The document discusses key concepts in chemistry including: 1. Buffered solutions resist changes in pH when acids or bases are added due to the presence of a weak acid and its conjugate base. 2. The Henderson-Hasselbalch equation relates the pH of a buffer to the concentration ratio of its conjugate base and acid. 3. Buffers contain relatively large amounts of a weak acid and its conjugate base, allowing added H+ or OH- ions to react without significantly changing the pH.

1. Common Ion Effect
Copyright©2000 by Houghton 1 Mifflin Co mpany. The shift in equilibrium that occurs because
of the addition of an ion already involved in
the equilibrium reaction.
AgCl(s) « Ag+(aq) + Cl-(aq)
adding NaCl(aq) shifts equilibrium position ¬¾¾¾¾¾¾¾¾¾¾¾¾

2. A Buffered Solution
Copyright©2000 by Houghton 2 Mifflin Co mpany. . . . resists change in its pH when either H+ or
OH- are added.
1.0 L of 0.50 M H3CCOOH
+ 0.50 M H3CCOONa
pH = 4.74
Adding 0.010 mol solid NaOH raises the pH
of the solution to 4.76, a very minor change.

3. Key Points on Buffered Solutions
Copyright©2000 by Houghton 3 Mifflin Co mpany. 1. They are weak acids or bases containing
a common ion.
2. After addition of strong acid or base,
deal with stoichiometry first, then
equilibrium.

4. Henderson-Hasselbalch Equation
Useful for calculating pH when the
[A-]/[HA] ratios are known.
pH = p K a
+ log( A -
/ HA
)
=
p K
a
+
log( base / acid
)
Copyright©2000 by Houghton 4 Mifflin Co mpany.

5. Buffered Solution Characteristics
Copyright©2000 by Houghton 5 Mifflin Co mpany. Buffers contain relatively large amounts of weak
acid and corresponding base.
Added H+ reacts to completion with the weak
base.
Added OH- reacts to completion with the weak
acid.
The pH is determined by the ratio of the
concentrations of the weak acid and weak base.

6. Buffering Capacity
Copyright©2000 by Houghton 6 Mifflin Co mpany. . . . represents the amount of H+
or OH- the buffer can absorb
without a significant change
in pH.

7. Titration (pH) Curve
Copyright©2000 by Houghton 7 Mifflin Co mpany. A plot of pH of the solution being
analyzed as a function of the amount of
titrant added.
Equivalence (stoichiometric) point:
Enough titrant has been added to react
exactly with the solution being
analyzed.

8. Weak Acid - Strong Base
Titration
Copyright©2000 by Houghton 8 Mifflin Co mpany. Step 1 - A stoichiometry problem - reaction is
assumed to run to completion - then
determine remaining species.
Step 2 - An equilibrium problem - determine
position of weak acid equilibrium and
calculate pH.

9. Acid-Base Indicator
Copyright©2000 by Houghton 9 Mifflin Co mpany. . . . marks the end point of a titration by
changing color.
The equivalence point is not necessarily the
same as the end point.

10. Solubility Product
Copyright©2000 by Houghton 10 Mifflin Co mpany. For solids dissolving to form aqueous
solutions.
Bi2S3(s) « 2Bi3+(aq) + 3S2-(aq)
Ksp = solubility product constant
and
Ksp = [Bi3+]2[S2-]3

11. Solubility Product
Copyright©2000 by Houghton 11 Mifflin Co mpany. “Solubility” = s = concentration of
Bi2S3 that dissolves, which equals
1/2[Bi3+] and 1/3[S2-].
Note: Ksp is constant (at a given
temperature)
s is variable (especially with a common
ion present)

12. Equilibria Involving Complex
Ions
Complex Ion: A charged species consisting
of a metal ion surrounded by ligands (Lewis
bases).
Coordination Number: Number of ligands
attached to a metal ion. (Most common are 6
and 4.)
Formation (Stability) Constants: The
equilibrium constants characterizing the
stepwise addition of ligands to metal ions.
Copyright©2000 by Houghton 12 Mifflin Co mpany.