A.P. Chemistry Chapter 17 Outline: Buffers and Ksp
I.
Buffer Solutions: solutions that resist changes in pH when limited amounts of
acid or base are added to it
A. Buffering Action
1. A buffer must contain a weak acid that can react with the added base and
a weak base that can react with the added acid
2. Buffers usually consist of approximately equal quantities of a weak acid
and its conjugate base, or a weak base and its conjugate acid.
B. The pH of Buffer Solutions
1. Can be calculated by using H3O+ in the Ka expression
2. The Henderson-Hasselbach Equation an be used to calculate pH and also
to determine the ratio of conjugate base to conjugate acid concentrations
needed to achieve buffers of a given pH
Ph = pka + log [conjugate base/conjugate acid]
This equation has two limitations: The ratio must be between 0.1 and 10, and
the concentrations of both conjugates must exceed their ka values by a factor
of at leas a 100.
3. A buffers pH equals the pka of its weak acid when the concentrations of
the acid and base are equal
4. The ph range of a buffer is limited to about one pH unit above or below
the pka of the conjugate acid
C. Buffer Capacity: the quantity of acid or base the buffer can accommodate
without undergoing significant pH changes
II.
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III.
Acid-Base Titrations
A standard solution, one whose concentrations is known accurately, is added
from a buret to an acid or base which concentration is to be determined. The
solution in the buret is known as the titrant and the equivalence point is
reached when stoichiometric amounts of titrant have been added to neutralize
the unknown. The end point of a titration occurs when the indicator turns
color.
Titration curves are graphs of pH as a function of the volume of the titrant
added.
Titrations of a Polyprotic Acid with Base: polyprotic acids react stepwise
when titrated with bases
Acid Rain: the reaction of water with carbon dioxide, nitrogen dioxide, and
sulfur oxides
IV. Solubility Equilibria and the Solubility Product, ksp
 An equilibrium expression can be written to indicate the extent to which a
solid solute dissolves to form ions
 The solubility is the amount of solute per unit volume of solution (mol/L)
that dissolves to form a saturated solution.

The solubility product constant is the equilibrium constant for the
chemical equilibrium that exists between a solid ionic solute and its ions in
a saturated solution.
2.
3.
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5.
VI.
Factors Affecting Solubility
The effect of acids and pH
The presence of common ions
the formation of complex ions
amphoterism
VII. Will Precipitation Occur
 precipitation may nor occur if the concentrations are less than 0.1M
 if Q<ksp no ppt
 if Q>ksp ppt forms
 if Q=ksp the solution is saturated and is at equilibrium and at the point of
precipitation