12/8/2014 11:00 PM A 6/20 12/5/2014 10:23 PM PrintCalculatorPeriodic Table Grade

Question

12/8/2014 11:00 PM A 6/20 12/5/2014 10:23 PM PrintCalculatorPeriodic Table Gradebook Question 5 of 10 University Science Books presented by Sapling Learning Donald McQuarrie. Peter A. Rock Ethan Gallogly You need to prepare 100.0 mL of a pH-4.00 buffer solution using 0.100 M benzoic acid (pKa 4.20) and 0.180 M sodium benzoate. How much of each solution should be mixed to prepare this buffer? Number mL benzoic acid Number mL sodium benzoate L. sodium benzoate Hint 0 Previous Give Up & View Solution Check Answer 0 NextExit -

Explanation / Answer

pH=pKa + log [sodium benzoate]/[benzoic acid] [Hendersen's equation]

4 = 4.20 + log (0.18Vb / 0.1Va)
Vb/Va = 0.39
Vb= 0.39 Va (1)
Vb + Va = 100 (2)

equating the two equations

0.39 Va + Va = 100
Va= 71.94 ml

so
Vb= 28.06 ml

Thus , 71.94 ml of acid and 28.06 ml of salt of acid should be used to create a buffer with pH=4.

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