You have 20.00 mL of a 0.1M aqueous solution of the weak base (CH3)3N (Kb = 7.4x10^-5). This solution will be titrated with 0.100 M HCl.

Question

You have 20.00 mL of a 0.1M aqueous solution of the weak base (CH3)3N (Kb = 7.4x10^-5).  This solution will be titrated with 0.100 M HCl.

How do you find the pH of this solution before any acid has been added.

DrBob222 · Answer

To save typing I will call (CH3)3N--triethyl amine--RN
...........RN + HOH ==> RNH^+ +OH^-
initial....0.1............0....0
change.....-x............x......x
equil......0.1-x.........x......x

Kb = (RNH^+)(OH^-)/(RN)
Substitute from the ICE chart above into Ka expression and solve for x = (OH^-) and convert to pH.