Chapter 19

Explain why HF is a weak acid, whereas HCl, HBr, and HI are all strong acids.

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 b. xenon trioxide c. xenon difluoride d. xenon tetrafluoride e. xenon hexafluoride

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. \(\mathrm{KrF}_{2}\) c. \(\mathrm{XeO}_{2} \mathrm{F}_{2}\) b. \(\mathrm{KrF}_{4}\) d. \(\mathrm{XeO}_{2} \mathrm{F}_{4}\)

Although He is the second most abundant element in the universe, it is very rare on the earth. Why?

There is evidence that radon reacts with fluorine to form compounds similar to those formed by xenon and fluorine. Predict the formulas of these \(\operatorname{RnF}_{x}\) compounds. Why is the chemistry of radon difficult to study?

The inert-pair effect is sometimes used to explain the tendency of heavier members of Group \(3 \mathrm{A}(13)\) to exhibit +1 and +3 oxidation states. What does the inert-pair effect reference? [Hint: Consider the valence electron configuration for Group \(3 \mathrm{A}(13)\) elements.

How could you determine experimentally whether the compound \(\mathrm{Ga}_{2} \mathrm{Cl}_{4}\) contains two gallium(II) ions or one gallium(I) and one gallium(III) ion? (Hint: Consider the electron configurations of the three possible ions.)

Slaked lime, \(\mathrm{Ca}(\mathrm{OH})_{2},\) is used to soften hard water by removing calcium ions from hard water through the reaction $$\begin{array}{r}\mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{Ca}^{2+}(a q)+2 \mathrm{HCO}_{3}^{-}(a q) \rightarrow \\\2 \mathrm{CaCO}_{3}(s)+2 \mathrm{H}_{2} \mathrm{O}(l)\end{array}$$.Although \(\mathrm{CaCO}_{3}(s)\) is considered insoluble, some of it does dissolve in aqueous solutions. Calculate the molar solubility of \(\mathrm{CaCO}_{3}\) in water \(\left(K_{\mathrm{sp}}=8.7 \times 10^{-9}\right)\).

EDTA is used as a complexing agent in chemical analysis. Solutions of EDTA, usually containing the disodium salt \(\mathrm{Na}_{2} \mathrm{H}_{2} \mathrm{EDTA},\) are also used to treat heavy metal poisoning. The equilibrium constant for the following reaction is \(6.7 \times 10^{21}\) Calculate \(\left[\mathrm{Pb}^{2+}\right]\) at equilibrium in a solution originally \(0.0050 M\) in \(\mathrm{Pb}^{2+}, 0.075 M\) in \(\mathrm{H}_{2} \mathrm{EDTA}^{2-},\) and buffered at \(\mathrm{pH}=7.00\):.

Photogray lenses contain small embedded crystals of solid silver chloride. Silver chloride is light-sensitive because of the reaction $$ \operatorname{AgCl}(s) \stackrel{\text { hv }}{\longrightarrow} \mathrm{Ag}(s)+\mathrm{Cl} $$ 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?

Draw Lewis structures for the \(\mathrm{AsCl}_{4}^{+}\) and \(\mathrm{AsCl}_{6}^{-}\) ions. What type of reaction (acid-base, oxidation- reduction, or the like) is the following?$$2 \mathrm{AsCl}_{5}(g) \longrightarrow \mathrm{AsCl}_{4} \mathrm{AsCl}_{6}(s)$$.

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

What is a disproportionation reaction? Use the following reduction potentials $$\begin{array}{ll} \mathrm{ClO}_{3}^{-}+3 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}_{2}+\mathrm{H}_{2} \mathrm{O} & \mathscr{C}^{\circ}=1.21 \mathrm{V} \\ \mathrm{HClO}_{2}+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}+\mathrm{H}_{2} \mathrm{O} & \mathscr{C}^{\circ}=1.65 \mathrm{V} \end{array}$$ to predict whether \(\mathrm{HClO}_{2}\) will disproportionate.

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.

Hydrogen gas is being considered as a fuel for automobiles. There are many chemical means for producing hydrogen gas from water. One of these reactions is $$\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)$$. In this case the form of carbon used is graphite. a. Calculate \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) for this reaction using data from Appendix 4. b. At what temperature is \(\Delta G^{\circ}=\) zero for this reaction? Assume \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) do not depend on temperature.

Molten \(\mathrm{CaCl}_{2}\) is electrolyzed for \(8.00 \mathrm{h}\) to produce \(\mathrm{Ca}(s)\) and \(\mathrm{Cl}_{2}(g)\) a. What current is needed to produce \(5.52 \mathrm{kg}\) of calcium metal? b. If \(5.52 \mathrm{kg}\) calcium metal is produced, what mass (in \(\mathrm{kg}\) ) of \(\mathrm{Cl}_{2}\) is produced?

Calculate the solubility of \(\mathrm{Mg}(\mathrm{OH})_{2}\left(K_{\mathrm{sp}}=8.9 \times 10^{-12}\right)\) in an aqueous solution buffered at \(\mathrm{pH}=9.42\).

Which of the following statement(s) is(are) true? a. The alkali metals are found in the earth's crust in the form of pure elements. b. Gallium has one of the highest melting points known for metals. c. When calcium metal reacts with water, one of the products is \(\mathrm{H}_{2}(\mathrm{~g})\) d. When \(\mathrm{AlCl}_{3}\) is dissolved in water, it produces an acidic solution. e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.

What is the hybridization of the underlined nitrogen atom in each of the following molecules or ions? a. \(\underline{N O}^{+}\) b. \(\mathrm{N}_{2} \mathrm{O}_{3}\left(\mathrm{O}_{2} \mathrm{N} \underline{\mathrm{NO}}\right)\) c. \(\underline{N O}_{2}^{-}\) d. \(\underline{N}_{2}\)

Nitrous oxide \(\left(\mathrm{N}_{2} \mathrm{O}\right)\) can be produced by thermal decomposition of ammonium nitrate:$$\mathrm{NH}_{4} \mathrm{NO}_{3}(s) \stackrel{\text { heat}}{\rightarrow} \mathrm{N}_{2} \mathrm{O}(g)+2 \mathrm{H}_{2} \mathrm{O}(l).$$ What volume of \(\mathrm{N}_{2} \mathrm{O}(g)\) collected over water at a total pressure of \(94.0 \mathrm{kPa}\) and \(22^{\circ} \mathrm{C}\) can be produced from thermal decomposition of \(8.68 \mathrm{g} \mathrm{NH}_{4} \mathrm{NO}_{3} ?\) The vapor pressure of water at \(22^{\circ} \mathrm{C}\) is 21 torr.

What is the hybridization of the central atom in each of the following molecules? a. \(\mathrm{SF}_{6}\) b. \(\mathrm{ClF}_{3}\) c. \(\mathrm{GeCl}_{4}\) d. \(\mathrm{XeF}_{4}\)

What is the molecular structure for each of the following molecules or ions? a. \(\mathrm{OCl}_{2}\) b. \(\mathrm{ClO}_{4}^{-}\) c. ICls d. \(\mathrm{PF}_{6}^{-}\)

The atmosphere contains \(9.0 \times 10^{-6 \%}\) Xe by volume at \(1.0 \mathrm{~atm}\) and \(25^{\circ} \mathrm{C}\) a. Calculate the mass of Xe in a room \(7.26 \mathrm{~m}\) by \(8.80 \mathrm{~m}\) by \(5.67 \mathrm{~m}\) b. A typical person takes in about \(2 \mathrm{~L}\) of air during a breath. How many Xe atoms are inhaled in each breath?

Which of following statement(s) is/are true? a. Phosphoric acid is a stronger acid than nitric acid. b. The noble gas with the lowest boiling point is helium. c. Sulfur is found as the free element in the earth's crust. d. One of the atoms in Teffon is fluorine. e. The \(P_{4}\) molecule has a square planar structure.

From the information on the temperature stability of white and gray tin given in this chapter, which form would you expect to have the more ordered structure (have the smaller positional probability)?

Lead forms compounds in the +2 and +4 oxidation states. All lead(II) halides are known (and are known to be ionic). Only \(\mathrm{PbF}_{4}\) and \(\mathrm{PbCl}_{4}\) are known among the possible lead(IV) halides. Presumably lead(IV) oxidizes bromide and iodide ions, producing the lead(II) halide and the free halogen:$$\mathrm{PbX}_{4} \longrightarrow\mathrm{PbX}_{2}+\mathrm{X}_{2}$$. Suppose \(25.00 \mathrm{g}\) of a lead(IV) halide reacts to form \(16.12 \mathrm{g}\) of a lead(II) halide and the free halogen. Identify the halogen.

Many structures of phosphorus-containing compounds are drawn with some \(P=O\) 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.

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 pH of ammonia at this temperature?

Nitrogen gas reacts with hydrogen gas to form ammonia gas \(\left(\mathrm{NH}_{3}\right) .\) Consider the following illustration representing the original reaction mixture in a \(15.0 \mathrm{L}\) container (the numbers of each molecule shown are relative numbers):Assume this reaction mixture goes to completion. The piston apparatus allows the container volume to change in order to keep the pressure constant at 1.00 atm. Assume ideal behavior and constant temperature. 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?

The heaviest member of the alkaline earth metals is radium (Ra), a naturally radioactive element discovered by Pierre and Marie Curie in \(1898 .\) Radium was initially isolated from the uranium ore pitchblende, in which it is present as approximately \(1.0 \mathrm{g}\) per 7.0 metric tons of pitchblende. How many atoms of radium can be isolated from \(1.75 \times 10^{8} \mathrm{g}\) pitchblende (1 metric ton = 1000 kg)? One of the early uses of radium was as an additive to paint so that watch dials coated with this paint would glow in the dark. The longest-lived isotope of radium has a half-life of \(1.60 \times 10^{3}\) years. If an antique watch, manufactured in \(1925,\) contains \(15.0 \mathrm{mg}\) radium, how many atoms of radium will remain in \(2025 ?\)

Indium(III) phosphide is a semiconducting material that has been frequently used in lasers, light-emitting diodes (LED), and fiber-optic devices. This material can be synthesized at900. K according to the following reaction: $$\operatorname{In}\left(\mathrm{CH}_{3}\right)_{3}(g)+\mathrm{PH}_{3}(g) \longrightarrow \operatorname{InP}(s)+3 \mathrm{CH}_{4(g)$$ a. If \(2.56 \mathrm{L} \operatorname{In}\left(\mathrm{CH}_{3}\right)_{3}\) at 2.00 atm is allowed to react with \(1.38 \mathrm{L} \mathrm{PH}_{3}\) at \(3.00 \mathrm{atm},\) what mass of \(\operatorname{In} \mathrm{P}(s)\) will be produced assuming the reaction has an \(87 \%\) yield?b. When an electric current is passed through an optoelectronic device containing InP, the light emitted has an energy of \(2.03 \times 10^{-19} \mathrm{J} .\) What is the wavelength of this light and is it visible to the human eye? c. The semiconducting properties of InP can be altered by doping. If a small number of phosphorus atoms are replaced by atoms with an electron configuration of \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{4},\) is this n-type or \(\mathrm{p}\) -type doping?

Although nitrogen trifluoride (NF \(_{3}\) ) is a thermally stable compound, nitrogen triodide \(\left(\mathrm{NI}_{3}\right)\) 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 \(\mathrm{BN}(s)(-254 \mathrm{kJ} / \mathrm{mol}), \operatorname{IF}(g)(-96 \mathrm{kJ} / \mathrm{mol}),\) 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 moles of IF for every 1 mole of 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?

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 \(\operatorname{Te}(\mathrm{OH})_{6} ?\) 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 $$\operatorname{TeF}_{6}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\operatorname{Te}(\mathrm{OH})_{6}(a q)+6 \mathrm{HF}(a q)$$ Tellurium hexafluoride can be prepared by the reaction of elemental tellurium with fluorine gas:$$\operatorname{Te}(s)+3 \mathrm{F}_{2}(g) \longrightarrow \operatorname{Te} \mathrm{F}_{6}(g)$$.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 L fluorine gas at 1.06 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 \(\operatorname{Te} \mathrm{F}_{6}(g)\) in \(115 \mathrm{mL}\) solution? Assume \(100 \%\) yield in all reactions.

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 the earth was discovered. (4) The Group \(5 \mathrm{A}\) ( 15 ) element in Table \(19-13\) that should have the most metallic character. (5) Symbol of the Group \(6 \mathrm{A}(16)\) 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. (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 smallest noble gas that forms compounds with fluorine having the general formula \(\mathrm{AF}_{2}\) and \(\mathrm{AF}_{4}\) (reverse the symbol 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.