Calculate the pH and concentrations of CH 3 NH 2 and CH 3 NH + 3 in a 0.0317 M methylamine ( CH 3 NH 2 ) solution. The K b of CH 3 NH 2 is 4.47 × 10 − 4 .

[CH₃NH₃⁺] = 0.00355 M

[CH₃NH₂] = 0.028 M

pH = 11.55

Explanation:

The reaction is the following:

CH₃NH₂  +  H₂O  ⇄  CH₃NH₃⁺ + OH⁻       (1)

0.0317 - x                      x               x

The equilibrium constant of the reaction (1) is:

    (2)

By solving equation (2) for x, we have:

x₁ = -0.00399

x₂ = 0.00355

Taking the positive value, we have that:

x = [CH₃NH₃⁺] = [OH⁻] = 0.00355 M

[CH₃NH₂] = 0.0317 - x = (0.0317 - 0.00355)M = 0.028 M

Therefore, the concentrations of CH₃NH₂ and CH₃NH₃⁺ are 0.028 M and 0.00355 M, respectively.

The pH of the solution is:

Hence, the pH of the solution is 11.55.  

I hope it helps you!  

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).