Chemistry, The Central Science, 10th edition

Theodore L. Brown; H. Eugene LeMay, Jr.;and Bruce E. Bursten

Chapter 16Acid-Base Equilibria

Troy WoodUniversity of BuffaloBuffalo, NY 2006, Prentice Hall

Is NH3 an acid, base, or could it be both?

1. Acid

2. Base

3. Both

Correct Answer:

In this chapter we learned that a more general definition for a base is a substance that can accept another proton, which is true for NH3 because of the lone electron pair on the N atom.

1. Acid

2. Base

3. Both

Is H2O an acid, base, or could it be both?

1. Acid

2. Base

3. Both

Correct Answer:

As indicated in the equilibrium below, water is an amphoteric substance that can either accept another proton or donate a proton.

OHH

H OHH

OHH+ H+

+

_

1. Acid

2. Base

3. Both

Is the ion PO43 an acid, base, or could it

be both?

-P

O

-O

O-

O- P

O-

-O

O-

O+

1. Acid

2. Base

3. Both

Correct Answer:

Phosphate is a proton acceptor, regardless of which resonance structure is being considered.

1. Acid

2. Base

3. Both

-P

O

-O

O-

O- P

O-

-O

O-

O+

What is the approximate pH of an aqueous solution of 1 1012 M HCl?

1. 22. 7 3. 124. 145. None of the above

Correct Answer:

This is an aqueous solution, therefore water will autoionize. The concentration of protons due to autoionization of water will dominate that of such a dilute strong acid.

1. 22. 7 3. 124. 145. None of the above

What is [H+] in an aqueous solution whose pH = 3.72?

1. 1.9 103 M2. 5.1 103 M3. 1.9 104 M4. 5.1 104 M5. 5.1 1010 M

Correct Answer:

3.72 = log[H+]

3.72 = log[H+]

[H+] = 1.9 10 4 M

1. 1.9 103 M2. 5.1 103 M3. 1.9 104 M4. 5.1 104 M5. 5.1 1010 M

What is the pH of an aqueous solution of [OH] = 6.0 103 M?

1. 2.222. 3.223. 7.004. 10.785. 11.78

Correct Answer:

There is more than one method to solve this problem. One is presented below:

pOH = log(6.0 103)

= 2.22

pH = 14.00 pOH

= 14.00 2.22

= 11.78

1. 2.222. 3.223. 7.004. 10.785. 11.78

The [H+] in an 0.020 M solution of HNO2 is 3.0 103 M. What is the Ka of HNO2?

1. 4.5 104

2. 6.0 105

3. 9.0 106

4. 1.5 101 5. None of the

above

N

OHO

nitrous acid

Correct Answer:

[HA]

]][A[H

aK

0.020

109.0

0.020

]10[3.0 623

aK

4104.5 aK

1. 4.5 104

• 6.0 105

• 9.0 106

• 1.5 101 • None of the

above

The pH of a 0.050 M weak acid is 3.00. What is the percentage ionization?

1. 0.10%2. 0.20% 3. 1.0%4. 2.0%5. 3.0%

Correct Answer:

100%[HA]

][Hionization %

eq

o

100%[0.050]

]10[1.0ionization %

-3

2.0%ionization %

Since pH = 3.00,

[H+] = 1.0 103 M, so 1. 0.10%2. 0.20% 3. 1.0%4. 2.0%5. 3.0%

For a certain weak acid, Ka = 2.0 105. What is Kb for its conjugate base?

1. 4.5 103

2. 5.0 103

3. 1.0 109

4. 4.0 1010

5. 5.0 1010

Correct Answer:

wba KKK

a

wb K

KK

10

5-

-14

105.0102.0

101.0

bK

1. 4.5 103

2. 5.0 103

3. 1.0 109

4. 4.0 1010

5. 5.0 1010

Which of the following oxyacid species is the strongest acid?

1. HClO2. HClO2

3. HClO3

4. HClO4

Correct Answer:

For oxyacids that have the same central atom Y, acid strength increases as the number of O atoms bound to Y increases.

Thus, HClO4 is the strongest acid of this series.

1. HClO2. HClO2

3. HClO3

4. HClO4