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Practice Test - Advanced Acid-Base Equilibrium


Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
 

 1. 
What is the effect of adding 10 mL of 0.1 M NaOH(aq) to 100 mL of 0.2 M NH4+(aq)?
1.
The pH will decrease.
2.
The concentration of NH3 will increase.
3.
The concentration of NH4+ will decrease.
a.
1 only
b.
2 only
c.
3 only
d.
2 and 3
e.
1, 2, and 3
 

 2. 
What is the pH of a solution that results from adding 25 mL of 0.15 M HCl to 25 mL of 0.52 M NH3? (Kb of NH3 = 1.8 x 10-5)
a.
2.74
b.
4.35
c.
9.65
d.
11.26
e.
11.41
 

 3. 
What is the pH of a solution that results from adding 25 mL of 0.50 M NaOH to 75 mL of 0.50 M CH3CO2H? (Ka of CH3CO2H = 1.8 x 10-5)
a.
2.67
b.
3.17
c.
4.44
d.
5.04
e.
5.35
 

 4. 
What is the pH of an aqueous solution of 0.30 M HF and 0.15 M F-? (Ka of HF = 7.2 x 10-4)
a.
1.83
b.
2.84
c.
3.14
d.
3.44
e.
10.86
 

 5. 
What is the pH of an aqueous solution containing 0.50 M CO32- and 0.20 M HCO3-? (Kb of CO32- = 2.1 x 10-4)
a.
3.28
b.
3.68
c.
10.32
d.
10.72
e.
12.01
 

 6. 
Which of the following combinations would be the best to buffer an aqueous solution at a pH of 5.0?
a.
H3PO4 and H2PO4-, Ka1 = 7.5 x 10-3
b.
HNO2 and NO2-, Ka = 4.5 x 10-4
c.
CH3CO2H and CH3COO-, Ka = 1.8 x 10-5
d.
H2PO4- and HPO42-, Ka2 = 6.2 x 10-8
e.
NH4+ and NH3, Ka = 5.7 x 10-10
 

 7. 
What is the pH of the buffer that results when 4.0 g of NH3 and 8.0 g of NH4Cl are diluted with water to a volume of 0.50 L? (Ka of NH4+ = 5.6 x 10-10)
a.
8.95
b.
9.06
c.
9.25
d.
9.45
e.
9.55
 

 8. 
What is the pH of the buffer that results when 11 g of NaCH3CO2 is mixed with 85 mL of 1.0 M CH3CO2H and diluted with water to 1.0 L? (Ka of CH3CO2H = 1.8 x 10-5)
a.
2.91
b.
3.86
c.
4.55
d.
4.74
e.
4.94
 

 9. 
What is the pH of the buffer that results when 12.5 g of NaH2PO4 and 22.0 g Na2HPO4 are mixed and diluted with water to 0.500 L? (The acid dissociation constants for phosphoric acid are Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8, and Ka3 = 3.6 x 10-13)
a.
2.30
b.
7.04
c.
7.38
d.
12.27
e.
12.62
 

 10. 
What is the pH of a buffer that results when 0.50 mole of Na3PO4 is mixed with 0.75 mole of HCl and diluted with water to 1.00 L? (The acid dissociation constants for phosphoric acid are Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8, and Ka3 = 3.6 x 10-13)
a.
7.03
b.
7.21
c.
7.38
d.
12.27
e.
12.44
 

 11. 
What mass of solid KF (molar mass = 58.1 g/mol) should be added to 2.0 L of 0.25 M HF to make a buffer with a pH of 3.14? (pKa for HF = 3.14)
a.
7.3 g
b.
15 g
c.
29 g
d.
58 g
e.
120 g
 

 12. 
The Ka of hypochlorous acid, HClO, is 3.5 x 10-8. What [ClO-]/[HClO] ratio is necessary to make a buffer with a pH of 7.71?
a.
2.0 x 10-8
b.
0.25
c.
0.56
d.
1.8
e.
3.9
 

 13. 
A buffer is prepared by combining 250 mL of 0.25 M NaOH and 250 mL of a 0.600 M weak acid, HA. If the pH of the buffer is 6.33, what is the pKa of the acid?
a.
5.95
b.
6.18
c.
6.33
d.
6.48
e.
6.71
 

 14. 
A buffer is composed of 0.250 mol H2PO4- and 0.250 mol HPO42- diluted with water to a volume of 1.00 L. The pH of the buffer is 7.210. How many moles of NaOH must be added to increase the pH to 8.210?
a.
0.045 mol
b.
0.125 mol
c.
0.205 mol
d.
0.250 mol
e.
0.500 mol
 

 15. 
A buffer contains 1.0 mol CH3CO2H and 1.0 mol CH3CO2- diluted with water to 1.0 L. How many moles of NaOH are required to increase the pH of the buffer to 5.10? (pKa of CH3CO2H = 4.74)
a.
0.36 mol
b.
0.39 mol
c.
0.44 mol
d.
0.61 mol
e.
0.64 mol
 

 16. 
What volume of 0.50 M NaOH should be added to 2.0 L of 0.25 M HCO3- to make a buffer with a pH of 10.02? (pKa of HCO3- = 10.32)
a.
0.17 mL
b.
83 mL
c.
2.5 x 102 mL
d.
3.3 x 102 mL
e.
5.0 x 102 mL
 

 17. 
A volume of 25.0 mL of 0.100 M HCO2H(aq) is titrated with 0.100 M NaOH(aq). What is the pH after the addition of 12.5 mL of NaOH? (Ka for HCO2H = 1.8 x 10-4)
a.
2.52
b.
3.74
c.
4.74
d.
7.00
e.
10.26
 

 18. 
A 25.0 mL sample of 0.200 M HClO(aq) is titrated with 0.250 M NaOH(aq). What is the pH of a solution when 85.0% of the acid is titrated? (Ka of HClO = 3.5 x 10-8)
a.
6.70
b.
7.39
c.
7.46
d.
7.55
e.
8.21
 

 19. 
A 25.0 mL sample of 0.0200 M NH3(aq) is titrated with 0.0100 M HCl(aq). What is the pH at the equivalence point? (Kb of NH3 = 1.8 x 10-5)
a.
3.46
b.
5.48
c.
5.72
d.
8.25
e.
10.54
 

 20. 
A 50.0 mL sample of 0.0240 M NH3(aq) is titrated with aqueous hydrochloric acid. What is the pH after the addition of 15.0 mL of 0.0600 M HCl(aq)? (Kb of NH3 = 1.8 x 10-5)
a.
8.78
b.
8.86
c.
9.25
d.
9.38
e.
9.73
 

 21. 
A 20.0 mL sample of 0.20 M sodium acetate is titrated with 0.11 M HCl(aq). What is the pH after the addition of 50.0 mL HCl(aq)? (Kb of CH3CO2- = 5.6 x 10-10)
a.
1.10
b.
1.67
c.
2.82
d.
9.11
e.
9.51
 

 22. 
Potassium hydrogen phthalate (molar mass = 204.2 g/mol) is used to standardize sodium hydroxide. If 26.37 mL of NaOH(aq) is required to titrate 0.7719 g KHP to the equivalence point, what is the concentration of the NaOH(aq)?

HC8H4O4-(aq) + OH-(aq) ⇌ C8H4O42-(aq) + H2O(l)
a.
0.02036 M
b.
0.02937 M
c.
0.09968 M
d.
0.1433 M
e.
5.977 M
 

 23. 
A 50.0 mL sample of vinegar is titrated with 0.774 M NaOH(aq). If the titration requires 41.6 mL of NaOH(aq), what is the concentration of acetic acid in the vinegar?
a.
0.0921 M
b.
0.429 M
c.
0.644 M
d.
0.930 M
e.
0.967 M
 

 24. 
An impure sample of sodium carbonate, Na2CO3, is titrated with 0.150 M HCl according to the reaction below.

2 HCl(aq) + Na2CO3(aq) ⇌  CO2(g) + H2O(l) + 2 NaCl(aq)

What is the percent of Na2CO3 in a 0.927 g sample if the titration requires 27.3 mL of HCl? The molar mass of Na2CO3 is 106.0 g/mol.
a.
0.221%
b.
23.4%
c.
46.8%
d.
93.7%
e.
104%
 

 25. 
Which is the best colored indicator to use in the titration of 0.0010 M CH3CO2-(aq) with HCl(aq)? Why? (Kb of CH3CO2- = 5.6 x 10-10)

Indicator
p K a
Bromocresol green
4.7
Phenol Red
7.8
Phenolphthalein
9.0
a.
Bromocresol green. The pH at the equivalence point is less than 7.0.
b.
Phenol Red. The pKb of acetate ion and the pKb of the indicator are similar.
c.
Phenol Red. The equivalence point of an acid-base titration occurs at a pH of 7.0.
d.
Phenolphthalein. The pKb of acetate ion and the pKb of the indicator are similar.
e.
Phenolphthalein. The pH at the equivalence point is greater than 7.0.
 



 
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