Class Notes Feb 01

Class Notes Feb 01 - 2/1/2010 Announcements: Monday,...

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2/1/2010 1 Announcements: Monday, February 1, 2010 Homework WebAssign #4- Due Wednesday, February 3 at 8:00 AM Recitation Week 4- “Acid/Base Properties” Lab 2- Buffers Complete prelab prior to recitation. Suggested Textbook Questions Continue Chapter 19 problems. What is the correct chemical reaction when LiOH is added to an HF/F - buffer? January 29, 2010 – CT#2 A. F - + LiOH LiF + OH - B. HF + H O F - + H O + D. F - + H 2 O HF + OH - E. F - + H 3 O + → HF + H 2 O C. HF + OH - → F - + H 2 O Strong base (OH - ) will react completely with HF until one is used up. If HF is the limiting reagent, then it isn’t a buffer anymore! Preparing a Buffer First, pick an acid with pK a desired pH. Next, use Henderson-Hasselbalch eqn to get the [base]/[acid] ratio or moles base/moles acid ratio. Ex. What is the base to acid ratio for a pH 4.25 HC 2 H 3 O 2 buffer? [A - ] [HA] pH = pK a + log 4.25 =4.74 + log [A - ] [HA] 10 -0.49 = 0.324 = [A - ] [HA] Now there are three ways to get this base/acid ratio. -0.49 = log [A - ] [HA] Preparing a Buffer There are three ways to get the correct base/acid ratio.
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Class Notes Feb 01 - 2/1/2010 Announcements: Monday,...

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