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General Chemistry Principles, Patterns, and Applications, 2011

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. Sodium pentanoate is added to make a buffered solution. What is the pH of the solution if<br />

it is 0.210 M in sodium pentanoate?<br />

c. What is the final pH if 8.00 mL of 0.100 M HCl are added to 75.0 mL of the buffered<br />

solution?<br />

d. What is the final pH if 8.00 mL of 0.100 M NaOH are added to 75.0 mL of the buffered<br />

solution?<br />

A N S W E R<br />

1.<br />

2.<br />

3.<br />

a. 1.35 × 10 −3<br />

b. 4.03<br />

c. 3.88<br />

d. 4.30<br />

16.6 Buffers<br />

L E A R N I N G O B JE C T I V E S<br />

1. To underst<strong>and</strong> how adding a common ion affects the position of an acid–base<br />

equilibrium.<br />

2. To know how to use the Henderson-Hasselbalch equation to calculate the pH of a buffer.<br />

Buffers are solutions that maintain a relatively constant pH when an acid or a base is added. They therefore protect,<br />

or “buffer,” other molecules in solution from the effects of the added acid or base. Buffers contain either a weak acid<br />

(HA) <strong>and</strong> its conjugate base (A − ) or a weak base (B) <strong>and</strong> its conjugate acid (BH + ), <strong>and</strong> they are critically important for<br />

the proper functioning of biological systems. In fact, every biological fluid is buffered to maintain its physiological pH.<br />

The Common Ion Effect<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1541

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