72-Buffer-Prob-Ans

72-Buffer-Prob-Ans - BUFFER ANALYSIS FOR GCHEM II CONCEPT...

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BUFFER ANALYSIS FOR GCHEM II CONCEPT PROBLEMS 1a. Calculate the pH of a buffer solution made from 0.380 M acetic acid (HC 2 H 3 O 2 ) and 0.150 M sodium acetate (NaC 2 H 3 O 2 ). The Ka acetic acid is 1.8 x 10 –5 . R eaction HC 2 H 3 O 2(a) + H 2 O (l) H 3 O +1 + C 2 H 3 O 2 -1 (a) + C 2 H 3 O 2 -1 (a) I nitial (M) .380 0 0 .150 C hange (+/–) – x + x + x E quilibrium (.380 – x) x (x + .150) Ka = [H 3 O +1 ] [C 2 H 3 O 2 -1 ] 1.8 x 10 -5 = (x)( x +.150) = (x) (.150 ) x = 4.56 x 10 -5 = [H 3 O +1 ] [HC 2 H 3 O 2 ] (.380 – x ) .380 pH = – log[H 3 O +1 ] = – log[4.56 x 10 -5 ] = 4.341 pH = 4.34 1b. Calculate the pH using Henderson Hasselbalch equation. pKa = –log[Ka] = – log[1.8 x 10 -5 ] = 4.741 pH = pKa + log [Conjuntive Base/Acid] = 4.471 + log ( x + .150)/(.380 – x ) pH = 4.741 + log [.3947] = 4.741 + .4037 = 4.337 pH = 4.34 2a. Calculate the pH of a buffer solution made from 200.0 mls of 0.150 M benzoic acid (HC 7 H 5 O 2 ) and 100.0 mls of 0.0150 M potassium benzoate (KC 7 H5O 2 ). The Ka benzoic acid is 6.30 x 10 –6 . R eaction
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This note was uploaded on 07/28/2011 for the course CHM 2046c taught by Professor Staff during the Summer '08 term at UNF.

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72-Buffer-Prob-Ans - BUFFER ANALYSIS FOR GCHEM II CONCEPT...

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