review3s08 - Dr McCord CH302 OVERVIEW for EXAM 3 Spring...

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Textbook Chapters for Exam 3 Chapters 8 (all of it) and Chapter 11 sections 1-3. You’re responsible for any material covered in class whether it was on the homework or not. This review sheet covers most everything we have done. Also remember that no equations are given on the exams. Values for equilibrium constants and any standard potentials are given where needed. Chapter 8 – Buffers, pH curves, Titra- tions, and Indicators • Know the basic premise for making a buffer solution . These are “type 2” problems according to Dr. McCord (see acid/base help sheets on our web site) • Know HOW a good buffer will neutralize both acid and/or base. Yes, this means know the actual reactions that do the neu- tralizing. • What is buffer capacity (section 8.4)? • Be able to use and identify the Henderson-Hasselbalch equations for both acids and bases. • Be able to calculate the pH of any buffer, acidic or basic. • What is the common ion effect ? Know the 2 ways to prepare buffers: 1. Mix the two conjugates with proper molar ratios: e.g. HA and NaA 2. Partial neutralization. : e.g. Neutralize a portion of HA with NaOH to MAKE the A - needed. You are essentially doing a titration but stopping somewhere in the middle. After all, that IS where you will have a nice mixture of BOTH acid and conjugate base. • Be able to calculate the new pH of a buffer AFTER the addi- tion of strong acid or strong base. Remember that you will al- ways be subtracting from one species and adding to the other in this calculation. For example, if my acid/conjugate base ratio is 50 mmol HA and 50 mmol A - and I add 15 mmol of OH - . After the addition the HA is now 50 - 15 = 35 mmol, and the A - is now 50 + 15 = 65 mmol. That 65/35 ratio is the new ratio that governs the buffer pH. • Know how to interpret a pH curve and get the stoichiometric point (aka: equivalence point) and the p K a (or p K b ) for a weak acid (or base). • In general, what's the pH at the stoichiometric point of a titra-
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review3s08 - Dr McCord CH302 OVERVIEW for EXAM 3 Spring...

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