Triethylamine, N(C2H5)3, has a solubility of 68.6gL, a molar mass of 101.19gmol, and a base-ionization constant Kb=6.0×10−4. What is the pH of a saturated solution of triethylamine in water

Question

Triethylamine, N(C2H5)3, has a solubility of 68.6gL, a molar mass of 101.19gmol, and a base-ionization constant Kb=6.0×10−4. What is the pH of a saturated solution of triethylamine in water

Answer 1

The reaction of triethylamine in water is: N(C2H5)3 + H2O ==> HN(C2H5)3^+ + OH^-

Kb = 6.0x10^-4 = [HN(C2H5)3^+][OH^-]/[N(C2H5)3]

A saturated solution will be 68.6 g/L. Converting this to moles/L we have ...

68.6 g/L x 1 mole/101.19g = 0.6779 M

6.0x10^-4 = (x)(x)/0.6779

x^2 = 4.068x10^-4

x = 2.02x10^-2 = [OH-]

pOH = -log 2.02x10^-2 = 1.70

pH = 14 - pOH = 12.3