For the titration of 20 0 mL of 0 125 M nitrous acid HNO_2 with 0 100 M sodium h

Question

For the titration of 20 0 mL of 0 125 M nitrous acid HNO_2 with 0 100 M sodium hydroxide, NaOH, answer the following questions and construct a titration curve (Please use pK_a = 3.34 for nitrous acid). What volume (in mL) of 0.100M sodium hydroxide is required to "neutralize" 20.0mL of 0.125M nitrous acid? What is the pH of the solution before any sodium hydroxide is added? What is the pH at the half-stoichiometric or half-equivalence point (that is what is the pH when you have added 1/2 of the total volume of base that would be required to react with all of the acid originally present)? What is the pH when 95% of the sodium hydroxide required to reach the stoichiometric point has been added? What is the pH at the stoichiometric point? What is the pH when a 5% excess of the sodium hydroxide required to reach the stoichiometric point has been added? Attach your graph to this test. DONT FORGET TO TITLE AND LABEL YOUR GRAPH! Although not specified in parts a-f, you should have data points up to twice the volume required to reach the equivalence point to create a proper graph.

Explanation / Answer

a)

millimoles of acid = millimoles of base

20 x 0.125 = V x 0.100

V = 25 mL

volume of NaOH = 25 mL

b)

pH = 1/2 [pKa - logC]

pH = 1/2 [3.34 -log 0.125]

pH = 2.12

c)

at half equivalence point : pH = pKa

pH = 3.34

e) at this point only salt remains

salt concentration = 20 x 0.125 / (20 +25) = 0.056 M

pH > 7

pH = 7 + 1/2 [pKa + logC]

pH = 7 + 1/2 [3.34 + log 0.056]

pH = 8.04

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.