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

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13 Jan 2017

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CHAPTER 8: APPLICATIONS OF AQUEOUS EQUILIBRIA

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

[HA]/A-]

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

small

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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Related Questions

Select the statement that best describes a buffer.

A)A buffer prevents the pH of a solution from changing when an acid or base is added.

B) A buffer causes acidic solutions to become alkaline, and alkaline solutions to become acidic.

C) Buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added A buffer stabilizes the pH of a solution by preventing acids or bases from dissociating.

D) Buffered solutions are always neutral, with a pH of 7.

plummoose540

1. A 0.100 M solution of the weak acid HB has a pH of 3.00. What are the [H+], [B-], and Ka for this acid?

2. A solid acid is dissolved in water. Half the solution is titrated to a phenolphthalein end point with NaOH solution. The neutralized and acid solutions are then mixed and the pH of the resulting solution is found to be 4.60. Find Ka of the solid acid.

3. Assuming your buffered solution contains acetic acid, HOAc, and the sodium salt of its conjugate base, NaOAc. Show the net ionic equations that occur when this buffered solution reacts with: (a) added strong acid, H+, or (b) added strong base, OH-

Q1.

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

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