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The third exam will be a week from today, April 16th,2008 in Marc s 131. It will cover chapters 2008 Marcus 131 ill co er 17-18. ... 1 Interesting Talk Today: ... 2 You want to buffer a solution at pH = 4.30. Which conjugate pair would you select? Ka A. HSO4- / SO421.2 x 10-2 B. CH3CO2H / CH3CO21.8 x 10-5 C. H2PO4-/HPO426.2 x 10-8 D. HCN / CN4.0 x 10-10
3 You Y want to buffer a solution at pH = 4.30. Wh t t t b ff l ti t H 4 30 What ratio of acid to conjugate acid would you select? A. 1 : 3.25 B. B 1 : 5.2 52 C. 1 : 1 D. 1.24:1 E. 2.78 : 1
4 ... 5 ... 6 Preparing a Buffer
A final point — Specific CONCENTRATIONS of the acid and conjugate base are not important. important. It is the _______________________of acid & _______________________of conjugate base. Result: diluting a buffer solution does not change its ________. g ________ To make a buffer you should select a conjugate pair where the ____ is in the same range as the desired _____.
7 An aqueous solution contains 0.320 M ammonia. Calculate the pH of the solution after the addition of 5.00x10-2 moles of hydrobromic acid to 225 mL of this solution. (Assume that the volume does not change upon adding HBr) acid). ... 8 ... 9 What was the compound that made the boiled cabbage water the purple at pH 6 but red at pH 2? t H b t d t H A.Anthocyanin B.A base C.A C A pH indicator D.A buffer E.An acid
10 Types of Acid/Base Reactions: Summary ... 11 Strong acid titrated with a strong base ... 12 ... 13 AcidAcid-Base Titrations Adding NaOH from the buret to acetic acid in the flask, a weak acid. In the beginning the pH increases very slowly. ... 14 AcidAcid-Base Titrations Additional NaOH is added. pH rises as equivalence point is approached. ... 15 AcidAcid-Base Titrations Additional NaOH is added. pH increases and then levels off as NaOH is added beyond the equivalence point. ... 16 halfhalf-way point equivalence point p pH of solution of benzoic acid, a weak acid
17 Benzoic acid + NaOH ... Acetic acid titrated with NaOH ... 18 Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH) ... 19 Weak base (NH3) titrated with a strong acid (HCl) ... 20 Titrations
pH Titrant volume, mL
21 This is the titration of a 1. Strong acid with strong base? 2. Weak acid with strong base? 3. Strong base with weak acid? g 4. Weak base with strong acid? 5. Weak base with weak acid 6. Weak acid with weak base? pH Volume of titrating reagent added --> -->
22 QUESTION: You titrate 100. mL of a 0.025 M solution of benzoic acid with 0.100 M NaOH to the equivalence point. pH at halfhalf-way point? pH at equivalence point? p pH of solution of benzoic acid, a weak acid
23 Benzoic acid + NaOH ... ...
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- Spring '08