a) An acetic acid/sodium acetate buffer is made that is 0.42 M in HAc and 0.42 M

Question

a) An acetic acid/sodium acetate buffer is made that is 0.42 M in HAc and 0.42 M in NaAc. Calculate the pH after 0.024 mol of HCl is added to 1.0 L of the buffer. (Assume no volume change.)

b) Calculate the pH of a buffer solution which is 0.24 M in HNO2 and 0.43 M in NaNO2.
Ka of HNO2 = 4.6x10-4 at 25oC

d) Which of the following statements about buffers is/are true?

-A buffered solution containing 1.0 M HF and 1.0 M NaF has a smaller buffer capacity than one containing 0.10 M HF and 0.10 M NaF.

-In a buffer, when the [H+] = Ka, the acid concentration is greater than the conjugate base concentration.

-When a small amount of strong acid or base is added to a buffer, the pH changes only slightly.

Explanation / Answer

pH = pKa + log(A-/HA)

[A-] = 0.42 mol

[HA] = 0.42

when reaction takes place:

H+ = 0.024 mol / 1L

[HA] = 0.42+0.024 = 0.442

pKa = 4.75

pH = 4.75+ log(0.42-/0.442)= 4.727

b)

HNO3= 0.24

NaNO2 = 0.43

4.6x10-4

pH = pka + log(A-/HA)

pH = -log(4.6x10-4) + log(0.43/0.24) =3.59

pH = 3.59

d)

i) True (ratios A-/HA will differ)

ii) No, they are equal, ratio A- and HA is the same, therefore log(1) = pKa = pH

iii) True, pH wont be affected that much

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

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