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Ab Lec1

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Ab Lec1

  1. 1. ACIDS & BASES  DEFINITIONS 1. Operational 2. Conceptual a. Arrhenius b. Bronsted-Lowry c. Lewis  AMPHOTERISM 1. water and ammonia 8/19/2006 2. polyprotic acids /rmbb 1
  2. 2. OPERATIONAL DEFINITION based on experimental data - These are definitions using our senses with the help of colorimetric instruments such as indicators (litmus, phenolphthalein, methyl orange, etc.). ACIDS BASES • Electrolytes* • Electrolytes* • Taste sour • With bitter taste • Turn blue litmus • Feel slippery red • Turn red litmus blue • React with metal to • Pink  violet with form H2 gas phph • Colorless with phph • Yellow with methyl ectrolytes can bemethyl • Red with classified as weak or strong depending 2on it orange /rmbb
  3. 3. /rmbb 3
  4. 4. /rmbb 4
  5. 5. 8/19/2006 /rmbb 5
  6. 6. CONCEPTUAL DEFINITION - These are definitions of acids and bases based on theories proposed by different scientists namely: Acid Base - yields - yields Arrhenius hydrogen ion (H+) hydroxide ion in aq’s solution (OH-) in aq’s solution - proton Bronsted & Lowry - proton donor acceptor Lewis - e- pair acceptor - e- pair donor /rmbb 6
  7. 7. Limitations of each definition: • H+ vs. H3O+ • inability of compounds without OH_ to be a base • hydrogen containing compounds that cannot donate H+ • inability of compounds without H+ to be an acid Example s: /rmbb 7
  8. 8. Examples of Arrhenius acids & bases 1) HCl → H+(aq) + Cl-(aq) 2) NaOH → Na+(aq) + OH-(aq) 3) CH3COOH → CH3COO-(aq) + H+(aq) 4) H2SO4 → H+(aq) + HSO4-(aq) 5) Ba(OH)2 → Ba2+(aq) + 2 OH-(aq) 6) KOH → K+(aq) + OH-(aq) 7) NaCl → Na+(aq) + Cl-(aq) /rmbb 8
  9. 9. Conjugate Acids & Bases  A conjugate pair is composed of one acid and one base. 1 2 1 2 Examples of Bronsted-Lowry acids & bases 8/19/2006 /rmbb 9
  10. 10. /rmbb 10
  11. 11. Relative Strengths of Bronsted-Lowry Acids & Bases According to this theory, the strength of an acid is measured by its tendency to donate a proton, while that of a base is measured by its tendency to accept a proton. RULE 1: The stronger an acid is, the weaker its conjugate base. The stronger the base is, the weaker its conjugate acid. RULE 2: Proton transfer reactions tend to favor the formation of the weaker acid and the weaker base. /rmbb 11
  12. 12. A. Complete and identify the conjugate acid-base pairs in the following reactions: 1. NH3 + HF ⇔  CN- + H2O ⇔ B. Complete the following acid-base reactions & predict the direction of the predominant proton transfer reaction and show it by the lengths of the arrows.:  HCl + H2O →  CH3COOH + H2O → /rmbb 12
  13. 13. Examples of Lewis acids & bases 1.Electron-deficient molecules 2.Cations 3.Super-octet molecules 4.Molecules with multiple bonds /rmbb 13

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