What is the pH of 0.51 M diethylammonium bromide, (C2H5)2NH2Br. The Kb of diethylamine, (C2H5)2NH, is 6.9 x 10-4.

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What is the pH of 0.51 M diethylammonium bromide,(C₂H₅)₂NH₂Br.
The K_b of diethylamine,(C₂H₅)₂NH, is 6.9 x10^-4.

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(C₂H₅)₂NH₂Br it is a salt of strong acid and weak base. so cation participate in the reaction

(C₂H₅)₂NH₂⁺ + H2OÂ Â Â ---------------------> (C₂H₅)₂NH₂ + H3O+

Â Â Â 0.51Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 0Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 0

0.51 - xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â x

Ka = Kw / Kb = 1.0 x 10^-14 / 6.9 x 10^-4. = 1.45 x 10^-11

Ka = [ (C₂H₅)₂NH₂ ][H3O+] / [(C₂H₅)₂NH₂⁺ ]

1.45 x 10^-11 = x^2 / 0.51 - x

x = 2.71 x 10^-6

[H3O+] = x = 2.71 x 10^-6 M

pH = -log[H3O+]

Â Â Â Â Â = -log (2.71 x 10^-6)

Â Â Â Â Â = 5.57

pH = 5.57

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