Calculate the change in pH when 0.28 mol H^+ is added to 1.00 L of each of the f
ID: 495995 • Letter: C
Question
Calculate the change in pH when 0.28 mol H^+ is added to 1.00 L of each of the following buffers: (a) a 0.58 M solution of pyridine (py) containing 0.52 M pyH^+, (b) a 0.60 M solution of aniline (an) containing 0.92 M anH^+. Did you use the Henderson-Hasselbalch equation to find initial pH values? Remember, the Henderon-Hasselbalch equation is written in terms of pH and pKa. What is the effect of adding a strong acid (H^+) to a buffer? Did you calculate the concentrations of base and conjugate acid after the addition of H^+? Did you find the new pH of each buffer? Did you calculate the change in pH for both solutions?Explanation / Answer
a)
pyridine = 0.58
pyH+ = 0.52
pKb of pyridine = 8.77
pOH = pKb + log [salt / base]
= 8.77 + log [0.52 /0.58]
= 8.72
pHinitial = 5.28
C= moles of H+ = 0.28 M
pOH = pKb + log [salt + C / base - C]
= 8.77 + log [0.52 + 0.28 / 0.58 - 0.28]
= 9.20
pH fianl = 4.80
pH change = 4.80 - 5.28 = - 0.48
pH change = - 0.48
b)
anilinie pKb = 9.13
pOH = pKb + log [salt / base]
= 9.13 + log [0.92 /0.60]
= 9.32
pH = 4.68
pOH = pKb + log [0.92 + 0.28 / 0.60 - 0.28]
= 9.13 + log [0.92 + 0.28 / 0.60 - 0.28]
= 9.70
pH = 4.30
pH change = 4.30 - 4.68 = - 0.38
pH change = - 0.38
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