16.a.)A buffer solution contains 0.339 M ammonium bromide and 0.316 M ammonia. I
ID: 499876 • Letter: 1
Question
16.a.)A buffer solution contains 0.339 M ammonium bromide and 0.316 M ammonia. If 0.0573 moles of potassium hydroxide are added to 250 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume does not change upon adding potassium hydroxide) pH =
b.) A buffer solution contains 0.366 M NaH2PO4 and 0.344 M Na2HPO4. If 0.0305 moles of hydrobromic acid are added to 250. mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume does not change upon adding hydrobromic acid) pH =
c.) A buffer solution contains 0.273 M ammonium bromide and 0.348 M ammonia. If 0.0176 moles of nitric acid are added to 125 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume does not change upon adding nitric acid) pH =
Explanation / Answer
16.
a.)
millimoles of NH3 = 0.316 x 250 = 79
millimoles of NH4Br = 0.339 x 250 = 84.75
millimoles of KOH = 57.3
pOH = pKb + log [salt - C / base + C]
= 4.74 + log [84.75 - 57.3 / 79 + 57.3]
= 4.04
pH = 9.96
b.)
millimoles of NaH2PO4 = 0.366 x 250 = 91.5
millimoles of Na2HPO4 = 0.344 x 250 = 86
millimoles of HBr = 30.5
pH = pKa + log [salt - C / acid + C]
= 7.21 + log [86 - 30.5 / 91.5 + 30.5]
= 6.87
pH = 6.87
c.)
millimoles of NH3 = 0.348 x 125 = 43.5
millimoles of NH4Br = 0.273 x 125 = 34.125
millimoles of HNO3 = 17.6
pOH = pKb + log [salt + C / base - C]
= 4.74 + log [34.125 + 17.6 / 43.5 - 17.6]
= 5.04
pH = 8.96
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