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I am having some trouble figuring out how to approach the following problem: A 75.0-mL volume of 0.200 M NH3 (Kb=1.8×10−5) is titrated with 0.500 M HNO3. Calculate the pH after the addition of 17.0mL of HNO3.

Verified Answer :

johnkellock

We look at the end of the day:

n(HNO3) added = 0.50017.0/1000 = 0.00850 mol
n(NH3) = 0.20075.0/1000 - 0.00850 = 0.00650 mol
[NH3] left = 0.006501000/(17.0+75.0) = 0.070652
M [OH-] = Kb [NH3] = 0.0706521.810^(-5) = 1.27174 x 10^(-6)
pOH = -log[OH-] ≈ 5.8956 pH = 14 - pOH ≈ 8.10

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