Weak Bases

1
Weak Bases
2

• Many substances behave as weak bases in water
• React with water removing protons from the H2O
  thus forming OH- ions
• Weak Base H2O ? Conj. Acid OH-

3
Ammonia

• NH3 H2O ? NH4 OH-
• Kb NH4OH-
• NH3
• Kb base-dissociation constant

4
Example

• Calculate the concentration of OH- in a .15M
  solution of NH3.

5
Weak Bases

• Ammonia NH3 Kb 1.8 x 10-5
• Pyridine C5H5N Kb 1.7 x 10-9
• Hydroxylamine H2NOH Kb 1.1 x 10-8
• Methylamine NH2CH3 Kb 4.4 x 10-4
• Nicotine C10H14N2 Kb 7 x 10-7
• Hydrosulfide HS- Kb 1.8 x 10-7
• Carbonate CO32- Kb 1.8 x 10-4
• Hypochlorite ClO4- Kb 3.3 x 10-7

6
Example

• Calculate the pH of .010M solution of sodium
  hypochlorite, NaClO.