
Chemistry
10th Edition
ISBN: 9781305957404
Author: Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher: Cengage Learning
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Transcribed Image Text:Learning Goal:
To understand how buffers use reserves of
conjugate acid and conjugate base to counteract
the effects of acid or base addition on pH.
A buffer is a mixture of a conjugate acid-base pair
In other words, it is a solution that contains a weak
acid and its conjugate base, or a weak base and its
conjugate acid. For example, an acetic acid buffer
consists of acetic acid, CH₂COOH, and its
conjugate base, the acetate ion CH,COO
Because ions cannot simply be added to a solution,
the conjugate base is added in a salt form (e.g.
sodium acetate NaCH₂COO)
Buffers work because the conjugate acid-base pair
work together to neutralize the addition of Hor
OH ions. Thus, for example, it Hions are
added to the acetate buffer described above, they
will be largely removed from solution by the
reaction of H with the conjugate base:
H+CH₂COO-CH₂COOH
Similarly, any added OH ions will be neutralized
by a reaction with the conjugate acid
OH +CH₂COOH-CH₂COO+H₂O
This butter system is described by the Henderson-
Hasselbalch equation
pH=pK, +loggate ad
conjugate base
Part A
A beaker with 1.30x10 mL of an acetic acid butter with a pH of 5.000 is sitting on a benchtop. The total molarity of acid
and conjugate base in this buffer is 0.100 M. A student adds 8.10 mL of a 0.460 M HCl solution to the beaker How
much will the pH change? The pK, of acetic acid is 4.740
Express your answer numerically to two decimal places. Use a minus (-) sign if the pH has decreased.
View Available Hint(s)
ApH-
VAL
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