Harris QCA 8e Chapter 08
1. Which of the following pairs of compounds and ions could be used to form a
buffer solution?
(a) 0.10 M HCl and 0.10 M NaCl
(b) 0.10 M NH4Cl and 0.10 M NH3
(c) 0.10 M HNO2 and 1.0 x 10-4 M NaNO2
2. Which of the combination of ions and molecules may produce a buffer solution in
an aqueous environment?
(a) 50.00 mL of 0.100 M NaOH and 50.00 mL of 0.100 M CH 3COOH
(b) 50.00 mL of 0.100 M HNO3 and 50.00 mL of 0.100 M CH3COOH
(c) 50.0 mL of 0.050 M HNO3 and 50.0 mL of 0.100 M CH3COONa
3. Calculate the ratio of ethyl amine (CH3CH2NH2) to the ethyl ammonium ion
(CH3CH2NH3+) in a solution with a pH of 11.0. pKa for CH3CH2NH3+ = 10.636.
(a) 2.31
(b) 10.81
(c) 0.432
4. A buffer solution was prepared by mixing 50.0 mL of a 0.100 M solution of
CH3COOH with 0.500 grams of NaCH3COO. The resulting mixture is diluted to 100.0
mL. What is the pH of the solution? Ka for acetic acid is 1.75 x 10-5.
(a) 4.84
(b) 7.67
(c) 4.97
5. How many grams of NaCH3COO must be added to 150.0 mL of a 0.150 M solution
of CH3COOH to produce a buffer of pH 4.75? Assume that the volume will remain
constant, pKa for CH3COOH = 4.757
(a) 0.147 molar
(b) 12.1 grams
(c) 1.81 grams
6. A buffer solution was prepared by dissolving 5.00 grams of sodium propanate
(NaCH3CH2CO2) in a solution containing 0.100 moles of propanoic acid (CH3CH2CO2H)
and diluting the mixture to 500.0 mL. To this solution was added 5.00 mL of 1.00 M
HCl. Calculate the pH of the resulting solution. pKa for propanoic acid is 4.874.
(a) 4.65
(b) 4.62
(c) 4.52
7. A beaker containing 500.0 mL was determined to contain 0.150 M ammonia
(NH3) and 0.150 M ammonium chloride NH4Cl. To this solution was added 50.0 mL of
0.15 M HCl. What was the change in pH of the ammonia-ammonium ion solution?
pKa for NH4+ = 9.244.
(a) The pH of the solution will go down 0.087 pH units.
(b) The pH of the solution will go up 0.13 pH units.
(c) The pH of the solution will go up 0.087 pH units.
8. How many mL of 0.100 M HCl should be added to 500.0 mL of 0.150 M sodium
acetate (NaCH3CO2) to produce a buffer pH 5.0? pKa acetic acid = 4.757.
(a) 273 mL
(b) 1000 mL
(c) 476 mL
9. Using the acid dissociation constant table in your textbook, which buffer system
will give the greatest buffer capacity at pH 5.0?
(a) chlorous acid/chlorite ion
(b) hydrogen cyanide/cyanide ion
(c) propanoic acid
10. An indicator may be selected for an acid-base application based on the pH range
where the indicator changes color. A chemist wanted an indicator to change color
between pH 5.8 and 6.1. The following compounds were available for selection: In a
Ka = 1.5 X 10-3, Inb Ka = 1.3 X 10-6, and Inc Ka = 1.8 X 10-8. Which would be the
proper indicator to select?
(a) Ina
(b) Inb
(c) Inc
11. How many grams of NaOH must be added to 1.50 L of a 0.400 M solution of
oxoacetic acid (HCOCO2H) to produce a buffer pH 4.00? pKa for oxoacetic acid =
3.46.
(a) 18.67 grams
(b) 0.47 grams
(c) 5.33 grams
12. What is the Ka of 0.0450 M HA, if the measured pH is 5.78?
(a) 6.12 x 10-11molar
(b) 1.66 x 10-6 molar
(c) 3.69 x 10-5 molar
13. If one measures the equilibrium constant for each of the following solutions,
which relationship is correct?
A - mix CH2CH2CH2CH2COOH with CH2CH2CH2NH2
B - mix HNO3 with CsOH
C - mix KOH with HCOOH
(a) K for A > K for B > K for C
(b) K for C > K for A > K for B
(c) K for B > K for C > K for A
14. Calculate the pH of a solution prepared by dissolving 0.0775 mol acetic acid
(HCOOH) and 0.0460 mol sodium acetate (HCOONa) in 1 L of water. The Ka of acetic
acid is 1.77 x 10-4.
(a) 3.107
(b) 3.525
(c) 3.752
15. A solution prepared by dissolving 0.0775 mol acetic acid (HCOOH) and 0.0460
mol sodium acetate (HCOONa) in 1 L of water. What is the pH if 0.0100 mol of KOH
is added to the solution. The Ka of acetic acid is 1.77 x 10-4.
(a) 3.107
(b) 3.525
(c) 3.671
16. What weight of sodium lactate (CH3CHOHCOONa; MW = 112.05) must be added
to 500 mL of 0.200 M lactic acid (CH3CHOHCOOH, MW= 90.07; Ka = 1.4 X 10-4) in
order to produce a buffered solution with a pH = 4.50?
(a) 4.03 grams
(b) 50.09 grams
(c) 100.2 grams