1. Conjugate Acid-Base Pairs

2. Acid Dissociation + 1- HCl Cl Conjugate base Acid Conjugate pair H
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 280

3. Conjugate Acid-Base Pairs
conjugates
base
acid
HCl H2O H3O Cl-
acid
base
conjugates
HCl H2O H3O Cl-
acid base CA CB

4. Conjugate Acid-Base Pairs
conjugates
acid
base
NH H2O NH OH-
base
acid
conjugates
base acid CA CB
NH H2O NH OH-

5. Water is Amphoteric HCl + H2O H3O+ + Cl- NH3 + H2O NH41+ + OH-
Amphoteric or Amphiprotic substances:
Substances which can act as either proton donors (acids) or
proton acceptors (bases) depending on what substances are present.
HCl H2O H3O Cl-
acid base CA CB
base acid CA CB
NH H2O NH OH-

6. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- 1+ + +
H2O
H3O+
HSO4-
H2SO4
water
hydronium ion
hydrogen sulfate
ion
sulfuric acid 1- +
sulfate ion
SO42-
water
H2O
hydrogen sulfate
ion
HSO4-
hydroxide ion
OH- 2-

7. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- + 1+ +
sulfuric acid
H2SO4
water
H2O
H3O+
HSO4-
hydronium ion
hydrogen sulfate
ion
(HSO4- as a base)

8. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- +
sulfate ion
SO42-
water
H2O 2- 1- +
HSO4-
OH-
hydrogen sulfate
ion
hydroxide ion
(HSO4- as an acid)

9. Conjugate Acid-Base Pairs
conjugates
base2
acid2
HC2H3O H2O H3O C2H3O2OH-
acid1
base1
conjugates
acid base CA CB
HC2H3O H2O H3O C2H3O2OH-
The reaction proceeds in the direction such that the stronger acid
donates its proton to the stronger base.