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14 The Halogens: Oxoacids and Oxoacid Salts

14 The Halogens: Oxoacids and Oxoacid Salts

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792



Chapter 19 THE MAIN-GROUP ELEMENTS



Sodium perchlorate (NaClO4) is produced commercially by the electrolytic oxidation of aqueous sodium chlorate and is converted to perchloric acid by reaction

with concentrated HCl:

Electrolysis "

ClO3 -(aq) + H 2O(l)

ClO4 -(aq) + H 2(g)

NaClO4(s) + HCl(aq) ¡ HClO 4(aq) + NaCl(s)



The HClO4 is then concentrated by distillation at reduced pressure.

Pure, anhydrous perchloric acid is a colorless, shock-sensitive liquid that

explodes on heating. It is a powerful and dangerous oxidizing agent, violently oxidizing organic matter and rapidly oxidizing even silver and gold. Perchlorate salts

are also strong oxidants, and they too must be handled with caution. Ammonium

perchlorate (NH4ClO4), in fact, is the oxidizer in the solid booster rockets used to

propel the space shuttle.

Perchlorate ion has been detected in drinking water in 35 states at levels of at

least 4 ppb. It is also present in dairy milk and human breast milk. It’s not yet clear

how much of the ClO 4 - comes from rocket fuel and how much derives from natural

sources. Nevertheless, relatively high levels of ClO 4 - in the environment are of concern because this ion inhibits the uptake of iodide ion by the thyroid gland, which in

turn may lower the level of thyroid hormone in the body and result in neurological

damage.

Iodine differs from the other halogens because it forms more than one perhalic

acid. Paraperiodic acid (H5IO6) is obtained as white crystals (mp 128 °C) when

periodic acid solutions are evaporated. When heated to 100 °C at reduced pressure,

these crystals lose water and are converted to metaperiodic acid (HIO4):

H 5IO6(s)



100 °C

12 mm Hg



" HIO (s) + 2 H O(g)

4

2



Metaperiodic acid is a strong monoprotic acid, whereas paraperiodic acid is a weak

polyprotic acid (Ka1 = 5.1 * 10-4, Ka2 = 4.9 * 10-9). It has an octahedral structure

in which a central iodine atom is bonded to one O atom and five OH groups:



O

HO



OH



O



OH



I

O

O



I

HO

OH



Paraperiodic acid, H5IO6



OH



Metaperiodic acid, HIO4



Chlorine and bromine do not form perhalic acids of the type H5XO6 because their

smaller sizes favor a tetrahedral structure over an octahedral one.



INQUIRY HOW DO LASER PRINTERS WORK?



793



INQUIRY HOW DO LASER PRINTERS WORK?

Laser printers are the descendants of the plain-paper photocopy machine; the prototype laser printer was built from one. A half century ago, the photocopier

revolutionized the way offices handle paper by making possible the creation of

numerous, identical copies of a document. Today, the laser printers that sit on our

desktops make possible the rapid and economical production of original, computer–

generated documents.

Photocopiers and laser printers take advantage of an unusual property of selenium, the group 6A element below sulfur in the periodic table. Selenium is a

photoconductor, a substance that is a poor electrical conductor when dark but whose

conductivity increases (by a factor of 1000) when exposed to light. When the light is

removed, the conductivity again drops.

As illustrated in Figure 19.13, the image-forming process in a laser printer begins

when a selenium-coated drum, kept in the dark, is given a large, uniform negative

charge. As the drum rotates, it is exposed to computer-generated flashes of infrared

laser light (l = 780 nm) directed by lenses and mirrors. Areas on the drum hit by the

precisely focused laser light become conducting and lose most of their negative

charge. These charge-depleted areas correspond to the dark parts of the document.

Those areas that correspond to the light parts of the document remain nonconducting and retain their large negative charge. Thus, an image of the document is formed

on the drum as an array of slightly negative (largely neutralized) areas amidst the

large area of undepleted negative charges.

Figure 19.13

Mirror

2



Laser



Selenium-coated

drum

Expose drum

to laser



1

Charge

drum



5

Document

out



3



Develop

image



Clean

drum



Plain

paper in

Transfer toner

to paper



Heat to

fix toner



4



Following its formation, the image is developed by exposing the drum to negatively charged dry ink particles (toner), which are repelled from the strongly negative

areas of the drum and collect in the largely neutralized areas. The developed image is

then transferred to paper by passing a sheet of paper between the drum and a positively charged development electrode, which induces the negatively charged toner

particles to jump from the drum to the paper.

At this point, the toner could easily be brushed off the paper; you may have done

this if you’ve ever opened a copier or printer to remove a paper jam. The toner particles, made of a low-melting plastic resin mixed with carbon black, are affixed to the

paper by the fuser, a hot roller at about 170 °C that melts and bonds the toner to the

paper. The document then rolls out of the machine, and the drum is restored to its

original condition by flooding it with light to remove all remaining charges and gently scraping off any bits of excess toner.



The laser printer process.

1 A selenium-coated rotating drum is

given a large, uniform negative

charge.

2 The drum is then exposed to a

scanning laser beam, which depletes

the charge in the exposed areas.

3 Negatively charged toner particles

applied to the drum avoid the areas

with large negative charges and

adhere to the charge-depleted areas.

4 The image is transferred from the

drum to a sheet of paper. Heating

then fixes the image.

5 The drum is flooded with light and

cleaned to ready it for printing the

next page.



794



Chapter 19 THE MAIN-GROUP ELEMENTS



The laser printing process has been adapted for printing color documents. To

obtain a color image, four toner colors are needed to generate the entire spectrum of

colors: cyan (blue-green), magenta (red-purple), yellow, and black. Color printers

work like monochrome printers, except they repeat the printing process four times,

once for each color. Careful alignment of the colors with one another is required to

obtain a crisp image.

Ī PROBLEM 19.12 What would be the effect of coating the laser printer drum with

copper instead of selenium? Explain.



CONCEPTUAL PROBLEMS



795



SUMMARY

The main-group elements are the s-block elements of groups 1A

and 2A and the p-block elements of groups 3A–8A. From left to

right across the periodic table, ionization energy, electronegativity,

and nonmetallic character generally increase, while atomic radius

and metallic character decrease. From top to bottom of a group in

the periodic table, ionization energy, electronegativity, and nonmetallic character generally decrease, while atomic radius and

metallic character increase. The second-row elements form strong

multiple bonds but are generally unable to form more than four

bonds because of the small size of their atoms.

The group 3A elements—B, Al, Ga, In, and Tl—are metals

except for boron, which is a semimetal. Boron is a semiconductor

and forms molecular compounds. Boranes, such as diborane

(B2H6), are electron-deficient molecules that contain three-center,

two-electron bonds (B ¬ H ¬ B).

The group 4A elements—C, Si, Ge, Sn, and Pb—exhibit the

usual increase in metallic character down the group. They often

adopt an oxidation state of +4, but the +2 state becomes increasingly more stable from Ge to Sn to Pb. In elemental form, carbon

exists as diamond, graphite, graphene, and fullerene.

Silicon, the second most abundant element in the Earth’s crust,

is obtained by reducing silica sand (SiO2) with coke. It is purified

for use in the semiconductor industry by zone refining. In the

silicates, SiO4 tetrahedra share common O atoms to give silicon

oxoanions with ring, chain, layer, and extended three-dimensional



structures. In aluminosilicates, such as KAlSi3O8, Al3+ replaces some

of the Si 4+ .

Molecular nitrogen (N2) is unreactive because of its strong

N ‚ N triple bond. Nitrogen exhibits all oxidation states between

-3 and + 5. Nitric acid is manufactured by the Ostwald process.

Phosphorus, the most abundant group 5A element, exists in

two common allotropic forms—white phosphorus, which contains

highly reactive tetrahedral P4 molecules, and red phosphorus, which is polymeric. The most common oxidation states of P

are - 3, as in phosphine (PH3); + 3, as in PCl3, P4O6, and H3PO3;

and +5, as in PCl5, P4O10, and H3PO4.

Sulfur is obtained from underground deposits and is recovered from natural gas and crude oil. The properties of sulfur

change dramatically on heating as the S8 rings of rhombic sulfur

open and polymerize to give long chains, which then fragment at

higher temperatures. The most common oxidation states of S are

- 2, as in H2S; +4, as in SO2 and H2SO3; and + 6, as in SO3 and

H2SO4. Sulfuric acid, the world’s most important industrial chemical, is manufactured by the contact process.

Chlorine, bromine, and iodine form a series of oxoacids: hypohalous acid (HXO), halous acid (HXO2 for X = Cl), halic acid

(HXO3), and perhalic acid (HXO4). Acid strength increases as the

oxidation state of the halogen increases from +1 to + 7. Iodine

forms two perhalic acids, HIO4 and H5IO6. Halogen oxoacids and

their salts are strong oxidizing agents.



KEY WORDS

aluminosilicate

boranes 768

carbide 773



776



contact process 789

Ostwald process 782

silicate 774



three-center, two-electron

bond 768



zone refining



774



CONCEPTUAL PROBLEMS

Problems 19.1–19.12 appear within the chapter.

19.13 Locate each of the following

periodic table:

(a) Main-group elements

(c) p-Block elements

(e) Nonmetals



(f) Group 5A element that forms the strongest p bonds



groups of elements on the

(b) s-Block elements

(d) Main-group metals

(f) Semimetals



19.15 Locate the following elements on the periodic table:

(a) Elements that are gases at room temperature (25 °C)

(b) A main-group element that is a liquid at 25 °C

(c) Nonmetals that are solids at 25 °C

(d) Elements that exist as diatomic molecules at 25 °C

19.14 Locate each of the following elements on the periodic table:

(a) Element with the lowest ionization energy

(b) Most electronegative element

(c) Group 4A element with the largest atomic radius

(d) Group 6A element with the smallest atomic radius

(e) Group 3A element that is a semiconductor



796



Chapter 19 THE MAIN-GROUP ELEMENTS



19.16 Locate the following elements on the periodic table, and

write the formula of a compound that justifies each of your

answers:

(a) Two nonmetals that can form more than four bonds

(b) Two nonmetals that form a maximum of four bonds

(c) Two nonmetals that form oxides that are gases at 25 °C

(d) A nonmetal that forms an oxide that is a solid at 25 °C



(a) Identify the nonfluorine atom in each case, and write

the molecular formula of each fluoride.

(b) Explain why the fluorides of nitrogen and phosphorus

have different molecular structures, but the fluorides of

carbon and silicon have the same molecular structure.

19.19 The following models represent the structures of binary

oxides of second- and third-row elements in their highest

oxidation states:



19.17 Consider the six second- and third-row elements in groups

5A–7A of the periodic table:

N O F

P S Cl



Possible molecular structures for common allotropes of

these elements are shown below:



(a) What is the molecular structure of each of the six

elements?

(b) Using electron-dot structures, explain why each element

has its particular molecular structure.

(c) Explain why nitrogen and phosphorus have different

molecular structures and why oxygen and sulfur have

different molecular structures, but fluorine and chlorine have the same molecular structure.

19.18 Consider the six second- and third-row elements in groups

4A–6A of the periodic table:

C N O

Si P S



(a) Identify the non-oxygen atom in each case, and write

the molecular formula for each oxide.

(b) Draw an electron-dot structure for each oxide. For

which oxides are resonance structures needed?

19.20 The following models represent the structures of binary

hydrides of second-row elements:



(a) Identify the nonhydrogen atom in each case, and write

the molecular formula for each hydride.

(b) Draw an electron-dot structure for each hydride. For

which hydride is there a problem in drawing the structure? Explain.

19.21 The following pictures represent various silicate anions.

Write the formula and charge of each anion.

(a)



Possible structures for the binary fluorides of each of these

elements in its highest oxidation state are shown below.



(b)



(c)



SECTION PROBLEMS



797



SECTION PROBLEMS

General Properties and Periodic Trends (Sections 19.1–19.2)

19.22 Which element in each of the following pairs has the higher

ionization energy?

(a) S or Cl

(b) Si or Ge (c) In or O

19.23 Arrange the following elements in order of increasing ionization energy:

(a) P

(b) K

(c) Al

(d) F

19.24 Which element in each of the following pairs has the larger

atomic radius?

(a) B or Al (b) P or S

(c) Pb or Br

19.25 Arrange the following elements in order of increasing

atomic radius:

(a) As

(b) O

(c) Sn

(d) S

19.26 Which element in each of the following pairs has the higher

electronegativity?

(a) Te or I

(b) N or P

(c) In or F

19.27 Arrange the following elements in order of increasing

electronegativity:

(a) N

(b) Ge

(c) O

(d) P

19.28 Which element in each of the following pairs has more

metallic character?

(a) Si or Sn (b) Ge or Se (c) Bi or I

19.29 Which element in each of the following pairs has more nonmetallic character?

(a) S or Te

(b) Cl or P

(c) Bi or Br

19.30 Which compound in each of the following pairs is more

ionic?

(a) CaH2 or NH3

(b) P4O6 or Ga2O3

(c) SiCl4 or KCl

(d) BCl3 or AlCl3

19.31 Which compound in each of the following pairs is more

covalent?

(a) PCl3 or AlF3

(b) CaO or NO

(c) NH3 or KH

(d) SnO2 or SiO2

19.32 Which of the following compounds are molecular, and

which have an extended three-dimensional structure?

(a) B2H6

(b) KAlSi3O8 (c) SO3

(d) GeCl4

19.33 Which of the following compounds are molecular, and

which have an extended three-dimensional structure?

(a) KF

(b) P4O10

(c) SiCl4

(d) CaMgSi2O6

19.34 Which oxide in each of the following pairs is more acidic?

(a) Al2O3 or P4O10

(b) B2O3 or Ga2O3

(c) SO2 or SnO2

(d) As2O3 or N2O3

19.35 Which oxide in each of the following pairs is more basic?

(a) SO2 or SnO2

(b) In2O3 or Ga2O3

(c) Al2O3 or N2O5

(d) BaO or MgO

19.36 Consider the elements C, Se, B, Sn, Cl. Identify the element

on this list that:

(a) Has the largest atomic radius

(b) Is the most electronegative

(c) Is the best electrical conductor

(d) Has a maximum oxidation state of +6

(e) Forms a hydride with the empirical formula XH3



19.37 Consider the elements N, Si, Al, S, F. Identify which of

these elements:

(a) Has the highest ionization energy

(b) Has the most metallic character

(c) Forms the strongest p bonds

(d) Is a semiconductor

(e) Forms a 2– anion

19.38 BF3 reacts with F - to give BF4 - , but AlF3 reacts with F - to

give AlF6 3- . Explain.

19.39 GeCl4 reacts with Cl - to give GeCl6 2- , but CCl4 does not

react with excess Cl - . Explain.

19.40 At ordinary temperatures, sulfur exists as S8 but oxygen

exists as O2. Explain.

19.41 Elemental nitrogen exists as N2, but white phosphorus

exists as P4. Explain.

The Group 3A Elements (Sections 19.3–19.5)

19.42 What is the most common oxidation state for each of the

group 3A elements?

19.43 What is the oxidation state of the group 3A element in each

of the following compounds?

(a) NaBF4

(b) GaCl3

(c) TlCl

(d) B2H6

19.44 List three ways in which the properties of boron differ from

those of the other group 3A elements.

19.45 Explain why the properties of boron differ so markedly

from the properties of the other group 3A elements.

19.46 How is crystalline boron prepared? Write a balanced equation for the reaction.

19.47 Write a balanced equation for the reduction of boron oxide

by magnesium.

19.48 Tell what is meant by:

(a) An electron-deficient molecule

(b) A three-center, two-electron bond

Illustrate each definition with an example.

19.49 Describe the structure of diborane (B2H6), and explain why

the bridging B ¬ H bonds are longer than the terminal

B ¬ H bonds.

19.50 Identify the group 3A element that best fits each of the following descriptions:

(a) Is the most abundant element of the group

(b) Is stable in the +1 oxidation state

(c) Is a semiconductor

(d) Forms a molecular fluoride

19.51 Identify the group 3A element that best fits each of the following descriptions:

(a) Has an unusually low melting point

(b) Is the most electronegative

(c) Is extremely toxic

(d) Forms an acidic oxide



798



Chapter 19 THE MAIN-GROUP ELEMENTS



The Group 4A Elements (Sections 19.6–19.8)

19.52 Identify the group 4A element that best fits each of the following descriptions:

(a) Prefers the +2 oxidation state

(b) Forms the strongest p bonds

(c) Is the second most abundant element in the Earth’s

crust

(d) Forms the most acidic oxide

19.53 Select the group 4A element that best fits each of the following descriptions:

(a) Forms the most basic oxide

(b) Is the least dense semimetal

(c) Is the second most abundant element in the human

body

(d) Is the most electronegative

19.54 Describe the geometry of each of the following molecules

or ions, and tell which hybrid orbitals are used by the central atom:

(a) GeBr4

(b) CO2

(c) CO3 2(d) SnCl3 19.55 What is the geometry of each of the following molecules or

ions, and which hybrid orbitals are used by the central

atom?

(a) SiO4 4(b) CCl4

(c) SnCl2

(d) HCN

19.56 List three properties of diamond, and account for them in

terms of structure and bonding.

19.57 Describe the structure and bonding in graphite, and

explain why graphite is a good lubricant and a good electrical conductor.

19.58 What is graphene, and how does it differ from graphite?

19.59 Fullerene is soluble in nonpolar solvents, but graphite isn’t.

Explain.

19.60 Give the name and formula of a compound in which carbon exhibits an oxidation state of:

(a) +4

(b) +2

(c) -4

19.61 Give an example of an ionic carbide. What is the oxidation

state of carbon in this substance?

19.62 List three commercial uses for carbon dioxide, and relate

each use to one of carbon dioxide’s properties.

19.63 Why are CO and CN - so toxic to humans?

19.64 Describe the preparation of silicon from silica sand, and tell

how silicon is purified for use in semiconductor devices.

Write balanced equations for all reactions.

19.65 How do the structures and properties of elemental silicon

and germanium differ from those of tin and lead?

19.66 Using the shorthand notation of Figure 19.5 (page 775),

draw the structure of the silicate anion in:

(a) K4SiO4

(b) Ag10Si4O13

What is the relationship between the charge on the anion

and the number of terminal O atoms?

19.67 Using the shorthand notation of Figure 19.5 (page 775),

draw the structure of the cyclic silicate anion in which four

SiO4 tetrahedra share O atoms to form an eight-membered

ring of alternating Si and O atoms. Give the formula and

charge of the anion.



19.68 The silicate anion in the mineral kinoite is a chain of three

SiO4 tetrahedra that share corners with adjacent tetrahedra.

The mineral also contains Ca2+ ions, Cu2+ ions, and water

molecules in a 1 : 1 : 1 ratio.

(a) Give the formula and charge of the silicate anion.

(b) Give the complete formula for the mineral.

19.69 Suggest a plausible structure for the silicate anion in each

of the following minerals:

(a) Spodumene, LiAlSi2O6 (b) Wollastonite, Ca3Si3O9

(c) Thortveitite, Sc2Si2O7

(d) Albite, NaAlSi3O8

The Group 5A Elements (Sections 19.9–19.11)

19.70 Identify the group 5A element(s) that best fits each of the

following descriptions:

(a) Makes up part of bones and teeth

(b) Forms stable salts containing M 3+ ions

(c) Is the most abundant element in the atmosphere

(d) Forms a basic oxide

19.71 Identify the group 5A element that best fits each of the following descriptions:

(a) Forms strong p bonds (b) Is a metal

(c) Is the most abundant group 5A element in the Earth’s crust

(d) Forms oxides with the group 5A element in the +1, +2,

and +4 oxidation states

19.72 Give the chemical formula for each of the following compounds, and indicate the oxidation state of the group 5A

element:

(a) Nitrous oxide

(b) Hydrazine

(c) Calcium phosphide

(d) Phosphorous acid

(e) Arsenic acid

19.73 Give the chemical formula for each of the following compounds, and indicate the oxidation state of the group 5A

element:

(a) Nitric oxide

(b) Nitrous acid

(c) Phosphine

(d) Tetraphosphorus decoxide

(e) Phosphoric acid

19.74 Draw an electron-dot structure for N2, and explain why

this molecule is so unreactive.

19.75 Draw electron-dot structures for:

(a) Nitrous oxide (b) Nitric oxide (c) Nitrogen dioxide

Predict the molecular geometry of each, and indicate which

are expected to be paramagnetic.

19.76 Predict the geometry of each of the following molecules or

ions:

(a) NO2 (b) PH3

(c) PF5

(d) PCl4 +

19.77 Predict the geometry of each of the following molecules or

ions:

(a) PCl6 (b) N2O

(c) H3PO3

(d) NO3 19.78 Describe the structures of the white and red allotropes

of phosphorus, and explain why white phosphorus is so

reactive.

19.79 Draw the structure of each of the following molecules:

(a) Tetraphosphorus hexoxide

(b) Tetraphosphorus decoxide

(c) Phosphorous acid

(d) Phosphoric acid



SECTION PROBLEMS



19.80 Account for each of the following observations:

(a) Phosphorous acid is a diprotic acid.

(b) Nitrogen doesn’t exist as a four-atom molecule like P4.

19.81 Account for each of the following observations:

(a) Nitric acid is a strong oxidizing agent, but phosphoric

acid is not.

(b) Phosphorus, arsenic, and antimony form trichlorides

and pentachlorides, but nitrogen forms only NCl3.

19.82 Write a balanced equation to account for each of the following observations:

(a) Nitric oxide turns brown when exposed to air.

(b) Nitric acid turns yellow-brown on standing.

(c) Silver dissolves in dilute HNO3, yielding a colorless gas.

(d) Hydrazine reduces iodine to I - and in the process is

oxidized to N2 gas.

19.83 Describe the process used for the industrial production of

the following chemicals:

(a) Nitrogen

(b) Ammonia

(c) Nitric acid

(d) Phosphoric acid

Write balanced equations for all chemical reactions.

The Group 6A Elements (Sections 19.12–19.13)

19.84 Identify the group 6A element that best fits each of the following descriptions:

(a) Is the most electronegative

(b) Is a semimetal

(c) Is radioactive

(d) Is the most abundant element in the Earth’s crust

19.85 Identify the group 6A element that best fits each of the following descriptions:

(a) Is a metal

(b) Is the most abundant element in the human body

(c) Is the strongest oxidizing agent

(d) Has the most negative electron affinity

19.86 Describe the structure of the sulfur molecules in:

(a) Rhombic sulfur

(b) Monoclinic sulfur

(c) Plastic sulfur

(d) Liquid sulfur above 160 °C

19.87 The viscosity of liquid sulfur increases sharply at about

160 °C and then decreases again above 200 °C. Explain.

19.88 Give the name and formula of two compounds in which

sulfur exhibits an oxidation state of:

(a) -2

(b) +4

(c) + 6

19.89 What is the oxidation state of sulfur in each of the following compounds?

(c) H2SO3

(a) HgS

(b) Ca(HSO4)2

(d) FeS2

(e) SF4

19.90 Describe the contact process for the manufacture of sulfuric

acid, and write balanced equations for all reactions.

19.91 Describe a convenient laboratory method for preparing

each of the following compounds, and write balanced

equations for all reactions:

(a) Sulfur dioxide

(b) Hydrogen sulfide

(c) Sodium hydrogen sulfate



799



19.92 Write a balanced net ionic equation for each of the following reactions:

(a) Zn(s) + dilute H 2SO4(aq) ¡

(b) BaSO3(s) + HCl(aq) ¡

(c) Cu(s) + hot, conc H 2SO4(l) ¡

(d) H 2S(aq) + I 2(aq) ¡

19.93 Write a balanced net ionic equation for each of the following reactions:

(a) ZnS(s) + HCl(aq) ¡

(b) H 2S(aq) + Fe(NO3)3(aq) ¡

(c) Fe(s) + dilute H 2SO4(aq) ¡

(d) BaO(s) + H 2SO4(aq) ¡

19.94 Account for each of the following observations:

(a) H2SO4 is a stronger acid than H2SO3.

(b) SF4 exists, but OF4 does not.

(c) The S8 ring is nonplanar.

19.95 Account for each of the following observations:

(a) Oxygen is more electronegative than sulfur.

(b) Sulfur forms long S n chains, but oxygen does not.

(c) The SO3 molecule is trigonal planar, but the SO3 2- ion

is trigonal pyramidal.

Halogen Oxoacids and Oxoacid Salts (Section 19.14)

19.96 Write the formula for each of the following compounds,

and indicate the oxidation state of the halogen:

(a) Bromic acid

(b) Hypoiodous acid

(c) Sodium chlorite

(d) Potassium metaperiodate

19.97 Write the formula for each of the following compounds,

and indicate the oxidation state of the halogen:

(a) Potassium hypobromite

(b) Paraperiodic acid

(c) Sodium bromate

(d) Chlorous acid

19.98 Name each of the following compounds:

(a) HIO3

(b) HClO2

(c) NaOBr

(d) LiClO4

19.99 Name each of the following compounds:

(a) KClO2

(b) HIO4

(c) HOBr

(d) NaBrO3

19.100 Write an electron-dot structure for each of the following

molecules or ions, and predict the molecular geometry:

(a) HIO3

(b) ClO2 (c) HOCl

(d) IO6 519.101 Write an electron-dot structure for each of the following

molecules or ions, and predict the molecular geometry:

(a) BrO4 (b) ClO3 (c) HIO4

(d) HOBr

19.102 Explain why acid strength increases in the order

HClO 6 HClO2 6 HClO 3 6 HClO 4.

19.103 Explain why acid strength increases in the order

HIO 6 HBrO 6 HClO.

19.104 Write a balanced net ionic equation for each of the following reactions:

(a) Br2(l) + cold NaOH(aq) ¡

(b) Cl2(g) + cold H 2O(l) ¡

(c) Cl2(g) + hot NaOH(aq) ¡

19.105 Write a balanced equation for the reaction of potassium

chlorate and sucrose. The products are KCl(s), CO2(g), and

H 2O(g).



800



Chapter 19 THE MAIN-GROUP ELEMENTS



CHAPTER PROBLEMS

19.106 Write a balanced net ionic equation for the reaction

between magnesium and hot, concentrated sulfuric acid, a

reaction similar to that between hot, concentrated sulfuric

acid and copper.

19.107 Choose the compound in Table 19.6 that is used as a rocket

fuel. What nitrogen-containing compound is used as the

oxidizer?

19.108 Does the silicate hedenbergite, CaFeSi2O6, contain singlestranded or double-stranded silicate chains? (Draw

comparisons with Figures 19.6 and 19.7.)

19.109 An iron object exposed to rain is eventually damaged by

rusting, but a similarly placed aluminum object is visibly

unchanged. Explain.

19.110 Hydrazine can be used to remove small amounts of dissolved

oxygen from the water used in boilers. Write a balanced equation for the reaction if the products are nitrogen and water.

19.111 Iodine forms the acid anhydride I2O5. Write a balanced

equation for the reaction of this anhydride with water, and

name the acid that is formed.

19.112 Which compound in each of the following pairs has the

higher melting point?

(a) LiCl or PCl3

(b) CO2 or SiO2

(c) P4O10 or NO2

19.113 Which element in each of the following pairs is the better

electrical conductor?

(a) B or Ga

(b) In or S

(c) Pb or P

19.114 Draw the structure of graphene.

19.115 Compare and contrast the properties of ammonia and

phosphine.

19.116 How many of the four most abundant elements in the

Earth’s crust and in the human body can you identify without consulting Figure 19.1?

19.117 Identify as many of the 10 most important industrial chemicals as you can without consulting Table 19.1.

19.118 Which of the group 4A elements have allotropes with the

diamond structure? Which have metallic allotropes? How

does the variation in the structure of the group 4A elements

illustrate how metallic character varies down a periodic

group?

19.119 Write a balanced chemical equation for a laboratory preparation of each of the following compounds:

(a) NH3

(b) CO2

(c) B2H6 (diborane)

(d) C2H2 (acetylene) (e) N2O

(f) NO2

19.120 Write balanced equations for the reactions of (a) H3PO4 and

(b) B(OH)3 with water. Classify each acid as a Brønsted–

Lowry acid or a Lewis acid.

19.121 What oxoanion is used for these purposes?

(a) Oxidizing agent in space shuttle booster rockets

(b) Oxidizing agent in chlorine bleach

(c) Oxidizing agent in matches and fireworks



19.122 Account for each of the following observations:

(a) Diamond is extremely hard and high melting, whereas

graphite is very soft and high melting.

(b) Chlorine does not form a perhalic acid, H5ClO6.

19.123 So-called fuming sulfuric acid is formed when sulfur trioxide dissolves in anhydrous sulfuric acid to form H2S2O7.

Propose a structure for H2S2O7, which contains an

S ¬ O ¬ S linkage.

19.124 Chlorine reacts with molten sulfur to yield disulfur dichloride,

a yellowish-red liquid. Propose a structure for disulfur

dichloride.

19.125 The organ pipes in an unheated Estonian church are pitted

and crumbling to powder in places. Suggest an explanation, given that the pipes are made from tin.

19.126 Of ammonia, hydrazine, and hydroxylamine, which reacts

to the greatest extent with the weak acid HNO2? Consult

Appendix C for equilibrium constants.

19.127 A fullerene that is 97.28% C has an atom within the C60

cage. Is the compound He@C60 or Ne@C60?

19.128 Suggest a structure for the mixed aluminum–boron

hydride AlBH6.

19.129 Suggest a benefit and a limitation to using gallium as the

material in a thermometer.

19.130 A sample of P4 burned in excess oxygen and formed a

phosphorus oxide. The phosphorus oxide was dissolved

carefully in enough water to make 1.00 L of solution with

pH = 1.93. What is the identity of the phosphorus oxide

and the oxoacid that was formed, and how much P4, in

grams, was burned? See Appendix C for acid dissociation

constants.

19.131 Give one example from main-group chemistry that illustrates each of the following descriptions:

(a) Covalent network solid

(b) Disproportionation reaction

(c) Paramagnetic oxide

(d) Polar molecule that violates the octet rule

(e) Lewis acid

(f) Amphoteric oxide

(g) Semiconductor

(h) Strong oxidizing agent

(i) Allotropes

19.132 Could the strain in the P4 molecule be reduced by using sp 3

hybrid orbitals in bonding instead of pure p orbitals?

Explain.

19.133 Carbon is an essential element in the molecules on

which life is based. Would silicon be equally satisfactory?

Explain.



MULTICONCEPT PROBLEMS



801



MULTICONCEPT PROBLEMS

19.134 An important physiological reaction of nitric oxide (NO) is

its interaction with the superoxide ion (O2 -) to form the

peroxynitrite ion (ONOO -).

(a) Write electron-dot structures for NO, O2 - , and

ONOO - , and predict the O ¬ N ¬ O bond angle in

ONOO - .

(b) The bond length in NO (115 pm) is intermediate

between the length of an NO triple bond and an NO

double bond. Account for the bond length and the

paramagnetism of NO using molecular orbital theory.

19.135 Consider phosphorous acid, a polyprotic acid with formula

H3PO3.

(a) Draw two plausible structures for H3PO3. For each one,

predict the shape of the pH titration curve for the titration of the H 3PO3 (Ka1 = 1.0 * 10-2) with aqueous

NaOH.

(b) For the structure with the H atoms in two different

environments, calculate the pH at the first and second

equivalence points assuming that 30.00 mL of

0.1240 M H 3PO3 (Ka2 = 2.6 * 10-7) is titrated with

0.1000 M NaOH.

19.136 We’ve said that the +1 oxidation state is uncommon for

indium but is the most stable state for thallium. Verify this

statement by calculating E° and ¢G° (in kilojoules) for the

disproportionation reaction

3 M + (aq) ¡ M 3 + (aq) + 2 M(s)



M = In or Tl



Is disproportionation a spontaneous reaction for In+

and/or Tl + ? Standard reduction potentials for the relevant

half-reactions are

In3 + (aq) + 2 e - ¡ In+(aq)

+



-



E° = -0.44 V



In (aq) + e ¡ In(s)



E° = -0.14 V



Tl3 + (aq) + 2 e - ¡ Tl + (aq)



E° = +1.25 V



+



-



Tl (aq) + e ¡ Tl(s)



E° = -0.34 V



19.137 Terrorists often use ammonium nitrate fertilizer as an

ingredient in car bombs. When ammonium nitrate

explodes, it decomposes to gaseous nitrogen, oxygen, and

water vapor. The force of the explosion results from the

sudden production of a huge volume of hot gas.

(a) Write a balanced equation for the reaction.

(b) What volume of gas (in liters) is produced from the

explosion of 1.80 m3 of solid NH4NO3? Assume that the

gas has a temperature of 500 °C and a pressure of

1.00 atm. The density of NH4NO3 is 1.725 g/cm3.

(c) Use the thermodynamic data in Appendix B to calculate the amount of heat (in kilojoules) released in the

reaction.



19.138 It has been claimed that NH4NO3 fertilizer can be rendered

unexplodable (see Problem 19.137) by adding compounds

such as diammonium hydrogen phosphate, (NH4)2HPO4.

Analysis of such a desensitized sample of NH4NO3

showed the mass % nitrogen to be 33.81%.

(a) Assuming that the mixture contains only NH4NO3 and

(NH4)2HPO4, what is the mass percent of each of these

two components?

(b) A 0.965 g sample of the mixture was dissolved in

enough water to make 50.0 mL of solution. What is the

pH of the solution? (Hint: The strongest base present is

HPO4 2- .)

19.139 A 5.00 g quantity of white phosphorus was burned in an

excess of oxygen, and the product was dissolved in enough

water to make 250.0 mL of solution.

(a) Write balanced equations for the reactions.

(b) What is the pH of the solution?

(c) When the solution was treated with an excess of aqueous Ca(NO3)2, a white precipitate was obtained. Write a

balanced equation for the reaction, and calculate the

mass of the precipitate in grams.

(d) The precipitate in part (c) was removed, and the solution that remained was treated with an excess of zinc,

yielding a colorless gas that was collected at 20 °C and

742 mm Hg. Identify the gas, and determine its volume.

19.140 A 500.0 mL sample of an equilibrium mixture of gaseous

N2O4 and NO2 at 25 °C and 753 mm Hg pressure was

allowed to react with enough water to make 250.0 mL of

solution at 25 °C. You may assume that all the dissolved

N2O4 is converted to NO2, which disproportionates in

water, yielding a solution of nitrous acid and nitric acid.

Assume further that the disproportionation reaction goes

to completion and that none of the nitrous acid disproportionates. The equilibrium constant Kp for the reaction

N2O4(g) Δ 2 NO2(g) is 0.113 at 25 °C. Ka for HNO2 is

4.5 * 10- 4 at 25 °C.

(a) Write a balanced equation for the disproportionation

reaction.

(b) What is the molar concentration of NO2 - , and what is

the pH of the solution?

(c) What is the osmotic pressure of the solution in

atmospheres?

(d) How many grams of lime (CaO) would be needed to

neutralize the solution?



CHAPTER



20



Transition Elements and

Coordination Chemistry



The color of the Carmen Lucia Ruby is due to transitions of

d electrons in Cr3+ ions.



CONTENTS



802



20.1



Electron Configurations



20.8



Isomers



20.2



Properties of Transition Elements



20.9



Enantiomers and Molecular Handedness



20.3



Oxidation States of Transition Elements



20.10 Color of Transition Metal Complexes



20.4



Chemistry of Selected Transition Elements



20.11 Bonding in Complexes: Valence Bond Theory



20.5



Coordination Compounds



20.12 Crystal Field Theory



20.6



Ligands



INQUIRY



20.7



Naming Coordination Compounds



How Do Living Things Acquire Nitrogen?



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