What is the pH of a 0.050M triethylamine, (C2H5)3N, solution? Kb for triethylamine is 5.3 x 10^-4
I have no idea how to start this, thanks.
To determine the pH of a solution of triethylamine, (C2H5)3N, you need to consider the basicity of the compound and the value of its base dissociation constant (Kb).
Triethylamine, (C2H5)3N, is a weak base that dissociates in water to produce hydroxide ions (OH-) and its conjugate acid, triethylammonium (C2H5)3NH+.
The dissociation reaction is represented as follows:
(C2H5)3N + H2O ⇌ (C2H5)3NH+ + OH-
The base dissociation constant, Kb, is the equilibrium constant for this reaction and is given as 5.3 x 10^-4. It can be used to calculate the concentration of OH- ions, which then helps in determining the pH of the solution.
To find the concentration of OH- ions, you can set up an ICE (Initial, Change, Equilibrium) table:
(C2H5)3N + H2O ⇌ (C2H5)3NH+ + OH-
Initial: 0.050 M 0 M 0 M
Change: -x +x +x
Equilibrium: 0.050 - x x x
Since triethylamine is a weak base, it does not dissociate completely. Thus, we can approximate the value of x as negligible.
Therefore, the concentration of [OH-] = x = 0 M.
To find the pOH, which is the negative logarithm of the OH- concentration, we can substitute the value of [OH-] into the equation:
pOH = -log10[OH-]
pOH = -log10(0)
Since taking the logarithm of zero is undefined, we can conclude that the concentration of hydroxide ions ([OH-]) is negligible in the solution.
Now, to find the pH, which is the negative logarithm of the hydrogen ion concentration ([H+]), we can use the equation:
pH + pOH = 14 (at 25°C)
Therefore, as the pOH is undefined, the pH is also undefined for this solution.
In summary, the pH of the 0.050 M triethylamine solution is undefined due to the negligible concentration of hydroxide ions formed from the dissociation of triethylamine.