A question from my first analytical chemistry course, and I'm having a hard time fully comprehending the subject:
How many moles of Ammonium Sulfate should be added to a 320mL 0.105M solution of NH3 to get a solution with a pH of 9.35? Kb(NH3)=1.8e-5 M
Attempt:
I used the buffer equation:
POH=PKb+log([NH4+]/[NH3])
4.65=4.74+log([NH4+]/0.105]
[NH4+]=0.084M
the way I see it, this is the desired concentration of NH4+ in the solution.
The problem is I already have NH4+ forming in the solution even before adding the salt, because of the reaction NH3+H20 <-> NH4+ + OH-
so I just cant say "I have Y, I'll add X, and I'll have X+Y" because its an equilibrium.
Help would be appreciated