Question

Use the References to access Important values if needed for this question. In the laboratory, a general chemistry student mea
In the laboratory, a general chemistry student measured the pH of a 0.319 M aqueous solution of diethylamine, (CH2)2NH to be
In the laboratory, a general chemistry student measured the pH of a 0.443 M aqueous solution of methylamine, CH NH, to be 12.
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Answer #1

1)

use:

pH = -log [H+]

9.262 = -log [H+]

[H+] = 5.47*10^-10 M

use:

[OH-] = Kw/[H+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

[OH-] = (1.0*10^-14)/[H+]

[OH-] = (1.0*10^-14)/(5.47*10^-10)

[OH-] = 1.828*10^-5 M

B dissociates as:

B +H2O -----> BH+ + OH-

0.575 0 0

0.575-x x x

Kb = [BH+][OH-]/[B]

Kb = x*x/(c-x)

Kb = 1.828*10^-5*1.828*10^-5/(0.575-1.828*10^-5)

Kb = 5.812*10^-10

Answer: 5.812*10^-10

2)

use:

pH = -log [H+]

12.19 = -log [H+]

[H+] = 6.486*10^-13 M

use:

[OH-] = Kw/[H+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

[OH-] = (1.0*10^-14)/[H+]

[OH-] = (1.0*10^-14)/(6.486*10^-13)

[OH-] = 1.542*10^-2 M

B dissociates as:

B +H2O -----> BH+ + OH-

0.319 0 0

0.319-x x x

Kb = [BH+][OH-]/[B]

Kb = x*x/(c-x)

Kb = 1.542*10^-2*1.542*10^-2/(0.319-1.542*10^-2)

Kb = 7.829*10^-4

Answer: 7.829*10^-4

3)

use:

pH = -log [H+]

12.12 = -log [H+]

[H+] = 7.603*10^-13 M

use:

[OH-] = Kw/[H+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

[OH-] = (1.0*10^-14)/[H+]

[OH-] = (1.0*10^-14)/(7.603*10^-13)

[OH-] = 1.315*10^-2 M

B dissociates as:

B +H2O -----> BH+ + OH-

0.443 0 0

0.443-x x x

Kb = [BH+][OH-]/[B]

Kb = x*x/(c-x)

Kb = 1.315*10^-2*1.315*10^-2/(0.443-1.315*10^-2)

Kb = 4.024*10^-4

Answer: 4.024*10^-4

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