Chapter 16: Acids and Bases

Question 1

What is the Arrhenius definition of an acid?

Answer 1

A substance that produces H+ ions in aqueous solution.

Question 2

What is the Arrhenius definition of a base?

Answer 2

A substance that produces OH- ions in aqueous solution.

Question 3

What does the strength of an acid or a base depend on?

Answer 3

The extent of the electrolyte’s dissociation into its component ions.

Question 4

What is a strong acid?

Answer 4

An acid that completely dissociates (ionizes) in solution.

Question 5

What is a weak acid?

Answer 5

An acid that partially dissociates (ionizes) in solution.

Question 6

What is a strong base?

Answer 6

A base that completely dissociates (ionizes) in solution.

Question 7

What is a weak base?

Answer 7

A base that partially dissociates (ionizes) in solution.

Question 8

What is the Bronsted-Lowry definition of an acid?

Answer 8

A proton (H+) donor.

Question 9

What is the Bronsted-Lowry definition of a base?

Answer 9

A proton (H+) acceptor.

Question 10

What are amphoteric substances?

Answer 10

Substances that can act as acids or bases.

Question 11

What is a conjugate acid-base pair?

Answer 11

Two substances related to each other by the transfer of a proton.

Question 12

What is a conjugate acid?

Answer 12

Any base to which a proton has been added.

Question 13

What is a conjugate base?

Answer 13

Any acid from which a proton has been removed.

Question 14

What are the factors of a molecule that affect the ease with which a hydrogen is donated (and therefore makes the molecule acidic)?

Answer 14

1. The polarity of the bond
2. The strength of the bond

Question 15

In order for HY to be acidic, the H–Y bond must be what?

Answer 15

The H–Y bond must be polarized with the hydrogen atom as the positive pole because hydrogen must be lost from the acid as a positively charged ion. A partial positive charge on the hydrogen atom facilitates its loss.

Question 16

Why isn’t LiH acidic?

Answer 16

It is ionic with the negative charge on the hydrogen atom. (H is more electronegative than Li)

Question 17

Why isn’t the C–H bond acidic?

Answer 17

It is virtually nonpolar because the electronegativities of carbon and hydrogen are similar; therefore, C–H is not acidic.

Question 18

Why is the H–F bond acidic?

Answer 18

The H–F bond is polar with the positive charge on the hydrogen atom.

Question 19

How does the strength of the H–Y bond relate to the strength of an acid? Why?

Answer 19

The stronger the H–Y bond, the weaker the acid. The more tightly the hydrogen atom is held, the less likely it is to come off.

Question 20

Why are HCl and HBr strong acids but HF is not?

Answer 20

HCl and HBr have weaker bonds. HF, in contrast, has a stronger bond and is therefore a weak acid, despite the greater bond polarity of HF.

Question 21

In oxyacids, what determines the ease with which the H is donated?

Answer 21

The ease with which the H is donated is related to the strength and polarity of the H–O bond. The factors affecting the strength and polarity of the bond are the electronegativity of the element Y and the number of oxygen atoms attached to the element Y.

Question 22

As Y becomes more electronegative, how does this affect the H–O bond of an oxyacid?

Answer 22

The more electronegative the element Y is, the more it weakens and polarizes the H–O bond and the more acidic the oxyacid is.

Question 23

How does the number of oxygen atoms bonded to Y affect the strength of the acid?

Answer 23

The greater the number of oxygen atoms bonded to Y, the stronger the acid.

Question 24

What are the six strong acids given in the book?

Answer 24

1. HCl (hydrochloric acid)
2. HBr (hydrobromic acid)
3. HI (hydroiodic acid)
4. HNO3 (nitric acid)
5. HClO4 (perchloric acid)
6. H2SO4 (sulfuric acid)

Question 25

Why is HCl a strong acid but HF is not?

Answer 25

The strength of the HF bond relative to the HCl bond makes HF less likely to ionize in solution than HCl.

Question 26

What is the acid ionization constant (Ka)?

Answer 26

The equilibrium constant for the ionization reaction of the weak acid in water. It is a way to quantify the relative strength of a weak acid.

Question 27

What is the autoionization of water?

Answer 27

When water acts as an acid and a base with itself. Given by the reaction: H2O <=> H+ + OH-

Question 28

What is the ion product constant of water?

Answer 28

[H+][OH-] = 10^-14 at 25˚ C

Question 29

How is pH defined?

Answer 29

pH is the negative of the log of the hydronium ion concentration. pH = -log[H3O+]

Question 30

How is pOH defined?

Answer 30

pOH = -log[OH-]

Question 31

How are pH and pOH related to each other?

Answer 31

They add to 14.00 at 25˚ C.

Question 32

How is pKa defined?

Answer 32

pKa = -log(Ka)

Question 33

How is pKa used to quantify the strength of an acid?

Answer 33

The smaller the pKa, the stronger the acid.

Question 34

In a solution containing a strong or weak acid, what are the two potential sources of H3O+?

Answer 34

1. The ionization of the acid 2. The autoionization of water

Question 35

What is the percent ionization of a weak acid?

Answer 35

The ratio of the ionized acid concentration to the initial acid concentration, multiplied by 100%.

Question 36

How is the equilibrium H3O+ concentration of a weak acid related to its initial concentration?

Answer 36

The equilibrium H+ concentration increases with increasing initial concentration of the acid.

Question 37

How is the percent ionization of a weak acid related to its concentration?

Answer 37

The percent ionization of a weak acid decreases with increasing concentration of the acid.

Question 38

When a strong acid and a weak acid are in solution, what effect does the strong acid have on the weak acid?

Answer 38

The H+ formed by the strong acid suppresses the formation of additional H+ by the weak acid or the autoionization of water.

Question 39

What is the base ionization constant (Kb)?

Answer 39

The extent of ionization of a weak base in solution. Given by: Kb = [BH+][OH-]/[B]

Question 40

An anion that is the conjugate base of a weak acid is what?

Answer 40

A weak base.

Question 41

An anion that is the conjugate base of a strong acid is what?

Answer 41

pH-neutral (forms solutions that are neither acidic nor basic)

Question 42

How is the strength of an acid related to the strength of its conjugate base?

Answer 42

The weaker the acid, the stronger the conjugate base.

Question 43

pKa + pKb = ?

Answer 43

14

Question 44

How do anions and cations factor into acid-base reactions?

Answer 44

Anions can sometimes act as weak bases. Cation can sometimes act as weak acids.

Question 45

In general, cations that are the counterions of strong bases are what?

Answer 45

pH-neutral. For example, Na+, K+, and Ca2+ are the counterions of the strong bases NaOH, KOH, and Ca(OH)2 and are therefore themselves pH-neutral.

Question 46

In general, a cation that is the conjugate acid of a weak base is what?

Answer 46

A weak acid.

Question 47

What effect do small, highly charged metal cations have in solution?

Answer 47

Cations such as Al3+ and Fe3+ form weakly acidic solutions.

Question 48

What is the definition of a Lewis acid?

Answer 48

An electron pair acceptor.

Question 49

What is the definition of a Lewis base?

Answer 49

An electron pair donor.