e. 4.7x 10 16. A buffer is composed of 0.400 mol H:POs and 0.400 mol HPO diluted

Question

e. 4.7x 10 16. A buffer is composed of 0.400 mol H:POs and 0.400 mol HPO diluted with water to a volume of 1.00 L. The pH of the buffer is 7.210. How many moles of HCl must be added to decrease the pH to 6.210? a. 0.200 mol b. 0.327 mol c. 0.360 mol d. 0.400 mol e. 3.60 mol 17. A buffer contains 0.50 mol NH and 0.50 mol NH diluted with water to 1.0 L. How many moles of NaOH are required to increase the pH of the buffer to 10.00? (pK, of NHa-9.25) a. 0.035 mol b. 0.15 mol c. 0.35 mol d. 0.41 mol e. 2.8 mol

Explanation / Answer

Q16

if we need

pH = 6.21

then

apply buffer equation

pH = pKa + log(HPO4-2 / H2PO4-)

pKa = 7.21 for 2nd ionizaiton

so

6.21 = 7.21 + log(HPO4-2 / H2PO4-)

(HPO4-2 / H2PO4-) = 10^(6.21-7.210) = 0.1

(HPO4-2 / H2PO4-) = 0.1

HPO4-2 = 0.1* H2PO4-

then

initially

H2PO4- = 0.4

HPO4-2 = 0.4

after adding x mol of HCl

H2PO4- = 0.4 + x

HPO4-2 = 0.4 - x

and we know

HPO4-2 = 0.1* H2PO4-

0.4 - x = 0.1* (0.4 + x)

0.4-x = 0.04 + 0.1x

1.1x = 0.4-0.04

x =  (0.4-0.04)/(1.1) = 0.3272

crom the list

choose B, 0.327

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

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