Posted by kim on Friday, October 8, 2010 at 10:30pm.
.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
chemistry - kim, Friday, October 8, 2010 at 10:37pm
do i work this out the same way i do a pH problem with one volume?
chemistry - DrBob222, Friday, October 8, 2010 at 10:45pm
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.
chemistry - kim, Friday, October 8, 2010 at 10:47pm
I have tried using that equation but I keep getting 4.something. My answer should be around 9.
chemistry - DrBob222, Friday, October 8, 2010 at 10:51pm
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.
chemistry - kim, Friday, October 8, 2010 at 10:53pm
Thank you, I was using the wrong one.
chemistry - DrBob222, Friday, October 8, 2010 at 11:03pm
I'm glad things worked out for you. By the way, I meant, of course, PKa = 9.25 (not Ka) and pKb = 4.76
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