please show all steps For each of these desired pH values, choose a weak acid-co

Question

please show all steps

For each of these desired pH values, choose a weak acid-conjugate base pair from your textbook that could be used to prepare a buffer solution with that pH Calculate the desired [A VIHA] ratio in each case. (a) pH = 6.00 1. (b) pH = 8.00 (c) pH = 11.00 2. 500 mL of a buffer solution contains 0.050 mol NaHSO3 and 0.031 mol Na2SO3 (a) What is the pH of the solution? (b) Write the net ionic equation for the reaction that occurs when NaOH is added to this buffer. (c) Calculate the new pH after 10. mL of 1.0 M NaOH is added to the buffer solution. (d) Calculate the new pH after 10. mL of 1.0 M NaOH is added to 500. mL of pure water. (e) Explain why the pH of the water changed so much as compared to the pH of the buffer.

Explanation / Answer

1)

a)

for pH = 6.00

the corresponding Ka of carbonic acid = 4.6 x10^-7

pKa = -log Ka = -log(4.6 x10^-7) = 6.34

here buffer = H2CO3 + HCO3-

For acidic buffer

Henderson-Hasselbalch equation

pH = pKa + log[salt/acid]

6 = 6.34 + log[HCO3-/H2CO3]

log[HCO3-/H2CO3] = -0.34

[HCO3-/H2CO3] = 0.457

b)

for pH = 8.00

the corresponding Ka of dihydrogen phosphate = 6.2 x10^-8

pKa = -log Ka = -log(6.2 x10^-8) = 7.21

here buffer = H2PO4- + HPO4-2

pH = pKa + log[salt/acid]

8 = 7.21 + log[HPO4-2/H2PO4-]

log[HPO4-2/H2PO4-] = 0.79

[HPO4-2/H2PO4-] = 6.165

c)

for pH = 11.00

the corresponding Ka of monohydrogen phosphate = 4.8 x10^-13

pKa = -log Ka = -log( 4.8 x10^-13) = 12.32

here buffer = HPO4-2 + PO4-3

pH = pKa + log[salt/acid]

11 =12.32 + log[PO4-3/HPO4-2]

log[PO4-3/HPO4-2] = -1.32

[PO4-3/HPO4-2] =0.0478

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