1. Acids and Bases

2. Dissociation of Strong Bases  Strong bases are metallic hydroxides  Group I hydroxides (NaOH, KOH) are very soluble  Group II hydroxides (Ca, Ba, Mg, Sr) are less soluble  pH of strong bases is calculated directly from the concentration of the base in solution MOH(s)  M + (aq) + OH - (aq)

3. Reaction of Weak Bases with Water The base reacts with water, producing its conjugate acid and hydroxide ion: CH 3 NH 2 + H 2 O  CH 3 NH 3 + + OH - K b = 4.38 x 10 -4

4. K b for Some Common Weak Bases BaseFormula Conjugate Acid KbKb Ammonia NH 3 NH 4 + 1.8 x 10 -5 Methylamine CH 3 NH 2 CH 3 NH 3 + 4.38 x 10 -4 Ethylamine C 2 H 5 NH 2 C 2 H 5 NH 3 + 5.6 x 10 -4 Diethylamine (C 2 H 5 ) 2 NH (C 2 H 5 ) 2 NH 2 + 1.3 x 10 -3 Triethylamine (C 2 H 5 ) 3 N (C 2 H 5 ) 3 NH + 4.0 x 10 -4 Hydroxylamine HONH 2 HONH 3 + 1.1 x 10 -8 HydrazineH 2 NNH 2 H 2 NNH 3 + 3.0 x 10 -6 Aniline C 6 H 5 NH 2 C 6 H 5 NH 3 + 3.8 x 10 -10 Pyridine C 5 H 5 N C 5 H 5 NH + 1.7 x 10 -9 Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?

5. Reaction of Weak Bases with Water The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion: B + H 2 O  BH + + OH - (Yes, all weak bases do this – DO NOT endeavor to make this complicated!)

6. A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? Step #1: Write the equation for the reaction NH 3 + H 2 O  NH 4 + + OH -

7. A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? Step #2: ICE it! I C E 0.50 0 0 - x +x 0.50 - x xx NH 3 + H 2 O  NH 4 + + OH -

8. A Weak Base Equilibrium Problem Step #3: Set up the law of mass action 0.50 - xxx E What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? NH 3 + H 2 O  NH 4 + + OH -

9. A Weak Base Equilibrium Problem Step #4: Solve for x, which is also [OH - ] 0.50 - xxx E [OH - ] = 3.0 x 10 -3 M NH 3 + H 2 O  NH 4 + + OH - What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ?

10. A Weak Base Equilibrium Problem Step #5: Convert [OH - ] to pH 0.50 - xxx E What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? NH 3 + H 2 O  NH 4 + + OH -

11. Read 14.6: Bases Page 706 questions #71,72,79,80,83,84