Chemistry 106, Chapter 14 Exercises
pH of Buffered Solutions
1. Calculate the pH of a buffer that is 0.12 M in lactic acid (Ka = 1.4 x 10-4) and 0.11 M in sodium
lactate. ans. 3.82
2. A solution is made by mixing 30. mL of 0.15 M CH3COOH (Ka =1.8 x 10-5) with 70. mL of 0.20 M
CH3COONa. Calculate the pH of this solution. ans. 5.24
3. Calculate the pH of a buffer formed by mixing 85. mL of 0.13 M lactic acid (Ka = 1.4 x 10-4) with
95 mL of 0.15 M sodium lactate. ans. 3.96
4. 20.0 g of CH3COOH (Ka = 1.8 x 10-5) and 20.0 g of CH3COONa are dissolved in 2.00 L of solution.
Find the pH. What effect does adding water have on the pH? ans. 4.60, no effect.
Preparing Buffered Solutions
5. What is the ratio of HCO3 to H2CO3 (Ka = 4.3 x 10-7) in blood of pH 7.4? ans. 11
6. What is the ratio of HCO3- to H2CO3 in a marathon runner whose blood pH is 7.1? ans. 5.4
7. How many moles of NaBrO should be added to 1.00L of 0.050M HBrO (Ka = 2.5 x 10-9) to form a
buffer solution of pH 9.15? ans. 0.18 mole
8. How many grams of NaC3H5O3 (112.0 g/mole) should be added to 1.00L of 0.150 M HC3H5O3 (Ka
= 1.4 x 10-4) to form a buffer solution with pH = 2.90? ans. 1.87 g
9. How many grams of NaCHO2 (68.0 g/mole) must be added to 350. mL of 0.159 M HCHO2 (Ka =
1.9 x 10-4) to form a buffer solution with a pH = 3.0? ans. 0.72 g
10. A buffer made from NaHCO3 and Na2CO3 is prepared with a pH of 9.40.
a. What must the [CO32-] /[HCO3-] ratio be? Ka for HCO3- is 4.7 x 10-11. ans. 0.118
b. How many moles of NaHCO3 must be added to a liter of 0.225 M Na2CO3 to give this pH?
ans. 1.9 mol
c. How many grams of Na2CO3 must be added to 475. mL of 0.336 M NaHCO3 to give this pH?
ans. 2.0g
d. What volume of 0.200M NaHCO3 must be added to 735. mL of a 0.139 M solution of Na2CO3 to
give this pH? ans. 4.3L
Adding Strong Acid or Strong Base to a Buffered Solution
11. A buffer contains 0.10 mol CH3COOH (Ka = 1.8 x 10-5) and 0.13 mole CH3COONa in 1.00L.
a. What's the pH? ans. 4.86
b. What's the pH after the addition of 0.02 mole KOH? ans. 5.0
c. What's the pH after the addition of 0.02 mole HNO3? ans. 4.71
12. A buffer contains 0.12 mole propionic acid, HC3H5O2 (Ka = 1.3 x 10-5) and 0.10 mol NaC3H5O2.
a. What's the pH? ans. 4.81
b. What's the pH after the addition of 25.0 mL of 0.40 M KOH? ans. 4.89
c. What's the pH after the addition of 25.0 mL of 0.40 M HI? ans. 4.73
13. 250 mL of buffer has a concentration of 0.20 M nicotinic acid, HNic (Ka = 1.4 x 10-5) and 0.15 M
Nic-.
a. What's the pH? ans. 4.73
b. What's the pH after the addition of 30 mL of 0.15 M NaOH? ans. 4.82
c. What's the pH after the addition of 30 mL of 0.15 M HClO4? ans. 4.64
Neutralization Reactions
14. Complete and balance the following reaction. Give the molecular and net ionic equations.
NaOH + HCl
Ba(OH)2 + HNO3
Sr(OH)2 + HI
HC2H3O2 + NaOH
HF + KOH
H2CO3 + Ca(OH)2
Al(OH)3 + HCl
Mg(OH)2 +HCl
NH3 + HCl
KClO + HBr
NaHCO3 + HNO3
Titrations
15. A 0.20 M solution of KOH is used to titrate 35.00 mL of 0.25 M HBr.
a. What volume of KOH is required to reach the equivalence point? ans. 43.8 mL
b. What's the pH before any KOH is added? ans. 0.60
c. What's the pH halfway to the equivalence point? ans. 1.11
d. What's the pH of the solution at the equivalence point? ans. 7.0
16. A 0.35 M solution of HNO3 is used to titrate 50.00 mL of 0.30 M NaOH.
a. What volume of HNO3 is required to reach the equivalence point? ans. 42.9 mL
b. What's the pH before any HNO3 is added? ans. 13.48
c. What's the pH halfway to the equivalence point? ans. 13.02
d. What's the pH of the solution at the equivalence point? ans. 7.0
17. A 0.40 M solution of KOH is used to titrate 25.00 mL of 0.50 M benzoic acid (Ka = 6.6 x 10-5).
a. What volume of KOH is required to reach the equivalence point? ans. 31.25 mL
b. What's the pH before any KOH is added? ans. 2.24
c. What's the pH halfway to the equivalence point? ans. 4.18
d. What's the pH of the solution at the equivalence point? ans. 8.76
18. A 0.12 M solution of HCl is used to titrate 50.00 mL of 0.10 M sodium lactate (Kb = 7.1 x 10-11).
a. What volume of HCl is required to reach the equivalence point? ans. 41.67 mL
b. What's the pH before any HCl is added? ans. 8.43
c. What's the pH halfway to the equivalence point? ans. 3.85
d. What's the pH of the solution at the equivalence point? ans. 2.57
19. A 0.20 M solution of NaOH is used to titrate 25.00 mL of 0.35 M acetic acid (Ka = 1.8 x 10-5).
a. What volume of NaOH is required to reach the equivalence point? ans. 43.75mL
b. What is the pH before any NaOH is added? ans. 2.60
c. What is the pH at the mid point of the titration? ans. 4.74
d. What is the pH of the solution at the equivalence point? ans. 8.92
Answers to Exercise 14
NaOH + HCl → NaCl + H2O
Ba(OH)2 + 2HNO3 → Ba(NO3)2 + 2H2O
Sr(OH)2 + 2HI → SrI2 + 2H2O
H+ + OH- → H2O
H+ + OH- → H2O
H+ + OH- → H2O
HC2H3O2 + NaOH → NaC2H3O2 + H2O
HF + KOH → KF + H2O
H2CO3 + Ca(OH)2 → CaCO3(s) + 2H2O
HC2H3O2 + OH- → C2H3O2- + H2O
HF + OH- → F- + H2O
H2CO3 + Ca2+ + 2OH- → CaCO3(s) + 2H2O
Al(OH)3 + 3HCl → AlCl3 + 3H2O
Mg(OH)2 +2HCl → MgCl2 + 2H2O
NH3 + HCl → NH4+ + ClKClO + HBr → HClO + KBr
NaHCO3 + HNO3 → H2CO3 + NaNO3
Al(OH)3 + 3H+ → Al3+ + 3H2O
Mg(OH)2 +2H+ → Mg2+ + 2H2O
NH3 + H+ → NH4+
ClO- + H+ → HClO
HCO3- + H+ → H2CO3