1. Chemistry Notes Acid/Base Theories

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

3. 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. There are three ways to describe an acid: Monoprotic-gives off one H + in solution 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 Bronsted and Thomas Lowry proposed a new idea.

6. 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. NH 3 + H 2 O  NH 4 + + OH - Which is the initial acid? Which is the initial base? What is the conjugate acid? What is the conjugate base?

10. NH 3 + H 2 O  NH 4 + + OH - Which is the initial acid? H 2 O Which is the initial base? What is the conjugate acid? What is the conjugate base?

11. NH 3 + H 2 O  NH 4 + + OH - Which is the initial acid? H 2 O Which is the initial base? NH 3 What is the conjugate acid? What is the conjugate base?

12. NH 3 + H 2 O  NH 4 + + OH - Which is the initial acid? H 2 O Which is the initial base? NH 3 What is the conjugate acid? NH 4 + What is the conjugate base?

13. NH 3 + H 2 O  NH 4 + + OH - Which is the initial acid? H 2 O Which is the initial base? NH 3 What is the conjugate acid? NH 4 + What is the conjugate base? OH -

14. HCl + H 2 O  H 3 O + + Cl - Which is the initial acid? Which is the initial base? What is the conjugate acid? What is the conjugate base?

15. HCl + H 2 O  H 3 O + + Cl - Which is the initial acid? HCl Which is the initial base? What is the conjugate acid? What is the conjugate base?

16. HCl + H 2 O  H 3 O + + Cl - Which is the initial acid? HCl Which is the initial base? H 2 O What is the conjugate acid? What is the conjugate base?

17. HCl + H 2 O  H 3 O + + Cl - Which is the initial acid? HCl Which is the initial base? H 2 O What is the conjugate acid? H 3 O + What is the conjugate base?

18. HCl + H 2 O  H 3 O + + Cl - Which is the initial acid? HCl Which is the initial base? H 2 O What is the conjugate acid? H 3 O + What is the conjugate base? Cl -

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