Methylamine (ch3nh2) is a weakly basic compound. calculate the kb for methylamine if a 0.253 m solution is 4.07% ionized.

Question

Valentin Foster

Chemistry

19 August, 17:57

Methylamine (ch3nh2) is a weakly basic compound. calculate the kb for methylamine if a 0.253 m solution is 4.07% ionized.

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Everett Stephens · Answer 1

Answer is: Kb for methylamine is 4.37·10⁻⁴.

Chemical reaction: CH ₃NH₂ + H₂O → CH₃NH₃⁺ + OH⁻.

c (CH₃NH₂) = 0.253 M.

α = 4.07% : 100% = 0.0407.

[CH₃NH₃⁺] = [OH⁻] = c (CH₃NH₂) · α.

[CH₃NH₃⁺] = [OH⁻] = 0.253 M · 0.0407.

[CH₃NH₃⁺] = [OH⁻] = 0.0103 M.

[CH₃NH₂] = 0.253 M - 0.0103 M.

[CH₃NH₂] = 0.2427 M.

Kb = [CH₃NH₃⁺] · [OH⁻] / [CH₃NH₂].

Kb = (0.0103 M) ² / 0.2427 M.

Kb = 4.37·10⁻⁴.