Question

1) A buffer solution contains 0.356 M ammonium chloride and 0.396 M ammonia.
If 0.0550 moles of hydroiodic 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 hydroiodic acid)

pH=____

2) A buffer solution contains 0.354 M NaH₂PO₄ and 0.393 M K₂HPO₄.
If 0.0412 moles of sodium hydroxide are added to 225 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume does not change upon adding sodium hydroxide)

pH = ___

3) A buffer solution contains 0.341 M nitrous acid and 0.235 M sodium nitrite.
If 0.0278 moles of sodium 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 sodium hydroxide)

pH = ____

Answer 1

1) pH = 14- {pKb + log[salt/base]}

after addition of acid to basic buffer salt concentrion increase and base conc decreces

   pH = 14- {pKb + log[salt +C/base-C]}

HI moarity = 0.055x1000/250=0.22M

          pH = 14- {pKb + log[salt +C/base-C]}

pH = 14- {4.74+ log[0.356 +0.22/0.396-0.22]}

     = 8.74

2) on addition of base to basic buffer salt conc decrese and base conc increse

      NaOH conc =0.183M

pH = 14- {pKb + log[salt -C/base+C]}

          = 14- {6.79 + log[0.393 -0.183/0.0412+0.183]}

         = 7.23

3) on addition of base to acidic buffer salt conc increase and acid con decrese

NaOH conc=0.11M

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

pH = 3.39 + log[0.235 +0.11/0.341-0.11]

     = 3.56