Question

.70 L of a buffer solution that is 0.120 M in NH3 and 0.450 M in NH4Cl are diluted to 5.80 L with distilled water. What is the pH of the buffer? Kb of NH3 = 1.8 x 10^-5

Answer 1

do i work this out the same way i do a pH problem with one volume?

Answer 2

I don't know how YOU work it out. That may work depending upon how you do it.
I would use the Henderson-Hasselbalch equation.

Answer 3

I have tried using that equation but I keep getting 4.something. My answer should be around 9.

Answer 4

I expect you are using the wrong Ka.
Ka for NH3 is NOT 4.76. It is 9.25.
Using the HH equation, I obtained 8.68 with a quickie calculation but check me out on that.

Answer 5

Thank you, I was using the wrong one.

Answer 6

I'm glad things worked out for you. By the way, I meant, of course, PKa = 9.25 (not Ka) and pKb = 4.76