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Acid-Base Chapter notes

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20sec3 Presentation Transcript

  • 1. 20.3 Acid, Base Theories
  • 2. Svante Arrhenius
    • Swedish chemist (1859-1927) - Nobel prize winner in chemistry (1903)
    • one of the first chemists to explain the chemical theory of the behavior of acids and bases
    • Dr. Hubert Alyea-last graduate student of Arrhenius.
  • 3. Hubert N. Alyea (1903-1996)
  • 4. 1. Arrhenius Definition - 1887
    • Acids produce hydrogen ions (H 1+ ) in aqueous solution.
    • Bases produce hydroxide ions (OH 1- ) when dissolved in water.
    • Limited to aqueous solutions.
    • Only one kind of base (hydroxides)
    • NH 3 (ammonia) could not be an Arrhenius base.
  • 5. Svante Arrhenius (1859-1927)
  • 6. Polyprotic Acids
    • Some compounds have more than 1 ionizable hydrogen.
    • HNO 3 nitric acid - monoprotic
    • H 2 SO 4 sulfuric acid - diprotic - 2 H +
    • H 3 PO 4 phosphoric acid - triprotic - 3 H +
    • Having more than one ionizable hydrogen does not mean stronger!
  • 7. Polyprotic Acids
    • However, not all compounds that have hydrogen are acids
    • Also, not all the hydrogen in an acid may be released as ions
      • only those that have very polar bonds are ionizable - this is when the hydrogen is joined to a very electronegative element
  • 8. Arrhenius examples...
    • Consider HCl
    • What about CH 4 (methane)?
    • CH 3 COOH (ethanoic acid, also called acetic acid) - it has 4 hydrogens just like methane does…?
    • Table 20.4 pg 595 for bases
  • 9. Organic Acids Organic acids all contain the “carboxyl” group, (-COOH), sometimes several of them. CH 3 COOH – of the 4 hydrogen, one 1 ionizable The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.
  • 10. 2. Brønsted-Lowry - 1923
    • Broader definition than Arrhenius
    • Acid is hydrogen-ion donor (H + or proton); base is hydrogen-ion acceptor.
    • Acids and bases always come in pairs.
    • HCl is an acid.
      • When it dissolves in water, it gives it’s proton to water.
    • HCl(g) + H 2 O(l) H 3 O + + Cl -
    • Water is a base; makes hydronium ion.
  • 11. Johannes Bronsted Thomas Lowry (1879-1947) (1874-1936)
  • 12. Why Ammonia is a Base
    • Ammonia can be explained as a base by using Bronsted-Lowry:
    • NH 3(aq) + H 2 O (l) ↔ NH 4 1+ (aq) + OH 1- (aq)
    • Ammonia is the hydrogen ion acceptor ( base ), and water is the hydrogen ion donor ( acid ).
    • This causes the OH 1- concentration to be greater than in pure water, and the ammonia solution is basic
  • 13. Acids and bases come in pairs
    • A “ conjugate base” is the remainder of the original acid, after it donates it’s hydrogen ion
    • A “ conjugate acid” is the particle formed when the original base gains a hydrogen ion
    • Indicators are weak acids or bases that have a different color from their original acid and base
  • 14. Acids and bases come in pairs
    • General equation is:
    • HA(aq) + H 2 O(l) ↔ H 3 O + (aq) + A - (aq)
    • Acid + Base ↔ Conjugate acid + Conjugate base
    • NH 3 + H 2 O ↔ NH 4 1+ + OH 1-
    • base acid c.a. c.b.
    • HCl + H 2 O ↔ H 3 O 1+ + Cl 1-
    • acid base c.a. c.b.
    • Amphoteric – a substance that can act as both and acid and base- as water shows
  • 15. 3. Lewis Acids and Bases
    • Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a reaction
    • Lewis Acid - electron pair acceptor
    • Lewis Base - electron pair donor
    • Most general of all 3 definitions; acids don’t even need hydrogen!
    • Summary: Table 20.6 page 598
  • 16. Gilbert Lewis (1875-1946)
  • 17. - Page 593