Chemistry The Molecular Nature of Matter

Neil D. Jespersen, James E. Brady, Frederick A. Senese

Chapter 16

Acids and Bases, A Molecular Look - all with Video Answers

Educators

Chapter Questions

Problem 1

How is a Bronsted acid defined? How is a Bronsted base defined?

Crystal Wang

Crystal Wang

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Problem 2

How are the formulas of the members of a conjugate acidbase pair related to each other? Within the pair, how can you tell which is the acid?

Crystal Wang

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Problem 3

Is $\mathrm{H}_{2} \mathrm{SO}_{4}$ the conjugate acid of $\mathrm{SO}_{4}^{2-}$ ? Explain your answer.

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Problem 4

What is meant by the term amphoteric? Give two chemical equations that illustrate the amphoteric nature of water.

Shahina -

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Problem 5

Define the term amphiprotic.

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Problem 6

Within the periodic table, how do the strengths of the binary acids vary from left to right across a period? How do they vary from top to bottom within a group?

David Collins

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Problem 7

Astatine, atomic number 85 , is radioactive and does not occur in appreciable amounts in nature. On the basis of what you have learned in this chapter, answer the following.
(a) How would the acid strength of HAt compare with that of HI?
(b) How would the acid strength of $\mathrm{HAtO}_{3}$ compare with that of $\mathrm{HBrO}_{3}$ ?

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Problem 8

Explain why nitric acid is a stronger acid than nitrous acid.

Crystal Wang

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Problem 9

Explain why $\mathrm{H}_{2} \mathrm{~S}$ is a stronger acid than $\mathrm{H}_{2} \mathrm{O}$.

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Problem 10

Which is the stronger Brønsted-Lowry base, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}$ or $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~S}^{-}$ ? What is the basis for your selection?

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Problem 11

Explain why $\mathrm{HClO}_{4}$ is a stronger acid than $\mathrm{H}_{2} \mathrm{SeO}_{4}$.

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Problem 12

The position of equilibrium in the equation below lies far to the left. Identify the conjugate acid-base pairs. Which of the two acids is stronger?
$$\mathrm{HOCl}(a q)+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{OCl}^{-}(a q)$$

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Problem 13

Consider the following: $\mathrm{CO}_{3}^{2-}$ is a weaker base than hydroxide ion, and $\mathrm{HCO}_{3}^{-}$ is a stronger acid than water. In the equation below, would the position of equilibrium lie to the left or to the right? Justify your answer.
$$\mathrm{CO}_{3}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{HCO}_{3}^{-}(a q)+\mathrm{OH}^{-}(a q)$$

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Problem 14

Acetic acid, $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$, is a weaker acid than nitrous acid, $\mathrm{HNO}_{2}$. How do the strengths of the bases $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}$ and $\mathrm{NO}_{2}^{-}$ compare?

Crystal Wang

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Problem 15

Nitric acid, $\mathrm{HNO}_{3}$, is a very strong acid. It is $100 \%$ ionized in water. In the reaction below, would the position of equilibrium lie to the left or to the right?
$$\mathrm{NO}_{3}^{-}(a q)+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{HNO}_{3}(a q)+\mathrm{OH}^{-}(a q)$$

Shahina -

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Problem 16

$ \mathrm{HClO}_{4}$ is a stronger proton donor than $\mathrm{HNO}_{3}$, but in water both acids appear to be of equal strength; they are both $100 \%$ ionized. Why is this so? What solvent property would be necessary in order to distinguish between the acidities of these two Brønsted-Lowry acids?

David Collins

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Problem 17

Formic acid, $\mathrm{HCHO}_{2}$, and acetic acid, $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$, are classified as weak acids, but in water $\mathrm{HCHO}_{2}$ is more fully ionized than $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$. However, if we use liquid ammonia as a solvent for these acids, they both appear to be of equal strengths; both are $100 \%$ ionized in liquid ammonia. Explain why this is so.

David Collins

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Problem 18

Which of the molecules below is expected to be the stronger Brønsted-Lowry acid? Why?

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Problem 19

Which of the molecules below has the stronger conjugate base? Explain your choice.

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Problem 20

Define Lewis acid and Lewis base.

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Problem 21

Explain why the addition of a proton to a water molecule to give $\mathrm{H}_{3} \mathrm{O}^{+}$ is a Lewis acid-base reaction.

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Problem 22

Methylamine has the formula $\mathrm{CH}_{3} \mathrm{NH}_{2}$ and the structure Use Lewis structures to illustrate the reaction of methylamine with boron trifluoride.

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Problem 23

Use Lewis structures to show the Lewis acid-base reaction between $\mathrm{SO}_{3}$ and $\mathrm{H}_{2} \mathrm{O}$ to give $\mathrm{H}_{2} \mathrm{SO}_{4} .$ Identify the Lewis acid and the Lewis base in the reaction.

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Problem 24

Explain why the oxide ion, $\mathrm{O}^{2-}$, can function as a Lewis base but not as a Lewis acid.

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Problem 25

The molecule $\mathrm{SbF}_{5}$ is able to function as a Lewis acid. Explain why it is able to be a Lewis acid.

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Problem 26

In the reaction of calcium with oxygen to form calcium oxide, each calcium gives a pair of electrons to an oxygen atom. Why isn't this viewed as a Lewis acid-base reaction?

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Problem 27

Suppose that a new element was discovered. Based on the discussions in this chapter, what properties (both physical and chemical) might be used to classify the element as a metal or a nonmetal?

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Problem 28

If the oxide of an element dissolves in water to give an acidic solution, is the element more likely to be a metal or a nonmetal?

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Problem 29

Boric acid is very poisonous and is used in ant bait (to kill ant colonies) and to poison cockroaches. It is a weak acid with a formula often written as $\mathrm{H}_{3} \mathrm{BO}_{3}$, although it is better written as $\mathrm{B}(\mathrm{OH})_{3} .$ It functions not as a BronstedLowry acid, but as a Lewis acid. Using Lewis structures, show how $\mathrm{B}(\mathrm{OH})_{3}$ can bind to a water molecule and cause the resulting product to be a weak Brønsted acid.

Crystal Wang

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Problem 30

Many chromium salts crystallize as hydrates containing the ion $\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+} .$ Solutions of these salts tend to be acidic. Explain why.

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Problem 31

Which ion is expected to give the more acidic solution, $\mathrm{Fe}^{2+}$ or $\mathrm{Fe}^{3+}$ ? Why?

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Problem 32

Ions of the alkali metals have little effect on the acidity of a solution. Why?

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Problem 33

What acid is formed when the following oxides react with water?
(a) $\mathrm{SO}_{3}$
(b) $\mathrm{CO}_{2}$
(c) $\mathrm{P}_{4} \mathrm{O}_{10}$

Shahina -

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Problem 34

Consider the following oxides: $\mathrm{CrO}, \mathrm{Cr}_{2} \mathrm{O}_{3}, \mathrm{CrO}_{3}$.
(a) Which is most acidic?
(b) Which is most basic?
(c) Which is most likely to be amphoteric?

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Problem 35

Write equations for the reaction of $\mathrm{Al}_{2} \mathrm{O}_{3}$ with
(a) a strong acid, and
(b) a strong base.

Shahina -

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Problem 36

Write the formula for the conjugate acid of each of the following.
(a) $\mathrm{F}^{-}$
(c) $\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}$
(e) $\mathrm{HCrO}_{4}^{-}$
(b) $\mathrm{N}_{2} \mathrm{H}_{4}$
(d) $\mathrm{O}_{2}^{2-}$

Crystal Wang

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Problem 37

Write the formula for the conjugate base of each of the following.
(a) $\mathrm{NH}_{2} \mathrm{OH}$
(c) HCN
(e) $\mathrm{HNO}_{2}$
(b) $\mathrm{HSO}_{3}^{-}$
(d) $\mathrm{H}_{5} \mathrm{IO}_{6}$

Crystal Wang

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Problem 38

Identify the conjugate acid-base pairs in the following reactions.
(a) $\mathrm{HNO}_{3}+\mathrm{N}_{2} \mathrm{H}_{4} \rightleftharpoons \mathrm{NO}_{3}^{-}+\mathrm{N}_{2} \mathrm{H}_{5}+$
(b) $\mathrm{NH}_{3}+\mathrm{N}_{2} \mathrm{H}_{5}{ }^{+} \rightleftharpoons \mathrm{NH}_{4}^{+}+\mathrm{N}_{2} \mathrm{H}_{4}$
(c) $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}+\mathrm{CO}_{3}{ }^{2-} \rightleftharpoons \mathrm{HPO}_{4}{ }^{2-}+\mathrm{HCO}_{3}^{-}$
(d) $\mathrm{HIO}_{3}+\mathrm{HC}_{2} \mathrm{O}_{4}^{-} \rightleftharpoons \mathrm{IO}_{3}^{-}+\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$

Shahina -

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Problem 39

Identify the conjugate acid-base pairs in the following reactions.
(a) $\mathrm{HSO}_{4}^{-}+\mathrm{SO}_{3}^{2-} \rightleftharpoons \mathrm{HSO}_{3}^{-}+\mathrm{SO}_{4}^{2-}$
(b) $\mathrm{S}^{2-}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{HS}^{-}+\mathrm{OH}^{-}$
(c) $\mathrm{CN}^{-}+\mathrm{H}_{3} \mathrm{O}^{+} \rightleftharpoons \mathrm{HCN}+\mathrm{H}_{2} \mathrm{O}$
(d) $\mathrm{H}_{2} \mathrm{Se}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{HSe}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}$

Shahina -

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Problem 40

Choose the stronger acid: (a) $\mathrm{HBr}$ or $\mathrm{HCl}$; (b) $\mathrm{H}_{2} \mathrm{O}$ or $\mathrm{HF} ;$ (c) $\mathrm{H}_{2} \mathrm{~S}$ or HBr. Give your reasons.

Shahina -

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Problem 41

Choose the stronger acid: (a) $\mathrm{H}_{2} \mathrm{~S}$ or $\mathrm{H}_{2} \mathrm{Se} ;$ (b) $\mathrm{H}_{2} \mathrm{Te}$ or $\mathrm{HI} ;$ (c) $\mathrm{PH}_{3}$ or $\mathrm{NH}_{3}$. Give your reasons.

Shahina -

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Problem 42

Choose the stronger acid and give your reason:
(a) $\mathrm{HOCl}$ or $\mathrm{HClO}_{2}$;
(b) $\mathrm{H}_{2} \mathrm{SeO}_{4}$ or $\mathrm{H}_{2} \mathrm{SeO}_{3}$.

Shahina -

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Problem 43

Choose the stronger acid: (a) $\mathrm{HIO}_{3}$ or $\mathrm{HIO}_{4}$; (b) $\mathrm{H}_{3} \mathrm{AsO}_{4}$ or $\mathrm{H}_{3} \mathrm{As} \mathrm{O}_{3}$. Give your reasons.

Crystal Wang

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Problem 44

Choose the stronger acid: (a) $\mathrm{HClO}_{3}$ or $\mathrm{HIO}_{3}$; (b) $\mathrm{HIO}_{2}$ or $\mathrm{HClO}_{3} ;$ (c) $\mathrm{H}_{2} \mathrm{SeO}_{3}$ or $\mathrm{HBrO}_{4 \cdot}$ Give your reasons.

Shahina -

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Problem 45

Choose the stronger acid:
(a) $\mathrm{H}_{3} \mathrm{AsO}_{4}$ or $\mathrm{H}_{3} \mathrm{PO}_{4}$;
(b) $\mathrm{H}_{2} \mathrm{CO}_{3}$ or $\mathrm{HNO}_{3}$;
(c) $\mathrm{H}_{2} \mathrm{SeO}_{4}$ or $\mathrm{HClO}_{4} \cdot$ Give your
reasons.

Shahina -

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Problem 46

The ion $\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+}$ is weakly acidic. Write an equation showing its behavior as a Brønsted-Lowry acid in water.

David Collins

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Problem 47

The compound $\mathrm{Mg}(\mathrm{OH})_{2}$ is basic, but $\mathrm{Si}(\mathrm{OH})_{4}$ is an acid (silicic acid). Why?

Shahina -

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Problem 48

Use Lewis symbols to diagram the reaction
$$\mathrm{NH}_{2}^{-}+\mathrm{H}^{+} \longrightarrow \mathrm{NH}_{3}$$
Identify the Lewis acid and Lewis base in the reaction.

Shahina -

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Problem 49

Use Lewis symbols to diagram the reaction
$$\mathrm{BF}_{3}+\mathrm{F}^{-} \longrightarrow \mathrm{BF}_{4}-$$
Identify the Lewis acid and Lewis base in the reaction.

Crystal Wang

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Problem 50

Beryllium chloride, $\mathrm{BeCl}_{2}$, exists in the solid as a polymer composed of long chains of $\mathrm{BeCl}_{2}$ units arranged as follows. The formula of the chain can be represented as $\left(\mathrm{BeCl}_{2}\right)_{n}$ where $n$ is a large number. Use Lewis structures to show how the reaction $n \mathrm{BeCl}_{2} \longrightarrow\left(\mathrm{BeCl}_{2}\right)_{n}$ is a Lewis acidbase reaction.

David Collins

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Problem 51

Aluminum chloride, $\mathrm{AlCl}_{3}$, forms molecules with itself with the formula $\mathrm{Al}_{2} \mathrm{Cl}_{6}$. Its structure is Use Lewis structures to show how the reaction $2 \mathrm{AlCl}_{3} \longrightarrow \mathrm{Al}_{2} \mathrm{Cl}_{6}$ is a Lewis acid-base reaction.

David Collins

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Problem 52

Use Lewis structures to diagram the reaction
$$\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}$$
Identify the Lewis acid and Lewis base in this reaction.

Shahina -

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Problem 53

Use Lewis structures to diagram the reaction
$$\mathrm{CO}_{2}+\mathrm{O}^{2-} \longrightarrow \mathrm{CO}_{3}^{2-}$$
Identify the Lewis acid and Lewis base in this reaction.

Shahina -

Numerade Educator

Problem 54

Use Lewis structures to show how the following reaction can be viewed as the displacement of one Lewis base by another Lewis base from a Lewis acid. Identify the two Lewis bases and the Lewis acid.
$$\mathrm{NH}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{NH}_{3}+\mathrm{OH}^{-}$$

David Collins

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Problem 55

Use Lewis structures to show how the following reaction involves the transfer of a Lewis base from one Lewis acid to another. Identify the two Lewis acids and the Lewis base.
$$\mathrm{CO}_{3}^{2-}+\mathrm{SO}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{SO}_{3}^{2-}$$

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Problem 56

What is the formula of the conjugate acid of dimethylamine, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}$ ? What is the formula of its conjugate base?

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Problem 57

Using liquid ammonia as a solvent, sodium amide reacts with ammonium chloride in an acid-base neutralization reaction. Assuming that these compounds are completely dissociated in liquid ammonia, write molecular, ionic, and net ionic equations for the reaction. Which substance is the acid and which is the base?

David Collins

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Problem 58

In liquid $\mathrm{SO}_{2}$ as a solvent, $\mathrm{SOCl}_{2}$ reacts with $\mathrm{Na}_{2} \mathrm{SO}_{3}$ in a reaction that can be classified as neutralization (acid plus base yields solvent plus a salt). Write an equation for the reaction. Which solute is the acid and which is the base? Describe what is happening in terms of the Lewis definition of acids and bases.

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Problem 59

The following space-filling model depicts the structure of a compound called ethanamide.
How would you expect its base strength to compare with that of ammonia? Justify your answer.

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Problem 60

Which of the following compounds is the stronger base? Explain.

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Problem 61

Which of the two molecules below is the stronger Bronsted-Lowry acid? Why?

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Problem 62

Write equations that illustrate the amphiprotic nature of the bicarbonate ion.

Sima Sarker

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Problem 63

Hydrogen peroxide is a stronger Brønsted-Lowry acid than water.
(a) Explain why this is so.
(b) Is an aqueous solution of hydrogen peroxide acidic or basic?

Shahina -

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Problem 64

Sodium hydroxide, $\mathrm{NaOH}$, is basic. Aluminum hydroxide, $\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3}(\mathrm{OH})_{3}$, is amphoteric. The compound $\mathrm{O}_{3} \mathrm{ClOH}$ (usually written $\mathrm{HClO}_{4}$ ) is acidic. Considering that each compound contains one or more OH groups, why are their acid-base properties so different?

David Collins

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Problem 65

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$, is a weaker Brønsted-Lowry base than ammonia. In the following reaction, would the position of equilibrium lie to the left or to the right? Justify your answer.
$$\mathrm{N}_{2} \mathrm{H}_{5}{ }^{+}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{N}_{2} \mathrm{H}_{4}+\mathrm{NH}_{4}{ }^{+}$$

David Collins

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Problem 66

Identify the two Bronsted-Lowry acids and two bases in the reaction
$$\mathrm{NH}_{2} \mathrm{OH}+\mathrm{CH}_{3} \mathrm{NH}_{3}+\rightleftharpoons \mathrm{NH}_{3} \mathrm{OH}^{+}+\mathrm{CH}_{3} \mathrm{NH}_{2}$$

Crystal Wang

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Problem 67

In the reaction in the preceding exercise, the position of equilibrium lies to left. Identify the stronger acid in each of the conjugate pairs in the reaction.

David Collins

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Problem 68

How would you expect the degree of ionization of $\mathrm{HClO}_{3}$ to compare in the solvents $\mathrm{H}_{2} \mathrm{O}(I)$ and $\mathrm{HF}(l) ?$
The reactions are
$$\begin{aligned}\mathrm{HClO}_{3}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{ClO}_{3}^{-} \\
\mathrm{HClO}_{3}+\mathrm{HF} \rightleftharpoons \mathrm{H}_{2} \mathrm{~F}^{+}+\mathrm{ClO}_{3}^{-}
\end{aligned}$$
Justify your answer.

Crystal Wang

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Problem 69

On the basis of the VSEPR theory, sketch the structure of the $\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{ }^{3+}$ ion. Sketch the two possible structures of the ion formed when a proton is removed from four of the six water molecules. Which is the more likely of the two structures?

Crystal Wang

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Problem 70

A mixture is prepared containing $0.10 M$ of each of the following: arsenic acid, sodium arsenate, arsenous acid, and sodium arsenite. What are the formulas and chemical structures of the predominant arsenic-containing species present in the solution at equilibrium? Write the equation for the equilibrium.

David Collins

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Problem 71

Are all Arrhenius acids Bronsted-Lowry acids? Are they all Lewis acids? Give examples if they are not. Give a reasoned explanation if they are.

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Problem 72

How could you determine whether $\mathrm{HBr}$ is a stronger acid than HI?

Shahina -

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Problem 73

Alcohols are organic compounds that have an $-\mathrm{OH}$ group. Are alcohols acids or bases? Sugars have an OH group on almost every carbon atom; are they acids or bases? Phenol is a benzene ring with an $-\mathrm{OH}$ group. Is phenol an acid or base?

Crystal Wang

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Problem 74

Acid rain, acid mine runoff, and acid leaching of metals from soils are important environmental considerations. What do these topics refer to and how do they affect you as a person?

Shahina -

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