The weak base ethylamine (C2H5NH2 (aq)) has a Kb of 6.4 x10-4. Concentration of C2H5NH2 for pH? Equilibrium equation?

2020-07-15 2:43 pm

The weak base ethylamine (C2H5NH2 (aq)) has a Kb of 6.4 x10-4.
a) Write the equilibrium equation for the ionization of ethylamine. b) What concentration of C2H5NH2 (aq) is required to produce an ethylamine solution with a pH of 12.102?

回答 (1)

micatkie

2020-07-15 3:15 pm

✔ 最佳答案

_                 C₂H₅NH₂(aq) + H₂O(ℓ) ⇌ C₂H₅NH₃⁺(aq) + OH⁻(aq)   Kb = 6.4 × 10⁻⁴
_Initial:            x M              0 M       0 M
_Change:     -y M            +y M         +y M
_Equilibrium: (x - y)M           y M       y M

At equilibrium:
[OH⁻] = y M = 0.01265 M
y = 0.01265

Kb = [C₂H₅NH₃⁺] [OH⁻(aq)] / [C₂H₅NH₂]
6.4 × 10⁻⁴ = y² / (x - y)
6.4 × 10⁻⁴ = 0.01265² / (x - 0.01265)
x = 0.01265 + [0.01265² / (6.4 × 10⁻⁴)]
x = 0.263

Concentration of C₂H₅NH₂ = 0.263 M

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