Methylamine is an amine which is an organic weak base. Its chemical formula is CH₃NH₂. When it undergoes hydrolysis wherein water is acting as an acid, the reaction would be
CH₃NH₂ + H₂O ⇆ CH₃NH₃ + OH⁻
Then, we use the ICE analysis which stands for Initial-Change-Equilibrium.
CH₃NH₂ + H₂O ⇆ CH₃NH₃ + OH⁻
Initial 0.05 - 0 0
Change -x +x +x
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Equilibrium 0.05-x x x
Then, we use the equation for the equilibrium constant of basicity.
Kb = [CH₃NH₃][OH⁻]/[CH₃NH₂] = 4.4×10⁻⁴
4.4×10⁻⁴ = [x][x]/[0.05-x]
[x] = 4.4756×10⁻³
The variable x here denotes the number of moles of the substance that is involved in the reaction. Since the equilibrium amount of OH⁻ is equal to x, then the concentration of OH⁻ is also 4.4756×10⁻³. Thus,
pOH = -log[OH⁻]
pOH = -log[4.4756×10⁻³] = 2.35
The relationship between pOH and pH is that pH + pOH = 14. Thus,
pH = 14 - 2.35 = 11.65
pH = -log[H⁺]
11.65 = -log[H⁺]
[H⁺] = 2.234 × 10⁻¹² M
