Question

In: Chemistry

A. In the laboratory, a general chemistry student measured the pH of a 0.538 M aqueous...

A. In the laboratory, a general chemistry student measured the pH of a 0.538 M aqueous solution of ethylamine, C₂H₅NH₂ to be 12.198.
Use the information she obtained to determine the K_b for this base

B. She then measured the pH of a 0.538 M aqueous solution of methylamine, CH₃NH₂ to be 12.161.
Use the information she obtained to determine the K_b for this base

(these are 2 parts of the same question, please answer both!! :-) thank you! )

Expert Solution

A)

C2H5NH2 + H2O ------------> C2H5NH3+ + OH-

0.538 0 0

0.538 - x x x

pH = 12.198

pOH = 1.802

[OH-] = 0.01578 M

Kb = x^2 / 0.538 - x

= (0.01578)^2 / 0.538 - 0.01578

Kb = 4.77 x 10^-4

B)

CH3NH2 + H2O ------------> CH3NH3+ + OH-

0.538 0 0

0.538 - x x x

pH = 12.161

pOH = 1.839

[OH-] = 0.01449 M

Kb = x^2 / 0.538 - x

= (0.01449 )^2 / 0.538 - 0.01449

Kb = 4.01 x 10^-4

queen_honey_blossom answered 2 years ago

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