Posted by Terence on .
Calculate how many milliliters of 0.100 M HCl must be added to 25.0 ml of a 0.200 M solution of NH3 to prepare a buffer that has a pH of 9.50? Kb = 1.76 x 10^5

Chemistry II 
DrBob222,
.............NH3 + HCl ==> NH4Cl
initial.....5 mmoles..0.....0
add..................x.........
change......x.......x.......+x
equil........5.x......0.......+x
Plug that into the HedersonHasselbalch equation.
pH = pKa + log (base/(acid)
Substitute into the HH equation and solve for x which will be mmols HCl.
Then M = mmoles/mL and solve for mL.
Post your work if you get stuck.