# Chemistry II

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

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1. .............NH3 + HCl ==> NH4Cl
initial.....5 mmoles..0.....0
change......-x.......x.......+x
equil........5.x......0.......+x

Plug that into the Hederson-Hasselbalch 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.

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