Chemistry - Sri2734 yesterday at 8:11pm
1) Find the pH of 0.54 M C5H5N(aq) given that its Kb = 1.7×10^-9.
The answer I got is 2.75 but I got it wrong. The answer is supposed to be 9.48. Why?
2) Find the pH of a 0.864 M NH4Cl solution given that the Kb of NH3 = 1.8x10^-5 at 25 °C.
How would I start off this?
As Kw = KaKb (for conjugate acid/base pair)
Ka(C5H5NH+) = Kw/(1.7x10-9) = 5.9x10-6
For the dissociation of a weak acid:
Ka = [H+][A-]/[HA]
As [H+] = [A-] and [HA] ~ 0.54M
5.9x10-6 = [H+]² / 0.54
[H+] = √(0.54 x 5.9x10-6) = 0.00178493697
pH = -log[H+] = -log(0.001875) = 2.72