Consider how best to prepare one liter of a buffer solution with pH = 7.91 using

Question

Consider how best to prepare one liter of a buffer solution with pH = 7.91 using one of the weak acid/conjugate base systems shown here.

HC2O4-

C2O42-

6.4 x 10-5

4.19

H2PO4-

HPO42-

6.2 x 10-8

7.21

HCO3-

CO32-

4.8 x 10-11

10.32

How many grams of the sodium salt of the weak acid must be combined with how many grams of the sodium salt of its conjugate base, to produce 1.00 L of a buffer that is 1.00 M in the weak base?

grams sodium salt of weak acid =

grams sodium salt of conjugate base =

Weak Acid Conjugate Base Ka pKa

HC2O4-

C2O42-

6.4 x 10-5

4.19

H2PO4-

HPO42-

6.2 x 10-8

7.21

HCO3-

CO32-

4.8 x 10-11

10.32

Explanation / Answer

pH = 7.91

pKa = 7.21

pH = pKa + log [Na2HPO4 / NaH2PO4]

7.91 = 7.21 + log [Na2HPO4 / NaH2PO4]

[Na2HPO4 / NaH2PO4] = 5.012

1 / NaH2PO4 = 5.012

NaH2PO4 = 0.120 moles

NaH2PO4 = 0.120 x 120 = 23.94 g

grams sodium salt of weak acid = 23.94 g

grams sodium salt of conjugate base = 142 g

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

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