Class Note for CHEM 122 at UMass(31)
Class Note for CHEM 122 at UMass(31)
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This 2 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 16 views.
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Date Created: 02/06/15
Chapter 11 Lecture Worksheet 1 Answers Which of the following aqueous solutions are good buffer systems 1 031 M acetic acid 026 M potassium acetate Weak acid Conjugate Base Yes 2 022 M potassium bromide 026 M hydrobromic acid Neutral salt Strong acid No 3 026 M ammonium bromide 034 M ammonia Conjugate acid Weak Base Yes 4 021 M hydrochloric acid 019 M hydrocyanic acid Strong acid Weak Acid No 5 016 M sodium hypochlorite 027 M barium hydroxide Conjugate weak Base Strong Base No Calculate the pH ofa solution containing 045 M hydro uoric acid Ka 72 X 10394 5 174 HF H20 lt gt H30aq Faq Initial 045 M 0 0 Change 1 E E Equilbl i m 045 X X X 7 2 2 Kawx L 72X104 HF 045 x 045 x z 1 045Ka 104572x104 00180 M H3O pH7log00180 174 If potassium uoride is added to the HF solution you would expect the reaction to shift 1 Right 2 Left to reestablish equilibrium If potassium uoride is added to the HF solution you would expect the pH to 1 Increase 2 Decrease 3 Remain the same at equilibrium Add conjugate base becomes more basic Calculate the pH of a solution containing 045 M hydro uoric acid and 045 M potassium uoride 8 314 HF H20 lt gt H30aq Faq Initial 045 M 0 045 Change 1 E E Equilbrium 045 X X 045 X H F 7 045 Ka w w x 72 x10394 M H301 HF 045 6 pH pKa 314 more basic For buffer solution in which weak acid conjugate base pH pKa If potassium hydroxide is added to the HFKF solution you would expect the pH to 1 Increase slightly if lt 045 M KOH added 4 Increase signi cantly if gt 045 M KOH added which exceeds the buffer capacity HF Use the Ka Table handed out previously to choose a buffer with a pH around 5 Look for KI around 10 5 so that pKa is approximately pH 5 Benzoic acid Benzoate anion Acetic acid Acetate anion Use the Ka Table handed out previously to choose a buffer with a pH around 10 Look for KI around 10 10 or K around 10quot so that pKa is approximately pH 10 Ammonia Ammonium cation Carbonate Hydrogen carbonate anions Lactic acid CZHSOCOOH is found in sour milk sauerkraut and in muscles a er activity K1 14 X 10394 Calculate the H of a solution containing 022 M sodium lactate NaC2H50COZ and 045 Mlactic acid PRS Answers 4 354 C2H50COOH H20 lt gt H30aq C2H50COO39aq Initial 045 M 0 022 Change 1 Equilbl i m 045 X X 022X H30C2H50C00 x022 x N 02216 CZHSOCOOH 045 x 045 Kg 14x10 4 x 04502214 x 10394 29 x 10394 M H301 pH flog X 354 Calculate the pH of the lactic acid buffer solution above AFTER the addition of 0050 M HCl assume no volume change PRS Answers 3 339 Add HCl strong acid Conjugate base consumed Weak acid produced Buffer replaces the added strong acid with the weak acid by consuming the conjugate base C2H50COOH H20 lt gt H30aq C2H50COO39aq Befnre 045 M 022 HCl 0050 M 0050 M Initial 050 M 0 017 M Change 1 E E Equilbrium 050 X X 017X Kg H30C2H50C00 x0 17 x z 017x CZHSOCOOH 050 x 050 14x10 4 x 05001714 x 10394 42 x 10394 M H301 pH flog X 339 Sightly more acidic How many grams of solid ammonium chloride should be added to 100 L of a 0221 M ammonia solution to prepare a buffer with a pH of 10160 pH 10160 NH4C1 1401 4101 3545 5350 gmol pOH 14000 10160 23840 OH 10 3 840 1445X104 M Look for NH40 and then calculate mass needed to get this concentration NH3aq H20 lt gt NH4aq OHaq Initial 0221 M NH40 0 Change 1 E E Equilbrium 0221 x Nmlo X X 2 0221 M z NHno 1445x10 1 M Wmsz NHS 0221 18x10395 b NH40 18X10 502211445X104 002752 M 002752mol NH4C15350g NHACZ g NH4C1 100L mol 147 g 15 g NH4C1
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