Question

PART A

A buffer solution contains 0.358 M ammonium chloride and 0.499 M ammonia.

If 0.0274 moles of perchloric acid are added to 125 mL of this buffer, what is the pH of the resulting solution ?
(Assume that the volume change does not change upon adding perchloric acid)

pH = _______

PART B

A buffer solution contains 0.328 M nitrous acid and 0.481 M sodium nitrite.

If 0.0248 moles of hydrochloric acid are added to 125 mL of this buffer, what is the pH of the resulting solution ?
(Assume that the volume change does not change upon adding hydrochloric acid)

pH = _______

PART C

A buffer solution contains 0.342 M ammonium chloride and 0.337 M ammonia.

If 0.0625 moles of potassium hydroxide are added to 250 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 = _________

Answer 1

PART A

A buffer solution contains 0.358 M ammonium chloride and 0.499 M ammonia.

moles of NH4Cl = 0.358 x 0.125 = 0.04475

moles of NH3 = 0.499 x 0.125 = 0.0624

moles of HClO4 = 0.0274

pOH = pKb + log [salt + C / base - C]

        = 4.74 + log [0.04475 + 0.0274 / 0.06237 - 0.0274]

pOH = 5.05

pH = 8.94

b)

pKa = 3.25

moles of HNO2 = 0.328 x 0.125 = 0.041

moles of NaNO2 = 0.481 x 0.125 = 0.0601

moles of HCl = 0.0248 mol

pH = pKa + log [salt - C / acid + C]

     = 3.25 + log [0.0601 - 0.0248 / 0.041 + 0.0248]

pH = 2.98