1) A buffer solution contains 0.356 M ammonium chloride and 0.396 M ammonia . If
ID: 811760 • Letter: 1
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 = ____
Explanation / Answer
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
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