAL What is the [OH-]? What is the pOH? Find pH Find pOH pH = -log(6.7*10-9) = 9 – log 6.7 = 9 – 0.83 = 8.17 pOH = 14 – 8.17 = 5.83 Find [OH-] BASIC [OH-] = 1*10-5.83 OR = 1.49*10-6

  17. TITRATIONS Strong Acid + Strong Base ------ Neutral +/- ions of acid not react w/ H2O Strong Acid + Weak Base --- Acidic + acid ion weak acid react w/ H2O, produces H3O+ HBr + NH4OH NH4 is a weak acid reacts w/ H2O to produce H3O+ Weak Acid + Strong Base --- Basic • acid ion weak base produces OH- • HCN: CN- is weak base reacts w/ H2O to produce OH- Weak Acid + Weak Base ---- ??????? Both +/- ions react w/ H2O

  18. DISSOCIATION HA: acid A-: anion Ka: acid-dissociation constant Strong Acid -- SA HA(aq) + H2O(l) --------> H3O+(aq) + A-(aq) SA in solution; no HA present, most all H3O+ @ equilibrium Qc = Kc >>>> 1 Weak Acid -- WA HCN(aq) + H2O(l) --------> H3O+(aq) + CN-(aq) WA in solution; no H3O+ present, most all HA @ equilibrium Qc = Kc <<<< 1 Stronger Acid ==> higher [H3O+] ===> larger Ka Smaller Ka ==> less % dissed ====> weaker acid

  19. IONIZATION CONSTANTS STRENGTH Strong Acid/Base ionize completely equilibrium lies far to the right HCl ------> H+ + Cl- NaOH -----> Na+ + OH- Weak Acid slightly ionize equilibrium lies far to the left HC2H3O2 + H2O <-----> H+ + C2H3O2- Ka: acid dissociation constant Kb: base dissociation constant

  20. Increasing acid strength Ka Values MONOPROTIC ACIDS Acid Ka Chlorous HClO4 Nitrous HNO2 Hydrofluoric HF Formic HCOOH Acetic CH3COOH Propanoic CH3CH2COOH Hypochlorous HClO Hydrocyanic HCN 1.1*10-2 7.1*10-4 6.8*10-4 1.8*10-4 1.8*10-5 1.3*10-5 2.9*10-8 6.2*10-10

  21. Problem Solving A-B Equilibria Steps 1. Write eqn & Ka/b expression 2. I.C.E. table 3. Define “x” as ; HA 4. Assume “x” very small 5. 5% rule 2 Assumptions 1. [H3O+] from water ignore 2. WA diss little, no  in concen Ka * Kb = Kw

  22. Ka = 6.8*10-4 for 0.75 M hydrofluoric acid solution is. Determine the concentrations of H3O+, A-, & OH-. Also, find the pH, pOH, & % acid dissociation. 1st write eqn & Ka 2nd construct table 3rd determine “change, x” [H3O+] = [F-] Kw = [H3O+] [OH-] 4th assume x negligible; 0.75 - x => 0.75

  23. pH = -Log(0.0223) = 1.65 pOH = 14 - 1.65 = 12.35 OR = -Log(4.4*10-13) = 12.36 % Diss = 0.0223/0.75 * 100 = 3.0 %

  24. HA % Dissociation The initial concen of an acid is 3.2*10-2 then at equilibrium the concen is now 6.4*10-5 What is the % diss? HA% = [HA]diss/[HA]init * 100 HA% = [2.8*10-4]/[1.2*10-2]* 100 = 2.3 %

  25. Classify Acid - Base Strengths WA Halogen acid: HF H not bonded to O: HCN, H2S, H3P Oxo acids: when # O’s < 2 H+ HNO2, HClO2, H3PO3 Carboxylic Acids: - COOH SA Halogen acids: HCl, HBr, HI Oxo acids: when # O’s > 1 H+ HNO3, HClO4, H2SO4 SB Contain O-2 or OH- Group 1A active metals: MOH, M2O Li, Na, K, Rb, Cs Group 2A active metals: M(OH)2, MO Ca, Sr, Ba WB Cmpds w/ e--rich N atom NH3, amines

  26. Ka acetic acid = 1.8*10-5 Ka nitrous acid = 4.4*10-4 nitrous acid more ionized in soln BASE NH3 + H2O <---> NH4+ +OH- Kb ammonia = 1.8*10-5

  27. Increasing base strength Increasing acid strength S.A. yields weak conjugate base W.A. yields strong conj. base MONOPROTIC ACIDS Ka Acid Kb Conj. Base 8.3*10-13 SO4-2 8.3*10-13 ClO2- 1.4*10-11 F- 5.56*10-10 C2H3O2- 2.9*10-7 OCl- 1.8*10-5 NH3 1.2*10-2 HSO4- 1.2*10-2 HClO2 7.2*10-4 HF 1.8*10-5 HC2H3O2 3.5*10-8 HOCl 5.6*10-10 NH4+

  28. conj. base strength acid strength HCl Strong Cl- H2SO4 HSO4- HNO3 NO3- H3O+ H2O HSO4- Weak SO4-2 H2SO3 HSO3- H2PO4 H2PO4- HF F- CH3COOH CH3COO- H2CO3 HCO3- H2S HS- HSO3- SO3-2 H2PO4 HPO4-2 Weak HCN CN- NH4+ NH3 HCO3- CO3-2 HPO4-2 PO4-3 H2O OH- Strong

  29. RXN DIRECTION Direction of SA & SB to form WA & WB H2PO4- + NH3 <------> NH4+ + HPO4-2 H2PO4- SA than NH4+ HS- + H2O <------> H2S + OH- H2S SA than H2O Acid Base rxn goes dir: if HA reacts w/ base lower on list

  30. Diprotic & Triprotic Acids H2CO3: 2 acidic protons Ka values for each H+ Ka1 = 4.3*10-7 Ka2 = 5.6*10-11 typically weak polyprotic acid Ka1 > Ka2 > Ka3 means???? -each step of dissociation is successively weaker -loss of 2nd & 3rd proton occurs less readily Why???? should not be surprising think in terms of charges, +/- being attracted

  31. Property S.A. W.A. [H+] [HA]o Various Ways to Describe Acid Strength Ka value Ka is large Ka is small Position of dissociation equilibrium Far to left Far to right Equilibrium [H+] compared to [HA]o [H+]<<[HA]o A- much weaker base than H2O Strength of conj.base compared to H2O A- much stronger base than H2O

  32. Acid Strength Nonmetal Hydrides The stronger the acid the better it is at donating H+ 2 factors of Acid Strength -- depends how easily the H+ is lost 1) Bond Polarity More polarized bond, quicker H+ lost, greater acid strength 2) Bond Strength Larger “none H” atom is, weaker the bond, greater acid strength Metal Ion Acid Strength high charge density, small metal ions: Fe+3, Al+3, Cu+2, Pb+2, Zn+2, Ni+2

  33. PROPERTIES OF SALTS pH of salt soln: A-B properties of cation & anion 1. SA + SB ----> Neutral 2. SA + WB ----> Acidic 3. WA + SB ---> Basic 1. Cat- & An-ions not react w/ water to form H3O+ or OH- 2. Anion inert; Cation WA, form H3O+ 3. Cation inert; Anion WB, form OH-

  34. 4. WA + WB ----> ???? Both ions undergo proton transfer Ka cation > Kb anion: ACIDIC Kb anion > Ka cation: BASIC Ka cation = Kb anion: NEUTRAL

  35. Leveling Effect All Bronstad acids form H3O+ in water & bases OH- SA completely form H3O+ SB completely form OH- Lewis Acids - Bases Molecules w/ central atom < 8 val e- Polar molecules w/ dbl bond Metal ions dissolved in water ID Lewis A & B Cl- + BCl3 <----> BCl4- Cl- form coval bond to B; Cl- 4 e- pair BCl3 accepts e- pair, ACID

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