Please help!! 2/28/2016 12:05 AM 2/28/2016 12:05 AM O 472/1002/27/2016 09:16 AM

Question

Please help!!

2/28/2016 12:05 AM 2/28/2016 12:05 AM O 472/1002/27/2016 09:16 AM Gradebook Print Calculator Periodic Table Question 2 of 12 Map a sapling learning A buffered solution containing dissolved aniline, CsH5NH2, and aniline hydrochloride, CsH5NH3Cl, has a pH of 5.32 a) Determine the concentration of CsHsNH3* in the solution if the concentration of CeHsNH2 is 0.335 M. The pKb of aniline is 9.13 Number b) Calculate the change in pH of the solution, if 0.367 g NaOH is added to the buffer for a final volume of 1.50 L. Assume that any contribution of NaOH to the volume is negligible. Number O Previous ) Check AnswerNext Exit Hint

Explanation / Answer

a) Using Hendersen-Hasselbalck equation,

pH = pKa + log([C6H5NH2]/[C6H5NH3+])

when,

[C6H5NH2] = 0.335 M

pKa = 14 - pKb = 14 - 9.13 = 4.87

we get,

5.32 = 4.87 + log(0.335/[C6H5NH3+])

Thus, [C6H5NH3+] = 0.12 M

b) When 0.367 g NaOH = 0.367 g/40 g/mol = 0.0092 mols added

Final molar concentration of,

[C6H5NH2] = (0.335 x 1.5 + 0.0092)/1.5 = 0.341 M

[C6H5NH3+] = (0.12 x 1.5 - 0.0092)/1.5 = 0.114 M

pH = 4.87 + log(0.341/0.114)

     = 5.34

change in pH = 5.32 - 5.34 = 0.02

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