Buffer CHemistry Handout

Buffer CHemistry Handout - pH: Buffers. A. Introduction. 1...

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pH: Buffers. A. Introduction. ................................................................................................... 1 B. Overview. ....................................................................................................... 1 C. Reversing reversible reactions . ...................................................................... 2 D. The acetic acid equilibrium: quantitative re-examination . ............................ 4 E. Generalizing The Henderson-Hasselbalch equation . ................................. 7 F. Choosing a buffer. .......................................................................................... 9 G. Some misconceptions . ................................................................................. 10 H. What does “buffer capacity” mean? . ........................................................... 11 I. Answers. ........................................................................................................ 11 J. Table of buffers. ............................................................................................ 13 A. Introduction This handout follows Weak Acids. It is the final topic handout. Frequent reference is made to the previous handouts of the pH series: Water (W), Strong Acids (SA) and Weak Acids (WA). As with WA, the emphasis here is on qualitative ideas. Quantitative material is presented to show you that our qualitative conclusions have a quantitative basis. Further, some of you may want to follow the quantitative issues more carefully. The equations are not particularly difficult, but they can get tedious. As a practical matter, most lab work involving buffers requires primarily a qualitative understanding. B. Overview A buffer is a solution that resists changes in pH . If you add some acid or base to a buffer, the pH changes less than “expected” . [More precisely, we might refer to such a solution as an acid-base buffer. We can have solutions that buffer other things. For example, we might use a calcium ion buffer, to control [Ca 2 + ]. But acid-base (or hydrogen ion) buffers are most common, and we often call them simply buffers, for convenience. If you do need to deal with buffers for other things, the logic is similar.] Buffers work because of the behavior of weak acids; you got some hints of the basis of buffer action in WA. You know that a given concentration of a weak acid gives off less H + than the same concentration of a strong acid -- because the weak acid is only partly ionized. And you saw that adding more of the acid causes a bigger change in a strong acid solution than in a you add some strong acid to a solution of a partially ionized weak acid; we will do that here.
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pH: Buffers. Page 2 We also briefly introduced the idea that acetate ion is itself a weak base, the conjugate base of acetic acid (end of Sect J-WA). C.
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This note was uploaded on 03/14/2011 for the course CHEM 237 taught by Professor Andersen during the Spring '08 term at University of Washington.

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Buffer CHemistry Handout - pH: Buffers. A. Introduction. 1...

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