Calculate the pH of a 0.100 M CH₃NH₃Cl solution.K_b for methylamine,CH₃NH₂,is 3.7 × 10^-4. A)2.22 B)5.78 C)8.22 D)11.78

Question

Quizplus · Accepted Answer

CH3NH2 is a weak base, and the equation for its reaction with water is:

CH3NH2 + H2O ⇌ CH3NH3+ + OH-

The equilibrium constant expression for this reaction is:

Kb = [CH3NH3+][OH-] / [CH3NH2]

We are given the Kb value as 3.7 × 10-4. We can assume that the concentration of CH3NH3+ at equilibrium is very small compared to the initial concentration of CH3NH2, so we can simplify the expression as:

Kb = [OH-]2 / [CH3NH2]

Solving for [OH-]:

[OH-] = √(Kb × [CH3NH2]) = √(3.7 × 10-4 × 0.100) = 1.21 × 10-3 M

The pH is then calculated as:

pH = 14 - pOH = 14 - (-log[OH-]) = 5.78

Calculate the PH of a 0