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Chemistry

Steven S. Zumdahl, Susan A. Zumdahls

Chapter 20

The Representative Elements: Groups 5A Through 8A - all with Video Answers

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Chapter Questions

01:27

Problem 1

Elemental nitrogen exists as $\mathrm{N}_{2}$, whereas in the gas phase the elements phosphorus, arsenic, and antimony consist of $\mathrm{P}_{4}, \mathrm{As}_{4}$, and $\mathrm{Sb}_{4}$ molecules, respectively. Give a possible reason for this difference between $\mathrm{N}_{2}$ and the other group $5 \mathrm{~A}$ elements.

Anand Jangid
Anand Jangid
Numerade Educator
02:54

Problem 2

What is nitrogen fixation? Give some examples of nitrogen fixation.

LJ
Lena Jake
Numerade Educator
01:00

Problem 3

In large doses, selenium is toxic. However, in moderate intake, selenium is a physiologically important element. How is selenium physiologically important?

LJ
Lena Jake
Numerade Educator
01:37

Problem 4

Ozone is a possible replacement for chlorine in municipal water purification. Unlike chlorine, virtually no ozone remains after treatment. This has good and bad consequences. Explain.

LJ
Lena Jake
Numerade Educator
01:19

Problem 5

Sulfur forms a wide variety of compounds in which it has $+6$, $+4,+2,0$, and $-2$ oxidation states. Give examples of sulfur compounds having each of these oxidation states.

Ronald Prasad
Ronald Prasad
Numerade Educator
01:17

Problem 6

When a halogen is a central atom in a compound, the compound typically is $s p^{3}, d s p^{3}$, or $d^{2} s p^{3}$ hybridized. Using bromine as your central atom, give example compounds for each type of hybridization. What is the molecular structure for each of your examples?

Anand Jangid
Anand Jangid
Numerade Educator
01:22

Problem 7

Explain the following observations regarding reactions of halogens.
a. In the hydrogen-chlorine cannon lecture demonstration, a lit magnesium strip is held to a mixture of $\mathrm{H}_{2}$ and $\mathrm{Cl}_{2}$, resulting in a reaction that sends the stopper to the cannon flying across the lecture room.
b. When a brown bromine solution is added dropwise to an organic compound called an alkene, the brown color disappears, resulting in a colorless reaction mixture.
c. When aluminum is reacted with iodine, the reaction container emits sparks and a deep purple colored smoke.

Anand Jangid
Anand Jangid
Numerade Educator
01:21

Problem 8

There is evidence that radon reacts with fluorine to form compounds similar to those formed by xenon and fluorine. Predict the formulas of these $\operatorname{RaF}_{x}$ compounds. Why is the chemistry of r

Anand Jangid
Anand Jangid
Numerade Educator
02:41

Problem 9

The oxyanion of nitrogen in which it has the highest oxidation state is the nitrate ion $\left(\mathrm{NO}_{3}^{-}\right)$. The corresponding oxyanion of phosphorus is $\mathrm{PO}_{4}{ }^{3-}$. The $\mathrm{NO}_{4}{ }^{3-}$ ion is known but not very stable. The $\mathrm{PO}_{3}^{-}$ ion is not known. Account for these differences in terms of the bonding in the four anions.

Aadit Sharma
Aadit Sharma
Numerade Educator
09:26

Problem 10

In each of the following pairs of substances, one is stable and known, and the other is unstable. For each pair, choose the stable substance, and explain why the other is unstable.
a. $\mathrm{NF}_{5}$ or $\mathrm{PF}_{5}$
b. $\mathrm{AsF}_{5}$ or $\mathrm{AsI}_{5}$
c. $\mathrm{NF}_{3}$ or $\mathrm{NBr}_{3}$

Matthew Bittner
Matthew Bittner
Numerade Educator
02:16

Problem 11

Several important compounds contain only nitrogen and oxygen. Place the following compounds in order of increasing mass percent of nitrogen.
a. NO, a gas formed by the reaction of $\mathrm{N}_{2}$ with $\mathrm{O}_{2}$ in internal combustion engines
b. $\mathrm{NO}_{2}$, a brown gas mainly responsible for the brownish colon of photochemical smog
c. $\mathrm{N}_{2} \mathrm{O}_{4}$, a colorless liquid used as fuel in space shuttles
d. $\mathrm{N}_{2} \mathrm{O}$, a colorless gas sometimes used as an anesthetic by dentists (known as laughing gas)

Anand Jangid
Anand Jangid
Numerade Educator
04:17

Problem 12

Nitric acid is produced commercially by the Ostwald process, represented by the following equations:
$$
\begin{aligned}
4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(g) & \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\
2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{NO}_{2}(g) \\
3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(I) & \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g)
\end{aligned}
$$
What mass of $\mathrm{NH}_{3}$ must be used to produce $1.0 \times 10^{6} \mathrm{~kg} \mathrm{HNO}_{3}$ by the Ostwald process? Assume $100 \%$ yield in each reaction and assume that the NO produced in the third step is not recycled.

Stephen Ho
Stephen Ho
Numerade Educator
01:21

Problem 13

Complete and balance each of the following reactions.
a. the decomposition of solid ammonium nitrate
b. the decomposition of gaseous dinitrogen pentoxide
c. the reaction between solid potassium phosphide and water
d. the reaction between liquid phosphorus tribromide and water
e. the reaction between aqueous ammonia and aqueous sodium hypochlorite

Anand Jangid
Anand Jangid
Numerade Educator
03:50

Problem 14

Arsenic reacts with oxygen to form oxides that react with water in a manner analogous to that of the phosphorus oxides. Write balanced chemical equations describing the reaction of arsenic with oxygen and the reaction of the resulting oxide with water.

LJ
Lena Jake
Numerade Educator
01:45

Problem 15

Phosphorus occurs naturally in the form of fluorapatite, $\mathrm{CaF}_{2}$. $3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$, where the dot indicates 1 part $\mathrm{CaF}_{2}$ to 3 parts $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$. This mineral is reacted with an aqueous solution of sulfuric acid in the preparation of a fertilizer. The products are phosphoric acid, hydrogen fluoride, and gypsum, $\mathrm{CaSO}_{4}$. $2 \mathrm{H}_{2} \mathrm{O}$. Write and balance the chemical equation describing this process.

Anand Jangid
Anand Jangid
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01:08

Problem 16

Lewis structures can be used to understand why some molecules react in certain ways. Write the Lewis structure for the reactants and products in the reactions described below.
a. Nitrogen dioxide dimerizes to produce dinitrogen tetroxide.
b. Boron trihydride accepts a pair of electrons from ammonia, forming $\mathrm{BH}_{3} \mathrm{NH}_{3}$.
Give a possible explanation for why these two reactions occur.

Anand Jangid
Anand Jangid
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01:54

Problem 17

Air bags are activated when a severe impact causes a steel ball to compress a spring and electrically ignite a detonator cap. This causes sodium azide $\left(\mathrm{NaN}_{5}\right)$ to decompose explosively according to the following reaction:
$$
2 \mathrm{NaN}_{3}(s) \longrightarrow 2 \mathrm{Na}(s)+3 \mathrm{~N}_{2}(g)
$$
How many moles of $\mathrm{NaN}_{3}(s)$ must be reacted to inflate an air bag to $70.0 \mathrm{~L}$ at STP?

Lijeesh Krishnan
Lijeesh Krishnan
Numerade Educator
05:03

Problem 18

Urea $\left(\mathrm{H}_{2} \mathrm{NCONH}_{2}\right)$ is used extensively as a nitrogen source in fertilizers. It is produced commercially from the reaction of ammonia and carbon dioxide:
$$
2 \mathrm{NH}_{3}(g)+\mathrm{CO}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{NCONH}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(g)
$$
Ammonia gas at $223^{\circ} \mathrm{C}$ and $90 .$ atm flows into a reactor at a rate of $500 .$ Lmin. Carbon dioxide at $223^{\circ} \mathrm{C}$ and 45 atm flows into the reactor at a rate of $600 . \mathrm{L} / \mathrm{min} .$ What mass of urea is produced per minute by this reaction assuming a $100 \%$ yield?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:26

Problem 19

Hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is used as a fuel in liquid-fueled rockets. When hydrazine reacts with oxygen gas, nitrogen gas and water vapor are produced. Write a balanced equation and use bond energies from Table $8.4$ to estimate $\Delta H$ for this reaction.

Julian Taurozzi
Julian Taurozzi
Numerade Educator
04:01

Problem 20

The space shuttle orbiter utilizes the oxidation of methylhydrazine by dinitrogen tetroxide for propulsion:
$4 \mathrm{~N}_{2} \mathrm{H}_{3} \mathrm{CH}_{3}(l)+5 \mathrm{~N}_{2} \mathrm{O}_{4}(l) \longrightarrow 12 \mathrm{H}_{2} \mathrm{O}(g)+9 \mathrm{~N}_{2}(g)+4 \mathrm{CO}_{2}(g)$
Calculate $\Delta H^{\circ}$ for this reaction using data in Appendix $4 .$ Compare your answer to the $\Delta H$ value determined in Sample Exercise 20.2. Explain any discrepancies.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
08:59

Problem 21

Many oxides of nitrogen have positive values for the standard free energy of formation. Using NO as an example, explain why this is the case.

Michaelle Lubich
Michaelle Lubich
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05:45

Problem 22

Using data from Appendix 4 calculate $\Delta H^{\circ}, \Delta S^{\circ}$, and $\Delta G^{\circ}$ for the reaction
$$
\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g)
$$
Why does NO form in an automobile engine but then does not readily decompose back to $\mathrm{N}_{2}$ and $\mathrm{O}_{2}$ in the atmosphere?

LJ
Lena Jake
Numerade Educator
20:46

Problem 23

Compare the Lewis structures with the molecular orbital view of the bonding in $\mathrm{NO}, \mathrm{NO}^{+}$, and $\mathrm{NO}^{-}$. Account for any discrepancies between the two models.

Matthew Bittner
Matthew Bittner
Numerade Educator
02:11

Problem 24

The energy to break a particular bond is not always constant. It takes about $200 \mathrm{~kJ} / \mathrm{mol}$ less energy to break the $\mathrm{N}-\mathrm{Cl}$ bond in NOCl as compared with $\mathrm{NCl}_{3}$ :
$$
\begin{array}{cl}
\mathrm{NOCl} \longrightarrow \mathrm{NO}+\mathrm{Cl} & \Delta H^{\circ}=158 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{NCl}_{3} \longrightarrow \mathrm{NCl}_{2}+\mathrm{Cl} & \Delta H^{\circ}=375 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
Why is there such a great discrepancy in the apparent $\mathrm{N}-\mathrm{Cl}$ bond energies? Hint: Consider what happens to the nitrogen-oxygen bond in the first reaction.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:59

Problem 25

Predict the relative acid strengths of the following compounds.
a. $\mathrm{H}_{3} \mathrm{PO}_{4}$ and $\mathrm{H}_{3} \mathrm{PO}_{3}$
b. $\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}$, and $\mathrm{HPO}_{4}^{2-}$

Anand Jangid
Anand Jangid
Numerade Educator
01:14

Problem 26

Trisodium phosphate (TSP) is an effective grease remover. Like many cleaners, TSP acts as a base in water. Write a balanced equation to account for this behavior.

Anand Jangid
Anand Jangid
Numerade Educator
01:31

Problem 27

Isohypophosphonic acid $\left(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{0}\right)$ and diphosphonic acid $\left(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{5}\right)$
are tri- and diprotic acids, respectively. Draw Lewis structures for these acids that are consistent with these facts.

Anand Jangid
Anand Jangid
Numerade Educator
08:43

Problem 28

One of the most strongly acidic solutions known is a mixture of antimony pentafluoride $\left(\mathrm{SbF}_{5}\right)$ and fluorosulfonic acid $\left(\mathrm{HSO}_{3} \mathrm{~F}\right)$. The dominant equilibria are
$$
\begin{aligned}
\mathrm{SbF}_{5}+\mathrm{HSO}_{3} \mathrm{~F} & \rightleftharpoons \mathrm{F}_{5} \mathrm{SbOSO}_{2} \mathrm{FH} \\
\mathrm{F}_{5} \mathrm{SbOSO}_{2} \mathrm{FH}+\mathrm{HSO}_{3} \mathrm{~F} & \rightleftharpoons \mathrm{H}_{2} \mathrm{SO}_{3} \mathrm{~F}^{+}+\mathrm{F}_{5} \mathrm{SbOSO}_{2} \mathrm{~F}^{-}
\end{aligned}
$$
a. Draw Lewis structures for all the species shown in the preceding reactions. Predict the hybridization of the central Sb and $\mathrm{S}$ atoms in each structure.
b. This superacid solution is capable of protonating (adding $\mathrm{H}^{+}$
to) virtually every known organic compound. What is the active protonating agent in the superacid solution?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:17

Problem 29

Use bond energies to estimate the maximum wavelength of light that will cause the reaction
$$
\mathrm{O}_{3} \stackrel{h \mathrm{O}}{\longrightarrow} \mathrm{O}_{2}+\mathrm{O}
$$

Anand Jangid
Anand Jangid
Numerade Educator
01:21

Problem 30

The xerographic (dry writing) process was invented in 1938 by C. Carlson. In xerography, an image is produced on a photoconductor by exposing it to light. Selenium is commonly used, since its conductivity increases three orders of magnitude upon exposure to light in the range from 400 to $500 \mathrm{~nm}$. What color light should be used to cause selenium to become conductive? (See Figure 7.2.)

LJ
Lena Jake
Numerade Educator
01:37

Problem 31

Complete and balance each of the following reactions.
a. the reaction between sulfur dioxide gas and oxygen gas
b. the reaction between sulfur trioxide gas and water
c. the reaction between aqueous sodium thiosulfate and aqueous iodine
d. the reaction between copper metal and aqueous hot sulfuric acid

Anand Jangid
Anand Jangid
Numerade Educator
00:59

Problem 32

Write a balanced equation describing the reduction of $\mathrm{H}_{2} \mathrm{SeO}_{4}$ by $\mathrm{SO}_{2}$ to produce selenium.

Aadit Sharma
Aadit Sharma
Numerade Educator
02:02

Problem 33

For each of the following, write the Lewis structure(s), predict the molecular structure (including bond angles), and give the expected hybridization of the central atom.
a. $\mathrm{SO}_{3}^{2-}$
c. $\mathrm{SCl}_{2}$
e. $\mathrm{TeF}_{6}$
b. $\mathrm{O}_{5}$
d. $\mathrm{SeBr}_{4}$

Anand Jangid
Anand Jangid
Numerade Educator
01:11

Problem 34

Disulfur dinitride $\left(\mathrm{S}_{2} \mathrm{~N}_{2}\right)$ exists as a ring of alternating sulfur and nitrogen atoms. $\mathrm{S}_{2} \mathrm{~N}_{2}$ will polymerize to polythiazyl, which acts as a metallic conductor of electricity along the polymer chain. Write a Lewis structure for $\mathrm{S}_{2} \mathrm{~N}_{2}$.

Anand Jangid
Anand Jangid
Numerade Educator
06:44

Problem 35

Hydrogen peroxide is used as a cleaning agent in the treatment of cuts and abrasions for several reasons. It is an oxidizing agent that can directly kill many microorganisms; it decomposes upon contact with blood, releasing elemental oxygen gas (which inhibits the growth of anaerobic microorganisms); and it foams upon contact with blood, which provides a cleansing action. In the laboratory, small quantities of hydrogen peroxide can be prepared by the action of an acid on an alkaline earth metal peroxide, such as barium peroxide:
$$
\mathrm{BaO}_{2}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}_{2}(a q)+\mathrm{BaCl}_{2}(a q)
$$
What mass of hydrogen peroxide should result when $1.50 \mathrm{~g}$ of barium peroxide is treated with $25.0 \mathrm{~mL}$ of hydrochloric acid soIution containing $0.0272 \mathrm{~g}$ of $\mathrm{HCl}$ per $\mathrm{mL}$ ? What mass of which reagent is left unreacted?

Julian Taurozzi
Julian Taurozzi
Numerade Educator
02:42

Problem 36

During the developing process of black-and-white film, silver bromide is removed from photographic film by the fixer. The major component of the fixer is sodium thiosulfate. The net ionic equation for the reaction is
$$
\mathrm{AgBr}(s)+2 \mathrm{~S}_{2} \mathrm{O}_{3}{ }^{2-}(a q) \longrightarrow \mathrm{Ag}\left(\mathrm{S}_{2} \mathrm{O}_{3}\right)_{2}{ }^{3-}(a q)+\mathrm{Br}^{-}(a q)
$$
What mass of $\mathrm{AgBr}$ can be dissolved by $1.00 \mathrm{~L}$ of $0.200 \mathrm{M}$ $\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3} ?$ (Assume the reaction goes to completion.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:13

Problem 37

Write the Lewis structure for $\mathrm{O}_{2} \mathrm{~F}_{2}$. Predict the bond angles and hybridization of the two central oxygen atoms. Assign oxidation states and formal charges to the atoms in $\mathrm{O}_{2} \mathrm{~F}_{2}$. The compound $\mathrm{O}_{2} \mathrm{~F}_{2}$ is a vigorous and potent oxidizing and fluorinating agent. Are oxidation states or formal charges more useful in accounting for these properties of $\mathrm{O}_{2} \mathrm{~F}_{2}$ ?

Aadit Sharma
Aadit Sharma
Numerade Educator
02:01

Problem 38

For each of the following, write the Lewis structure(s), predict the molecular structure (including bond angles), and give the expected hybridization of the central atom.
a. Freon- $12\left(\mathrm{CCl}_{2} \mathrm{~F}_{2}\right)$
c. iodine trichloride
b. perchloric acid
d. bromine pentafluoride

Anand Jangid
Anand Jangid
Numerade Educator
01:10

Problem 39

Complete and balance each of the following reactions.
a. $\mathrm{BaCl}_{2}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow$
b. $\mathrm{BrF}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow$
c. $\mathrm{SiO}_{2}(s)+\mathrm{HF}(a q) \longrightarrow$

Anand Jangid
Anand Jangid
Numerade Educator
04:32

Problem 40

Hypofluorous acid is the most recently prepared of the halogen oxyacids. Weighable amounts were first obtained in 1971 by M. $\mathrm{H}$. Studies and E. N. Appelman using the fluorination of ice. Hypofluorous acid is exceedingly unstable, decomposing spontaneously (with a half-life of $30 \mathrm{~min}$ ) to $\mathrm{HF}$ and $\mathrm{O}_{2}$ in a Teflon container at room temperature. It reacts rapidly with water to produce HF, $\mathrm{H}_{2} \mathrm{O}_{2}$, and $\mathrm{O}_{2}$. In dilute acid, $\mathrm{H}_{2} \mathrm{O}_{2}$ is the major product; in dilute base, $\mathrm{O}_{2}$ is the major product.
a. Write balanced equations for the reactions described above.
b. Assign oxidation states to the elements in hypofluorous acid. Does this suggest why hypofluorous acid is so unstable?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
03:55

Problem 41

Hydrazine is somewhat toxic. Use the following half-reactions to explain why household bleach (highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia.
$\mathrm{ClO}^{-}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{OH}^{-}+\mathrm{Cl}^{-} \quad 8^{\circ}=0.90 \mathrm{~V}$
$\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-} \quad 8^{\circ}=-0.10 \mathrm{~V}$

Julian Taurozzi
Julian Taurozzi
Numerade Educator
04:25

Problem 42

What is a disproportionation reaction? Use the following reduction potentials
$\mathrm{ClO}_{3}^{-}+3 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}_{2}+\mathrm{H}_{2} \mathrm{O} \quad \mathscr{8}^{*}=1.21 \mathrm{~V}$
$\mathrm{HClO}_{2}+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}+\mathrm{H}_{2} \mathrm{O} \quad \mathscr{8}^{*}=1.65 \mathrm{~V}$
to predict whether $\mathrm{HClO}_{2}$ will disproportionate.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
03:29

Problem 43

The xenon halides and oxides are isoelectronic with many other compounds and ions containing halogens. Give a molecule or ion in which iodine is the central atom that is isoelectronic with each of the following.
a. xenon tetroxide
d. xenon tetrafluoride
b. xenon trioxide
e. xenon hexafluoride
c. xenon difluoride

Aadit Sharma
Aadit Sharma
Numerade Educator
05:46

Problem 44

For each of the following, write the Lewis structure(s), predict the molecular structure (including bond angles), and give the expected hybridization of the central atom.
a. $\mathrm{KrF}_{2}$
b. $\mathrm{KrF}_{4}$
c. $\mathrm{XeO}_{2} \mathrm{~F}_{2}$
d. $\mathrm{XeO}_{2} \mathrm{~F}_{4}$

LJ
Lena Jake
Numerade Educator
01:25

Problem 45

Xenon difluoride has proven to be a versatile fluorinating agent. For example, in the reaction
$$\mathrm{C}_{6} \mathrm{H}_{6}(l)+\mathrm{XeF}_{2}(g) \longrightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~F}(l)+\mathrm{Xe}(g)+\mathrm{HF}(g)$$
the by-products Xe and HF are easily removed, leaving pure $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~F}$. Xenon difluoride is stored in an inert atmosphere free from oxygen and water. Why is this necessary?

Anand Jangid
Anand Jangid
Numerade Educator
05:58

Problem 46

Using the data in Table 20.12, calculate the mass of argon at $25^{\circ} \mathrm{C}$ and $1.0$ atm in a room $10.0 \mathrm{~m} \times 10.0 \mathrm{~m} \times 10.0 \mathrm{~m}$. How many $\mathrm{Ar}$
atoms are in this room? How many Ar atoms do you inhale in one breath (approximately $2 \mathrm{~L}$ ) of air at $25^{\circ} \mathrm{C}$ and $1.0 \mathrm{~atm}$ ? Argon gas is inert, so it poses no serious health risks. However, if significant amounts of radon were inhaled into the lungs, lung cancer is a possible result. Explain the health-risk differences between argon gas and radon gas.

Pam Owens
Pam Owens
Numerade Educator
01:40

Problem 47

Which do you think would be the greater health hazard, the release of a radioactive nuclide of Sr or a radioactive nuclide of Xe into the environment? Assume the amount of radioactivity is the same in each case. Explain your answer on the basis of the chemical properties of Sr and Xe. Why are the chemical properties of a radioactive substance important in assessing its potential health hazards?

Arron Martel
Arron Martel
Numerade Educator
17:32

Problem 48

The most significant source of natural radiation is radon-222. ${ }^{222} \mathrm{Rn}$, a decay product of ${ }^{238} \mathrm{U}$, is continuously generated in the earth's crust, allowing gaseous $\mathrm{Rn}$ to seep into the basements of buildings. Because ${ }^{222} \mathrm{Rn}$ is an $\alpha$ -particle producer with a relatively short half-life of $3.82$ days, it can cause biological damage when inhaled.
a. How many $\alpha$ particles and $\beta$ particles are produced when ${ }^{238} \mathrm{U}$ decays to ${ }^{222} \mathrm{Rn} ?$ What nucleus is produced when ${ }^{222} \mathrm{Rn}$ decays?
b. Radon is a noble gas so one would expect it to pass through the body quickly. Why is there a concern over inhaling ${ }^{222} \mathrm{Rn}$ ?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:06

Problem 49

The compound $\mathrm{NF}_{3}$ is quite stable, but $\mathrm{NCl}_{3}$ is very unstable $\left(\mathrm{NCl}_{3}\right.$ was first synthesized in 1811 by P. L. Dulong, who lost three fingers and an eye studying its properties). The compounds $\mathrm{NBr}_{3}$ and $\mathrm{NI}_{3}$ are rare, although the explosive compound $\mathrm{NI}_{3} \cdot \mathrm{NH}_{3}$ is known. Account for the instability of these halides of nitrogen.

Nicole Smina
Nicole Smina
Numerade Educator
02:11

Problem 50

The $\mathrm{N}_{2} \mathrm{O}$ molecule is linear and polar.
a. On the basis of this experimental evidence, which arrangement, NNO or NON, is correct? Explain your answer.
b. On the basis of your answer in part a, write the Lewis structure of $\mathrm{N}_{2} \mathrm{O}$ (including resonance forms). Give the formal charge on each atom and the hybridization of the central atom.
c. How would the multiple bonding in : $\mathrm{N} \equiv \mathrm{N}-\ddot{O}$ : be described in terms of orbitals?

David Collins
David Collins
Numerade Educator
04:57

Problem 51

Oxidation of the cyanide ion produces the stable cyanate ion, $\mathrm{OCN}^{-}$. The fulminate ion, $\mathrm{CNO}^{-}$, on the other hand, is very unstable. Fulminate salts explode when struck; $\mathrm{Hg}(\mathrm{CNO})_{2}$ is used in blasting caps. Write the Lewis structures and assign formal charges for the cyanate and fulminate ions. Why is the fulminate ion so unstable?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:06

Problem 52

Sodium bismuthate $\left(\mathrm{NaBiO}_{3}\right)$ is used to test for the presence of $\mathrm{Mn}^{2+}$ in solution by the following reaction:
$$\mathrm{Mn}^{2+}(a q)+\mathrm{NaBiO}_{3}(s) \longrightarrow \mathrm{MnO}_{4}^{-}(a q)+\mathrm{BiO}_{3}{ }^{3-}(a q)$$
a. Balance this equation.
b. Given that bismuth does not form double bonds with oxygen in $\mathrm{BiO}_{3}^{-}$ and that $\mathrm{NaBiO}_{3}$ is relatively insoluble in water, what type of structure must $\mathrm{NaBiO}_{3}$ have to account for this behavior?

Anand Jangid
Anand Jangid
Numerade Educator
06:02

Problem 53

Bacterial digestion is an economical method of sewage treatment. The reaction is an intermediate step in the conversion of the nitrogen in organic compounds into nitrate ions. How much bacterial tissue is produced in a treatment plant for every $1.0 \times 10^{4} \mathrm{~kg}$ of wastewater containing $3.0 \% \mathrm{NH}_{4}{ }^{+}$ ions by mass? Assume that $95 \%$ of the ammonium ions are consumed by the bacteria.

Julian Taurozzi
Julian Taurozzi
Numerade Educator
01:33

Problem 54

An unknown element is a nonmetal and has a valence electron configuration of $n s^{2} n p^{4}$.
a. How many valence electrons does this element have?
b. What are some possible identities for this element?
c. What is the formula of the compound this element would form with lithium?
d. Would this element have a larger or smaller radius than barium?
e. Would this element have a greater or smaller ionization energy than fluorine?

Anand Jangid
Anand Jangid
Numerade Educator
01:10

Problem 55

The structure of $\mathrm{TeF}_{5}^{-}$ is Draw a complete Lewis structure for $\mathrm{TeF}_{5}^{-}$, and explain the distortion from the ideal square pyramidal structure.

Anand Jangid
Anand Jangid
Numerade Educator
02:36

Problem 56

Photogray lenses contain small embedded crystals of solid silver chloride. Silver chloride is light-sensitive because of the reaction
$$\mathrm{AgCl}(s) \stackrel{h v}{\longrightarrow} \mathrm{Ag}(s)+\mathrm{Cl}$$
Small particles of metallic silver cause the lenses to darken. In the lenses this process is reversible. When the light is removed, the reverse reaction occurs. However, when pure white silver chloride is exposed to sunlight it darkens; the reverse reaction does not occur in the dark.
a. How do you explain this difference?
b. Photogray lenses do become permanently dark in time. How do you account for this?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:39

Problem 57

Ammonia is produced by the Haber process, in which nitrogen and hydrogen are reacted directly using an iron mesh impregnated with oxides as a catalyst. For the reaction
$$\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightleftharpoons 2 \mathrm{NH}_{3}(g)$$
equilibrium constants ( $K_{\mathrm{p}}$ values) as a function of temperature are $300^{\circ} \mathrm{C}, \quad 4.34 \times 10^{-3}$
$500^{\circ} \mathrm{C}, \quad 1.45 \times 10^{-5}$
$600^{\circ} \mathrm{C}, \quad 2.25 \times 10^{-6}$
Is the reaction exothermic or endothermic?

Julian Taurozzi
Julian Taurozzi
Numerade Educator
10:56

Problem 58

Phosphate buffers are important in regulating the $\mathrm{pH}$ of intracellular fluids at $\mathrm{pH}$ values generally between $7.1$ and $7.2 .$ What is the concentration ratio of $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}$ to $\mathrm{HPO}_{4}{ }^{2-}$ in intracellular fluid at $\mathrm{pH}=7.15$ ?
$\mathrm{H}_{2} \mathrm{PO}_{4}^{-}(a q) \rightleftharpoons \mathrm{HPO}_{4}{ }^{2-}(a q)+\mathrm{H}^{+}(a q) \quad K_{\mathrm{a}}=6.2 \times 10^{-8}$
Why is a buffer composed of $\mathrm{H}_{3} \mathrm{PO}_{4}$ and $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}$ ineffective in buffering the $\mathrm{pH}$ of intracellular fluid?
$$\mathrm{H}_{3} \mathrm{PO}_{4}(a q) \rightleftharpoons \mathrm{H}_{2} \mathrm{PO}_{4}^{-}(a q)+\mathrm{H}^{+}(a q) \quad K_{\mathrm{a}}=7.5 \times 10^{-3}$$

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:58

Problem 59

Commercial cold packs and hot packs are available for treating athletic injuries. Both types contain a pouch of water and a dry chemical. When the pack is struck, the pouch of water breaks, dissolving the chemical, and the solution becomes either hot or cold. Many hot packs use magnesium sulfate, and many cold packs use ammonium nitrate. Write reactions to show how these strong electrolytes break apart when they dissolve in water.

LJ
Lena Jake
Numerade Educator
01:38

Problem 60

Classify each of the following as a strong acid or a weak acid.

Ian Kaigh
Ian Kaigh
Numerade Educator
01:08

Problem 61

Consider the following Lewis structure where $\mathrm{E}$ is an unknown element:

Anand Jangid
Anand Jangid
Numerade Educator
00:39

Problem 62

Consider the following Lewis structure where $\mathrm{E}$ is an unknown element: What are some possible identities for element E? Predict the molecular structure (including bond angles) for this ion.

Lottie Adams
Lottie Adams
Numerade Educator
01:38

Problem 63

The unit cell for a pure xenon fluoride compound is shown below. What is the formula of the compound?

Madi Sousa
Madi Sousa
Numerade Educator
01:27

Problem 64

Many structures of phosphorus-containing compounds are drawn with some $\mathrm{P}=\mathrm{O}$ bonds. These bonds are not the typical $\pi$ bonds we've considered, which involve the overlap of two $p$ orbitals. Instead, they result from the overlap of a $d$ orbital on the phosphorus atom with a $p$ orbital on oxygen. This type of $\pi$ bonding is sometimes used as an explanation for why $\mathrm{H}_{3} \mathrm{PO}_{3}$ has the first structure below rather than the second:
Draw a picture showing how a $d$ orbital and a $p$ orbital overlap to form a $\pi$ bond.

Christina Lollar
Christina Lollar
Numerade Educator
01:10

Problem 65

Use bond energies (Table $8.4$ ) to show that the preferred products for the decomposition of $\mathrm{N}_{2} \mathrm{O}_{3}$ are $\mathrm{NO}_{2}$ and $\mathrm{NO}$ rather than $\mathrm{O}_{2}$ and $\mathrm{N}_{2} \mathrm{O} .$ (The $\mathrm{N}-\mathrm{O}$ single bond energy is $201 \mathrm{~kJ} / \mathrm{mol}$.)

Anand Jangid
Anand Jangid
Numerade Educator
04:40

Problem 66

Sodium tripolyphosphate $\left(\mathrm{Na}_{5} \mathrm{P}_{3} \mathrm{O}_{10}\right)$ is used in many synthetic detergents to soften the water by complexing $\mathrm{Mg}^{2+}$ and $\mathrm{Ca}^{2+}$ ions. It also increases the efficiency of surfactants (wetting agents) that lower a liquid's surface tension. The $K$ value for the formation of $\mathrm{MgP}_{3} \mathrm{O}_{10}{ }^{3-}$ is $4.0 \times 10^{8}$. The reaction is
$$\mathrm{Mg}^{2+}+\mathrm{P}_{3} \mathrm{O}_{10}{ }^{5-} \leftrightharpoons \mathrm{MgP}_{3} \mathrm{O}_{10}{ }^{3-}$$
Calculate the concentration of $\mathrm{Mg}^{2+}$ in a solution that was originally 50. ppm of $\mathrm{Mg}^{2+}\left(50 . \mathrm{mg} / \mathrm{L}\right.$ of solution) after $40 . \mathrm{g} \mathrm{Na}_{5} \mathrm{P}_{3} \mathrm{O}_{10}$
is added to $1.0 \mathrm{~L}$ of the solution.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
12:14

Problem 67

One pathway for the destruction of ozone in the upper atmosphere is a. Which species is a catalyst?
b. Which species is an intermediate?
c. The activation energy $E_{a}$ for the uncatalyzed reaction $$
\mathrm{O}_{3}(g)+\mathrm{O}(g) \longrightarrow 2 \mathrm{O}_{2}(g)$$
is $14.0 \mathrm{~kJ} . E_{\mathrm{a}}$ for the same reaction when catalyzed by the presence of $\mathrm{NO}$ is $11.9 \mathrm{~kJ} .$ What is the ratio of the rate constant for the catalyzed reaction to that for the uncatalyzed reaction at $25^{\circ} \mathrm{C}$ ? Assume that the frequency factor $A$ is the same for each reaction.
d. One of the concerns about the use of Freons is that they will migrate to the upper atmosphere, where chlorine atoms can be generated by the reaction
Chlorine atoms also can act as a catalyst for the destruction of ozone. The first step of a proposed mechanism for chlorinecatalyzed ozone destruction is
Assuming a two-step mechanism, propose the second step in the mechanism and give the overall balanced equation.
e. The activation energy for Cl-catalyzed destruction of ozone is 2.1 $\mathrm{kJ} / \mathrm{mol}$. Estimate the efficiency with which $\mathrm{Cl}$ atoms destroy ozone as compared with NO molecules at $25^{\circ} \mathrm{C}$. Assume that the frequency factor $A$ is the same for each catalyzed reaction and assume similar rate laws for each catalyzed reaction.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
05:03

Problem 68

Using data from Appendix 4 , calculate $\Delta H^{\circ}, \Delta G^{\circ}$, and $K_{\mathrm{p}}$ (at 298
K) for the production of ozone from oxygen:
$$3 \mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{O}_{3}(g)$$
At $30 \mathrm{~km}$ above the surface of the earth, the temperature is about
230. $\mathrm{K}$, and the partial pressure of oxygen is about $1.0 \times 10^{-3}$ atm. Estimate the partial pressure of ozone in equilibrium with oxygen at $30 \mathrm{~km}$ above the earth's surface. Is it reasonable to assume that the equilibrium between oxygen and ozone is maintained under these conditions? Explain.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:00

Problem 69

You travel to a distant, cold planet where the ammonia flows like water. In fact, the inhabitants of this planet use ammonia (an abundant liquid on their planet) much as earthlings use water. Ammonia is also similar to water in that it is amphoteric and undergoes autoionization. The $K$ value for the autoionization of ammonia is $1.8 \times 10^{-12}$ at the standard temperature of the planet. What is the $\mathrm{pH}$ of ammonia at this temperature?

Aadit Sharma
Aadit Sharma
Numerade Educator
03:56

Problem 70

Nitrogen gas reacts with hydrogen gas to form ammonia gas. You have an equimolar mixture of nitrogen and hydrogen gases in a 15.0-L container fitted with a piston in a room with a pressure of $1.00 \mathrm{~atm}$. The piston apparatus allows the container volume to change in order to keep the pressure constant at $1.00 \mathrm{~atm}$. Assume ideal behavior, constant temperature, and complete reaction.
a. What is the partial pressure of ammonia in the container when the reaction is complete?
b. What is the mole fraction of ammonia in the container when the reaction is complete?
c. What is the volume of the container when the reaction is complete?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:33

Problem 71

A cylinder fitted with a movable piston initially contains $2.00 \mathrm{~mol}$ $\mathrm{O}_{2}(\mathrm{~g})$ and an unknown amount of $\mathrm{SO}_{2}(\mathrm{~g})$. The oxygen is known to be in excess. The density of the mixture is $0.8000 \mathrm{~g} / \mathrm{L}$ at some $T$ and $P$. After the reaction has gone to completion, forming $\mathrm{SO}_{3}(g)$, the density of the resulting gaseous mixture is $0.8471 \mathrm{~g} / \mathrm{L}$ at the same $T$ and $P$. Calculate the mass of $\mathrm{SO}_{3}$ formed in the reaction.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
05:19

Problem 72

One way to determine $K_{\mathrm{sp}}$ for the salt $\mathrm{Ca}\left(\mathrm{IO}_{3}\right)_{2}$ is to titrate it with sodium thiosulfate $\left(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\right) .$ First, make a saturated solution of calcium iodate. Then, add KI and a strong acid (hydrochloric acid and sulfuric acid are generally used). The iodate ion will react according to the equation
$$\mathrm{IO}_{3}^{-}+5 \mathrm{I}^{-}+6 \mathrm{H}^{+} \longrightarrow 3 \mathrm{I}_{2}+3 \mathrm{H}_{2} \mathrm{O}$$
Note that molecular iodine is a product of this reaction. Adding a starch indicator will turn the solution of $\mathrm{I}_{2}$ a dark blue-black color. A solution of sodium thiosulfate is added through a buret, which reacts with iodine as follows:
$$\mathrm{I}_{2}+2 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-} \longrightarrow 2 \mathrm{I}^{-}+\mathrm{S}_{4} \mathrm{O}_{6}^{2-}$$
The dark blue-black color disappears, when all of the $\mathrm{I}_{2}$ has reacted. This is the endpoint of the titration.
Consider starting with a $10.0-\mathrm{mL}$ sample of a saturated calcium iodate solution. Upon titrating, you find that $14.9 \mathrm{~mL}$ of $0.100 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ is required to reach the end point of the titration. Calculate $K_{\mathrm{sp}}$ for $\mathrm{Ca}\left(\mathrm{IO}_{3}\right)_{2}$.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
07:13

Problem 73

Although nitrogen trifluoride $\left(\mathrm{NF}_{3}\right)$ is a thermally stable compound, nitrogen triiodide $\left(\mathrm{NI}_{3}\right)$ is known to be a highly explosive material. $\mathrm{NI}_{3}$ can be synthesized according to the equation
$$
\mathrm{BN}(s)+3 \mathrm{IF}(g) \longrightarrow \mathrm{BF}_{3}(g)+\mathrm{NI}_{3}(g)
$$
a. What is the enthalpy of formation for $\mathrm{NI}_{3}(s)$ given the enthalpy of reaction $(-307 \mathrm{~kJ})$ and the enthalpies of formation for $\mathrm{BN}(s)(-254 \mathrm{~kJ} / \mathrm{mol}), \mathrm{IF}(g)(-96 \mathrm{~kJ} / \mathrm{mol})$, and $\mathrm{BF}_{3}(g)(-1136$
$\mathrm{kJ} / \mathrm{mol}$ ?
b. It is reported that when the synthesis of $\mathrm{NI}_{3}$ is conducted using 4 mol IF for every 1 mol BN, one of the by-products isolated is $\left[\mathrm{IF}_{2}\right]^{+}\left[\mathrm{BF}_{4}\right]^{-} .$ What are the molecular geometries of the species in this by-product? What are the hybridizations of the central atoms in each species in the by-product?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
08:51

Problem 74

While selenic acid has the formula $\mathrm{H}_{2} \mathrm{SeO}_{4}$ and thus is directly related to sulfuric acid, telluric acid is best visualized as $\mathrm{H}_{6} \mathrm{TeO}_{6}$ or $\mathrm{Te}(\mathrm{OH})_{6}$
a. What is the oxidation state of tellurium in $\mathrm{Te}(\mathrm{OH})_{6}$ ?
b. Despite its structural differences with sulfuric and selenic acid, telluric acid is a diprotic acid with $\mathrm{p} K_{\mathrm{a} 1}=7.68$ and $\mathrm{p} K_{\mathrm{a} 2}=$ 11.29. Telluric acid can be prepared by hydrolysis of tellurium hexafluoride according to the equation
$$\mathrm{TeF}_{6}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Te}(\mathrm{OH})_{6}(a q)+6 \mathrm{HF}(a q)$$
Tellurium hexafluoride can be prepared by the reaction of elemental tellurium with fluorine gas:
$$\mathrm{Te}(s)+3 \mathrm{~F}_{2}(g) \longrightarrow \mathrm{TeF}_{6}(g)$$
If a cubic block of tellurium (density $=6.240 \mathrm{~g} / \mathrm{cm}^{3}$ ) measuring $0.545 \mathrm{~cm}$ on edge is allowed to react with $2.34 \mathrm{~L}$ of fluorine gas at $1.06 \mathrm{~atm}$ and $25^{\circ} \mathrm{C}$, what is the $\mathrm{pH}$ of a solution of $\mathrm{Te}(\mathrm{OH})_{6}$ formed by dissolving the isolated $\mathrm{TeF}_{6}(g)$ in $115 \mathrm{~mL}$ of water?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
07:03

Problem 75

Captain Kirk has set a trap for the Klingons who are threatening an innocent planet. He has sent small groups of fighter rockets to sites that are invisible to Klingon radar and put a decoy in the open. He calls this the "fishhook" strategy. Mr. Spock has sent a coded message to the chemists on the fighters to tell the ships what to do next. The outline of the message is
Fill in the blanks of the message using the following clues.
(1) Symbol of the halogen whose hydride has the second highest boiling point in the series of HX compounds that are hydrogen halides.
(2) Symbol of the halogen that is the only hydrogen halide, HX, that is a weak acid in aqueous solution.
(3) Symbol of the element whose existence on the sun was known before its existence on earth was discovered.
(4) Symbol of the element whose presence can interfere with the qualitative analysis for $\mathrm{Pb}^{2+}, \mathrm{Hg}_{2}^{2+}$, and $\mathrm{Ag}^{+}$. When chloride ions are added to an aqueous solution of this metal ion, a white precipitate forms with formula MOCl.
(5) Symbol of the Group 6 A element that, like selenium, is a semiconductor.
(6) Symbol for the element known in rhombic and monoclinic forms.
(7) Symbol for the element that exists as diatomic molecules in a yellow-green gas when not combined with another element; its silver, lead, and mercury(T) salts are white and insoluble in water.
(8) Symbol for the most abundant element in and near the earth's crust.
(9) Symbol for the element that seems to give some protection against cancer when a diet rich in this element is consumed.
(10) Symbol for the only noble gas besides xenon that has been shown to form compounds under some circumstances (write the symbol backward and split the letters as shown).
(11) Symbol for the toxic element that, like phosphorus and antimony, forms tetrameric molecules when uncombined with other elements (split the letters of the symbol as shown).
(12) Symbol for the element that occurs as an inert component of air but is a very prominent part of fertilizers and explosives.

Susan Hallstrom
Susan Hallstrom
Numerade Educator