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Acid-Base Equilibrium

Acid-Base Equilibrium. Chapter 18. Acids and Bases. Arrhenius acids: generate H + in water bases: generate OH - in water Br ønsted-Lowry acids: H + donors bases: H + acceptors HCl + H 2 O  Cl  + H 3 O + acid base .

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Acid-Base Equilibrium

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  1. Acid-Base Equilibrium Chapter 18

  2. Acids and Bases • Arrhenius • acids: generate H+ in water • bases: generate OH- in water • Brønsted-Lowry • acids: H+ donors • bases: H+ acceptors • HCl + H2O  Cl + H3O+ • acid base

  3. H3O+ = H+(aq) = proton in water

  4. Acid + Base Base + Acid Conjugate acid-base pairs • Conjugate base: • remains after H+ is lost • acid: HCl conj. base: Cl- • Conjugate acid: • remains after H+ is gained • base: NH3 conj. acid: NH4+ Conjugate Pair Conjugate Pair

  5. Strong and Weak Acids • Strong:100% dissociation • good H+ donor • equilibrium lies far to right (HNO3) • generates weak base (NO3-) • Weak:<100% dissociation • not-as-good H+ donor • equilibrium lies far to left (CH3COOH) • generates strong base (CH3COO-)

  6. Relative Acid Strength Relative Conj. Base Strength Very strong Very weak Strong Weak Weak Strong Very weak Very strong

  7. Acid Dissociation Constant

  8. Strength vs. Ka Ka Increases

  9. Water is amphoteric • Acid Base Conj. Acid Conj. Base

  10. H H H H O H O H O H O H H H H H O H O H H O O H - + H H H H - O O H O H O H H Proton Transfer in Water

  11. [H3O+] and [OH-] • [H3O+] 1x100 to 1x10-14 in water • [OH-] 1x10-14 to 1x100 in water

  12. Finding [H3O+] and [OH-]

  13. pH Scale • pH 0 to 14 in water • pOH 14 to 0 in water • pKw = pH + pOH = 14

  14. OH- OH- OH- H+ H+ H+ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Neutral Basic pH and pOH • As [H3O+] rises, [OH-] falls • As pH falls, pOH rises

  15. Indicators

  16. Polyprotic Acids 1. H3PO4H2PO4- + H+ • Ka1 = 7.2 x 10-3 • 2. H2PO4-HPO42-+ H+ • Ka2 = 6.3 x 10-8 • 3. HPO42-PO43-+ H+ • Ka3 = 4.2 x 10-13 Ka1 > Ka2 > Ka3

  17. Strength of Bases • Strong: • 100% dissociation • OH- supplied to solution • NaOH(s) Na+(aq) + OH-(aq) • Weak: • <100% dissociation • OH- by reaction with water CH3NH2(aq) + H2O(l) CH3NH2(aq)+ OH-(aq)

  18. Base Dissociation Constant

  19. Kw, Ka and Kb

  20. Structure and Acid-Base Behavior • Binary hydrides: • 1. Bond polarity (high  acid strength) • 2. Bond strength (low  acid strength)

  21. Structure and Acid-Base Behavior • Binary oxides: • 1. Acidic oxides (acid anhydrides) • O—X bond: strong and polar • SO2, SO3, NO2, P4O10, … • 2. Basic oxides (basic anhydrides) • O—X bond: ionic • K2O, CaO, …

  22. Structure and Acid-Base Behavior • Oxoacids (HaXbOc): • 1. Same number of O on different X • EN of X • 2. Different number of O on same X • more O

  23. Relative Strengths of Oxoacids

  24. O H Cl 1 O Electron density O Cl O H 2 O Electron density O Cl O H O 3 O Electron density O O Cl O H 4 O O Electron density Increasing Acid Strength

  25. 3 + H H 3 + A l + 6 O A l O H H 6 Lewis Acids and Bases • Lewis Acid: electron pair acceptor • Lewis Base: electron pair donor Acid Base

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