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Chapter 8

CHM 111 Chapter Notes - Chapter 8: Buffer Solution, Weak Base

Course Code
CHM 111
Acevedo Orlando

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Solutions of Acids or Bases Containing a Common Ion
A. Common ion: an ion that is produced when both the weak acid and the salt dissolve
B. Common ion effect: a shift in equilibrium position to the left that occurs because of the
addition of an ion already involved in the equilibrium reaction
Buffered Solutions
A. Buffered Solution: one that resists a change in pH when either hydroxide ions or protons
are added
a. Ex: human blood
B. May contain a weak acid and its salt or a weak base and its salt
C. Buffered solutions are simply solutions of weak acids or bases containing a common ion.
The pH calculations for buffered solutions require exactly the same procedures
previously introduced in Chapter 7.
D. When a strong acid or base is added to a buffered solution, it is best to deal with the
stoichiometry of the resulting reaction first. After the stoichiometric calculations are
completed, then consider the equilibrium calculations.
E. Buffering: How Does It Work?
a. The equilibrium concentration of H+ and thus pH are determined by the ratio
b. When OH- ions are added. HA is converted to A-, causing the ratio [HA]/[A-] to
decrease. However, if the amounts of HA and A- originally present are very large
compared with the amount of OH- added, the change in the [HA]/[A-] ratio is
c. The essence of buffering then is that [HA] and [A-] are large compared with the
amount of OH- added. Therefore, the ratio remains virtually constant.
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