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Chem V01B Buffer and Titration Homework
1. What is the pH of a buffer that is 0.300 M HC2H3O2 and 0.300 M NaC2H3O2
given Ka for HC2H3O2 = 1.8 x 10-5
2. What is the pH of a buffer that is 0.300 M HC2H3O2 and 0.250 M NaC2H3O2
given Ka for HC2H3O2 = 1.8 x 10-5
3. What is the pH of a buffer that is 0.250 M HC2H3O2 and 0.300 M NaC2H3O2
given Ka for HC2H3O2 = 1.8 x 10-5
4. What is the pH of a buffer that has 0.300 mol HC2H3O2 and 0.300 mol
NaC2H3O2 in 1.00 L that has 0.020 mol NaOH added to it?
5. Compare the effect on pH of adding 0.020 mol NaOH to a buffer that has
0.200 mol HC2H3O2 and 0.200 mol NaC2H3O2 in 1.00 L to adding 0.020 mol
NaOH to 1.00 L of pure water? (pKa for HC2H3O2 = 4.745)
6. You have two buffers and to these buffers you add 0.010 mole of NaOH
Buffer 1
0.50 mol HC2H3O2 & 0.50 mol C2H3O2 Initial pH = 5.00
Buffer 2
0.050 mol HC2H3O2 & 0.050 mol C2H3O2 Initial pH = 5.00
a. Calculate the pH before adding the NaOH to each buffer
b. Calculate the pH after the NaOH to each buffer
c. Calculate the percentage change in the pH of each buffer
d. Which is the best buffer?
7. You have four weak acids HA
Chlorous Acid, HClO2
Nitrous Acid, HNO2
Formic Acid, HCHO2
Hypochlorous Acid, HClO
pKa = 1.95
pKa = 3.34
pKa = 3.74
pKa = 7.54
a. Which would be the best acid for making a buffer at pH = 7.0 ?
b. What ratio will you need [A-]/[HA] to be to obtain the correct pH?
8. A 10.0 mL sample of 0.300 M HNO2 is titrated with 0.200 M KOH.
a.
b.
c.
d.
e.
f.
Calculate the pH before any base is added
Calculate the volume of base needed to reach the equivalence point
Calculate the volume of base needed to reach the half equivalence point
Calculate the pH at the half equivalence point
Calculate the pH at the equivalence point
Calculate the pH when 20 mL of base is added