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Chapter 19 Notes: Part II

Chapter 19 Notes: Part II. Acid/Base Theories. There are three ways to define acids and bases. This reflects the fact that science is always revising itself. 1) Arrhenius Acids/Bases. An acid is a chemical that gives off hydrogen ions in solution.

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Chapter 19 Notes: Part II

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  1. Chapter 19 Notes: Part II Acid/Base Theories

  2. There are three ways to define acids and bases. • This reflects the fact that science is always revising itself.

  3. 1) Arrhenius Acids/Bases • An acid is a chemical that gives off hydrogen ions in solution. • A base is a chemical that gives off hydroxide ions in solution. Example: HCl + NaOH NaCl + H2O **BASICALLY…acids start with H+ and bases end with OH-!!!

  4. Arrhenius Acids/Bases There are three ways to describe an acid: • Monoprotic-gives off one H+ in sol’n • Diprotic-gives off two H+ • Triprotic-gives off three H+

  5. Bronsted-Lowry Acids/Bases • The Arrhenius definition is a good one, but does not encompass everything that shows acidic/basic qualities. • To account for this, Johannes Bronstedand Thomas Lowryproposed a new idea.

  6. 2) Bronsted-Lowry Acids/Bases • An acid is a hydrogen-ion (proton) donor. • A base is a hydrogen-ion (proton) acceptor.

  7. Conjugate Acids/Bases • A conjugate acid is the particle that is formed when a base gains a hydrogen ion. • A conjugate base is the particle that is formed when an acid donates a hydrogen ion.

  8. Conjugate Acids/Bases • A conjugate acid/base pair consist of two substances related by the loss of a single hydrogen ion.

  9. NH3 + H2O  NH4+ + OH- proton donator • Which is the initial acid? • Which is the initial base? • What is the conjugate acid? • What is the conjugate base? H2O NH3 NH4+ OH- proton acceptor formed after base gains H+ formed after acid donates H+

  10. HCl + H2O  H3O+ + Cl- • Which is the initial acid? • Which is the initial base? • What is the conjugate acid? • What is the conjugate base? HCl H2O H3O+ Cl-

  11. Amphoteric Substances • Note that in one of the previous examples H2O was acidic and basic in the other. • A substance that can act as an acid or a base is called amphoteric.

  12. 3) Lewis Acids/Bases • A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. • A Lewis base is a substance that can donate a pair of electrons to a covalent bond.

  13. 3 7 5 1 H x x N x x H x F B F x x x x H N H x x x x x x x x x x x H x F x x H x x x x x x F B x x F x x x x x x x x x x x F x x x x x x **MUST draw Lewis dot structures to determine whether a compound will gain or lose e-!!! • Ex… BF3 + NH3 F3BNH3 ACID (not happy) accept e- pair BASE (happy) donate e- pair

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