A buffer solution contains 0.492 M ammonium chloride and 0.379 M ammonia. If 0.0
ID: 1031300 • Letter: A
Question
A buffer solution contains 0.492 M ammonium chloride and 0.379 M ammonia. If 0.0371 moles of potassium hydroxide are added to 225 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume change does not change upon adding potassium hydroxide) pH =
A buffer solution contains 0.222 M nitrous acid and 0.497 M potassium nitrite. If 0.0419 moles of hydroiodic acid are added to 225 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume change does not change upon adding hydroiodic acid) pH =
Explanation / Answer
1)
moles of NH4Cl = 0.492 x 0.225 = 0.1107
moles of NH3 = 0.379 x 0.225 = 0.0853
moles of KOH = 0.0371 mol
pOH = pKb + log [salt - C / base + C]
= 4.74 + log [0.1107 - 0.0371 / 0.0853 + 0.0371]
pOH = 4.52
pH = 9.48
2)
moles of HNO2 = 0.222 x 0.225 = 0.04995
moles of KNO2 = 0.497 x 0.225 = 0.1118
moles of HI = 0.0419 mol
pH = pKa + log [salt - C / acid + C]
= 3.25 + log [0.1118 - 0.0419 / 0.04995 + 0.0419]
pH = 3.13
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