Dimethylamine, (ch3) 2nh, has a kb value of 5.4 x 10â4. in a 1.2 m solution of dimethylamine at 25Ëc what is the concentration of h3o+?

Answer is:

concentration of H₃O⁺ is 4·10⁻¹³ mol/L.

Chemical reaction: (CH₃) ₂NH + H₂O → (CH₃) ₂NH₂⁺ + OH⁻. Kb ((CH₃) ₂NH) = 5,4·10⁻⁴. c ((CH₃) ₂NH) = 1,2 mol/L. Kb ((CH₃) ₂NH) = c (OH⁻) · c ((CH₃) ₂NH₂⁺) : c ((CH₃) ₂NH). c (OH⁻) = c ((CH₃) ₂NH₂⁺) = x. 5,4·10⁻⁴ = x² : 1,2-x.

Solve quadratic equation:

x = 0,025 mol/L. c (OH⁻) · c (H₃O⁺) = 10⁻¹⁴. c (H₃O⁺) = 10⁻¹⁴ : 0,025 = 4·10⁻¹³ mol/L.