Chapter Questions
Although the earth was formed from the same interstellar material as the sun, there is little hydrogen in the earth's atmosphere. How can you explain this?
Hydrogen is produced commercially by the reaction of methane with steam:$$\mathrm{CH}_4(\mathrm{~g})+\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \rightleftharpoons \mathrm{CO}(\mathrm{g})+3 \mathrm{H}_2(\mathrm{~g})$$a. Calculate $\Delta H^{\circ}$ and $\Delta S^{\circ}$ for this reaction (use the data in Appendix 4).b. What temperatures will favor product formation assuming standard conditions and assuming that $\Delta H^{\circ}$ and $\Delta S^{\circ}$ do not depend on temperature?
The major industrial use of hydrogen is in the production of ammonia by the Haber process:$$3 \mathrm{H}_2(g)+\mathrm{N}_2(g) \longrightarrow 2 \mathrm{NH}_3(g)$$a. Using data from Appendix 4 , calculate $\Delta H^{\circ}, \Delta S^{\circ}$, and $\Delta G^{\circ}$ for the Haber process reaction.b. Is this reaction spontaneous at standard conditions?c. At what temperatures is the reaction spontaneous at standard conditions? Assume that $\Delta H^{\circ}$ and $\Delta S^{\circ}$ do not depend on temperature.
List two major industrial uses of hydrogen.
What are the three types of hydrides? How do they differ?
Many lithium salts are hygroscopic (absorb water), but the corresponding salts of the other alkali metals are not. Why are lithium salts different from the others?
․ Complete and balance the following reactions.a. $\mathrm{Rb}(s)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow$b. $\mathrm{Na}_2 \mathrm{O}_2(s)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow$c. $\mathrm{LiH}(s)+\mathrm{H}_2 \mathrm{O}(l)$ $\qquad$d. $\mathrm{KO}_2(s)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow$
Lithium reacts with acetylene in liquid ammonia to produce lithium acetylide ( $\mathrm{LiC} \equiv \mathrm{CH}$ ) and hydrogen gas. Write a balanced equation for this reaction. What type of reaction is this?
What evidence supports putting hydrogen in Group 1A of the periodic table? In some periodic tables hydrogen is listed separately from all of the groups. In what ways is hydrogen unlike a Group 1A element?
The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the second largest consumer of electricity in the United States, after the production of aluminum. Write a balanced equation for the electrolysis of aqueous sodium chloride (hydrogen gas is also produced).
Write balanced equations describing the reaction of lithium metal with each of the following: $\mathrm{O}_2, \mathrm{~S}_8, \mathrm{Cl}_2, \mathrm{P}_4$, $\mathrm{H}_2, \mathrm{H}_2 \mathrm{O}$, and HCl .
Name each of the following compounds.a. $\mathrm{Li}_2 \mathrm{O}$b. $\mathrm{KO}_2$c. $\mathrm{Na}_2 \mathrm{O}_2$
Describe how potassium superoxide can be used in a selfcontained breathing apparatus.
Plot the melting points (Table 18.4) of the alkali metals versus atomic number. Predict the melting point for the element francium. Would you predict francium to be a solid or a liquid at room temperature?
All the Group 1A and 2A metals are produced by electrolysis of molten salts. Why?
Electrolysis of an alkaline earth metal chloride using a current of 5.00 A for 748 seconds deposits 0.471 g of metal at the cathode. What is the identity of the alkaline earth metal chloride?
How does the acidity of the aqueous solutions of the alkaline earth metal ions $\left(\mathrm{M}^{2+}\right)$ change in going down the group?
Predict the geometry around beryllium in the compound $\mathrm{Cl}_2 \mathrm{BeNH}_3$. What hybrid orbitals are used by beryllium and nitrogen in this compound? What type of acid is $\mathrm{BeCl}_2$ ?
Would you expect $\mathrm{BeCl}_2 \mathrm{NH}_3$ or another compound to form from the reaction of $\mathrm{BeCl}_2$ with an excess of am-monia? Draw Lewis structures of other products that might be produced.
Predict a structure of $\mathrm{BeF}_2$ in the gas phase. What structure would you predict for $\mathrm{BeF}_2(s)$ ?
Write balanced equations describing the reaction of Sr with each of the following: $\mathrm{O}_2, \mathrm{~S}_8, \mathrm{Cl}_2, \mathrm{P}_4, \mathrm{H}_2, \mathrm{H}_2 \mathrm{O}$, and HCl .
The compound $\mathrm{BeSO}_4 \cdot 4 \mathrm{H}_2 \mathrm{O}$ cannot be easily dehydrated by heating. It dissolves in water to produce an acidic solution. How do you account for these observations?
One harmful effect of acid rain is the deterioration of structures and statues made of marble or limestone, both of which are essentially calcium carbonate. The reaction of calcium carbonate with sulfuric acid yields carbon dioxide, water, and calcium sulfate. Because calcium sulfate is marginally soluble in water, part of the object is washed away by the rain. Write a balanced chemical equation for the reaction of sulfuric acid with calcium carbonate.
What mass of barium is produced when molten $\mathrm{BaCl}_2$ is electrolyzed by a current of $2.50 \times 10^5 \mathrm{~A}$ for 6.00 h ?
The United States Public Health Service (USPHS) recommends the fluoridation of water as a means for preventing tooth decay. The recommended concentration is 1 mg $\mathrm{F}^{-} /$. The presence of calcium ions in hard water can precipitate the added fluoride. What is the maximum molarity of calcium ions in hard water if the fluoride concentration is at the USPHS recommended level? ( $K_{\mathrm{sp}}$ for $\left.\mathrm{CaF}_2=4.0 \times 10^{-11}.\right)$
Boron hydrides were once evaluated for possible use as rocket fuels. Complete and balance the following reaction:$$\mathrm{B}_2 \mathrm{H}_6+\mathrm{O}_2 \longrightarrow \mathrm{B}(\mathrm{OH})_3$$
Write the formula for each of the following compounds.a. aluminum nitrideb. gallium fluoridec. gallium sulfide
The compound $\mathrm{AlCl}_3$ is quite volatile and appears to exist as a dimer in the gas phase. Propose a structure for this dimer.
Assume that element 113 has been produced. What is the expected electron configuration for element 113? What oxidation states would be exhibited by element 113 in its compounds?
Elemental boron is produced by the reduction of boron oxide by magnesium to give boron and magnesium oxide. Write a balanced equation for this reaction.
$\mathrm{Ga}_2 \mathrm{O}_3$ is an amphoteric oxide and $\mathrm{In}_2 \mathrm{O}_3$ is a basic oxide. Write equations describing reactions that illustrate these properties.
Aluminum hydroxide is amphoteric and will dissolve in both acidic and basic solutions. Write balanced chemical equations representing each process.
What type of semiconductor is formed when a Group 3A element is added as an impurity to Si or Ge ?
Tricalcium aluminate is an important component of Portland cement. It is $44.4 \%$ calcium and $20.0 \%$ aluminum by mass. The remainder is oxygen.a. Calculate the empirical formula of tricalcium aluminate.b. The structure of tricalcium aluminate was not determined until 1975. The aluminate anion $\left(\mathrm{Al}_6 \mathrm{O}_{18}{ }^{18-}\right)$ has the following structure:What is the molecular formula of tricalcium aluminate?c. How would you describe the bonding in the $\mathrm{Al}_6 \mathrm{O}_{18}{ }^{18-}$ anion?
Write equations describing the reactions of Ga with each of the following: $\mathrm{F}_2, \mathrm{O}_2, \mathrm{~S}_8$, and HCl .
Write a balanced equation describing the reaction of aluminum metal with concentrated aqueous sodium hydroxide.
Thallium and indium form +1 and +3 oxidation states when in compounds. Predict the formulas of the possible compounds between thallium and oxygen and between indium and chlorine. Name the compounds.
The inert pair effect is sometimes used to explain the tendency of heavier members of Group 3A to exhibit +1 and +3 oxidation states. What does the inert pair effect reference? (Hint: Consider the valence electron configuration for Group 3A elements.)
Discuss the importance of the $\mathrm{C}-\mathrm{C}$ and $\mathrm{Si}-\mathrm{Si}$ bond strengths and of $\pi$ bonding to the properties of carbon and silicon.
Draw Lewis structures for $\mathrm{CF}_4, \mathrm{GeF}_4$, and $\mathrm{GeF}_6{ }^{2-}$. Predict the molecular structure (including bond angles), and give the expected hybridization of the central atom in these three substances. Explain why $\mathrm{CF}_6{ }^{2-}$ does not form.
Carbon and sulfur form compounds with the formulas $\mathrm{CS}_2$ and $\mathrm{C}_3 \mathrm{~S}_2$. Draw Lewis structures for these compounds and predict the shapes of the molecules.
Why are the tin(IV) halides more volatile than the tin(II) halides?
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?
Silicon is produced for the chemical and electronics industries by the following reactions. Give the balanced equation for each reaction.a. $\mathrm{SiO}_2(\mathrm{~s})+\mathrm{C}(\mathrm{s}) \longrightarrow \mathrm{Si}(\mathrm{s})+\mathrm{CO}(\mathrm{g})$b. Silicon tetrachloride is reacted with very pure magnesium, producing silicon and magnesium chloride.c. $\mathrm{Na}_2 \mathrm{SiF}_6(s)+\mathrm{Na}(s) \longrightarrow \mathrm{Si}(s)+\mathrm{NaF}(s)$
Tin forms compounds in the +2 and +4 oxidation states, Therefore, when tin reacts with flurorine, two products are possible. Write balanced equations for the production of the two tin halide compounds and name them.
Silicon carbide ( SiC ) is an extremely hard substance. Propose a structure for SiC .
Why is graphite a good lubricant? What advantages does it have over grease- or oil-based lubricants?
Write equations describing the reactions of Sn with each of the following: $\mathrm{Cl}_2, \mathrm{O}_2$, and HCl .
The compound $\mathrm{Pb}_3 \mathrm{O}_4$ (red lead) contains a mixture of lead(II) and lead(IV) oxidation states. What is the mole ratio of lead(II) to lead(IV) in $\mathrm{Pb}_3 \mathrm{O}_4$ ?
Calculate the solubility of $\mathrm{Pb}(\mathrm{OH})_2\left(K_{\mathrm{sp}}=1.2 \times 10^{-15}\right)$ in water. Is $\mathrm{Pb}(\mathrm{OH})_2$ more or less soluble in acidic solutions? Explain.
Why are people advised not to drink hot tap water if their plumbing contains lead solder?
In Exercise 96 in Chapter 5, the pressure of $\mathrm{CO}_2$ in a bottle of sparkling wine was calculated assuming that the $\mathrm{CO}_2$ was insoluble in water. This was a bad assumption. Redo this problem by assuming $\mathrm{CO}_2$ obeys Henry's law. Use the data given in that problem to calculate the partial pressure of $\mathrm{CO}_2$ in the gas phase and the solubility of $\mathrm{CO}_2$ in the wine at $25^{\circ} \mathrm{C}$. The Henry's law constant for $\mathrm{CO}_2$ is $3.1 \times 10^{-2} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~atm}^{-1}$ at $25^{\circ} \mathrm{C}$ with Henry's law in the form $\mathrm{C}=k P$, where C is the concentration of the gas in $\mathrm{mol} / \mathrm{L}$.
Lead hydrogen arsenate, an inorganic insecticide used against the potato beetle, is produced by the following reaction:Balance this equation.
The fermentation of glucose produces ethanol and carbon dioxide. Write a balanced equation for this reaction.
Compounds containing the sodide ion $\left(\mathrm{Na}^{-}\right)$have recently been made:$$2 \mathrm{Na}+\text { Crypt } \longrightarrow[\mathrm{Na}(\text { Crypt })]^{+} \mathrm{Na}^{-}$$where Crypt represents a cryptand, $\mathrm{N}\left[\left(\mathrm{C}_2 \mathrm{H}_4 \mathrm{O}\right)_2 \mathrm{C}_2 \mathrm{H}_4\right]_3 \mathrm{~N}$ :The cryptand encapsulates the $\mathrm{Na}^{+}$ion. Why is it necessary to encapsulate $\mathrm{Na}^{+}$?
Ionic compounds, such as $\mathrm{KMnO}_4$, can be dissolved in nonpolar solvents by adding crown ethers. The structure of a typical crown ether is as follows:Suggest how crown ethers make $\mathrm{KMnO}_4$ soluble in nonpolar solvents.
The Group 1A metals are extremely soluble in liquid ammonia, releasing hydrogen gas on dissolution. As the metal begins to dissolve, a deep blue solution forms. The color is attributed to the presence of solvated electrons, or $\mathrm{e}\left(\mathrm{NH}_3\right)_x^{-}$. The metal amide $\left(\mathrm{MNH}_2\right)$ can be isolated by allowing the ammonia to evaporate.a. Write a balanced equation for the formation of $\mathrm{NaNH}_2$.b. The solubility of sodium in liquid ammonia at $-33.5^{\circ} \mathrm{C}$ is $251.4 \mathrm{~g} / \mathrm{kg}$. Calculate the mass percent, mole fraction, and molality of sodium in this solution.
Calculate $\Delta H^{\circ}$ for the reaction$$2 \mathrm{~K}(s)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow 2 \mathrm{KOH}(a q)+\mathrm{H}_2(g)$$
A $5.00-\mathrm{g}$ chunk of potassium is dropped into 1.00 kg of water at $24.0^{\circ} \mathrm{C}$. What is the final temperature of the water after the preceding reaction occurs? Assume that all the heat is used to raise the temperature of the water, and assume that the specific heat capacity of the solution is $4.18 \mathrm{~J}^9 \mathrm{C}^{-1} \mathrm{~g}^{-1}$. (Never run this reaction. It is very dangerous; it bursts into flame!)
Beryllium is amphoteric, in contrast to its fellow Group 2A metals. Beryllium metal reacts with aqueous NaOH to produce hydrogen gas and $\mathrm{Be}(\mathrm{OH})_4{ }^{2-}$. Write a balanced equation for this reaction. What is the oxidizing agent? What is the reducing agent?
Diagonal relationships in the periodic table exist in addition to the vertical relationships. For example, Be and Al are similar in some of their properties, as are B and Si. Rationalize why these diagonal relationships hold for properties such as size, ionization energy, and electron affinity.
In the 1950s and 1960s, several nations conducted tests of nuclear warheads in the atmosphere. It was customary, following each test, to monitor the concentration of strontium-90 (a radioactive isotope of strontium) in milk. Why would strontium- 90 tend to accumulate in milk?
Calculate the pH of a $0.050 \mathrm{M} \mathrm{Al}\left(\mathrm{NO}_3\right)_3$ solution. The $\mathrm{K}_{\mathrm{a}}$ value for $\mathrm{Al}\left(\mathrm{H}_2 \mathrm{O}\right)_6{ }^{3+}$ is $1.4 \times 10^{-5}$.
The compound with the formula $\mathrm{TII}_3$ is a black solid. Given the following standard reduction potentials,$$\begin{aligned}\mathrm{Tl}^{3+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{TI}^{+} & 8^{\circ}=+1.25 \mathrm{~V} \\\mathrm{I}_3^{-}+2 \mathrm{e}^{-} \longrightarrow 3 \mathrm{I}^{-} & \mathrm{g}^{\circ}=+0.55 \mathrm{~V}\end{aligned}$$would you formulate this compound as thallium(III) iodide or thallium(I) triodide?
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.)
The resistivity (a measure of electrical resistance) of graphite is $(0.4$ to 5.0$) \times 10^{-4}$ ohm-cm in the basal plane. (The basal plane is the plane of the six-membered rings of carbon atoms.) The resistivity is 0.2 to 1.0 ohm -cm along the axis perpendicular to the plane. The resistivity of diamond, $10^{14}$ to $10^{16}$ ohm- cm , is independent of direction. How can you account for this behavior in terms of the structures of graphite and diamond?
Dioctyltin compounds are used as stabilizers for polyvinyl chloride polymers. They can be produced by the following reaction:$$\begin{aligned}& 2 \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{X}+\mathrm{Sn} \\& \longrightarrow\left(\mathrm{C}_8 \mathrm{H}_{17}\right)_2 \mathrm{SnX}_2 \\&\end{aligned}$$where X is a halogen. Predict the structure of $\left(\mathrm{C}_8 \mathrm{H}_3\right)_2 \mathrm{SnCl}_2$.
One reason suggested for the instability of long chains of silicon atoms is that the decomposition involves the transition state shown below:The activation energy for such a process is $210 \mathrm{~kJ} / \mathrm{mol}$, which is less than either the $\mathrm{Si}-\mathrm{Si}$ or the $\mathrm{Si}-\mathrm{H}$ bond energy. Why would a similar mechanism not be expected to be very important in the decomposition of long carbon chains?
What are some of the structural differences between quartz and amorphous $\mathrm{SiO}_2$ ?
The bright yellow light emitted by a sodium vapor lamp consists of two emission lines at 589.0 and 589.6 nm . What are the frequency and the energy of a photon of light at each of these wavelengths? What are the energies in $\mathrm{kJ} / \mathrm{mol}$ ?
Use the symbols of the elements described in the following clues to fill in the blanks, which spell the name of a famous American scientist. Although this scientist was better known as a physicist than as a chemist, the Philadelphia institute that bears the scientist's name does include a biochemistry research facility.$$\overline{(1)}-\overline{(2)} \quad \overline{(3)}-\overline{(4)}-\overline{(5)} \overline{(6)}-\overline{(7)}$$(1) The oxide of this metal is amphoteric.(2) You might be surprised to learn that a binary compound of sodium with this element has the formula $\mathrm{NaX}_3$, a compound used in air bags.(3) This alkali metal is radioactive.(4) This element is the alkali metal with the least negative standard reduction potential. Write its symbol in reverse order.(5) Potash is an oxide of this alkali metal.(6) This is the only alkali metal that reacts directly with nitrogen to make a binary compound with formula $\mathrm{M}_3 \mathrm{~N}$.(7) This element is the first in Group 3A for which the +1 oxidation state is exhibited in stable compounds. Use only the second letter of its symbol.
The equilibrium constant for the following reaction is $1.0 \times 10^{23} ;$EDTA is used as a complexing agent in chemical analysis. Solutions of EDTA, usually containing the disodium salt $\mathrm{Na}_2 \mathrm{H}_2$ EDTA, are also used to treat heavy metal poisoning. Calculate $\left[\mathrm{Pb}^{2+}\right]$ at equilibrium in a solution originally 0.0010 M in $\mathrm{Pb}^{2+}$ and 0.050 M in $\mathrm{H}_2$ EDTA $^{2-}$ and buffered at $\mathrm{pH}=6.00$.
Consider dissolving 0.500 mol of $\mathrm{CO}_2(\mathrm{~g})$ to enough water to make a $1.0-\mathrm{L}$ solution. Determine the pH of this solution, and $\left[\mathrm{CO}_3{ }^{2-}\right]$. Use data from Appendix 5, Table 5.2 .
The compounds $\mathrm{CCl}_4$ and $\mathrm{H}_2 \mathrm{O}$ do not react with each other. On the other hand, silicon tetrachloride reacts with water according to the equation$$\mathrm{SiCl}_4(l)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{SiO}_2(s)+4 \mathrm{HCl}(a q)$$
Discuss the importance of thermodynamics and kinetics in the reactivity of water with $\mathrm{SiCl}_4$ as compared with water's lack of reactivity with $\mathrm{CCl}_4$.
Suppose 10.00 g of an alkaline earth metal reacts with 10.0 L of water to produce 6.10 L of hydrogen gas at 1.00 atm and $25^{\circ} \mathrm{C}$. Identify the metal and determine the pH of the solution.
a. Many biochemical reactions that occur in cells require relatively high concentrations of potassium ion ( $\mathrm{K}^{+}$). The concentration of $\mathrm{K}^{+}$in muscle cells is about 0.15 M . The concentration of $\mathrm{K}^{+}$in blood plasma is about 0.0050 M . The high internal concentration in cells is maintained by pumping $\mathrm{K}^{+}$from the plasma. How much work must be done to transport 1.0 mol of $\mathrm{K}^{+}$from the blood to the inside of a muscle cell at $37^{\circ} \mathrm{C}$ (normal body temperature)?b. When 1.0 mol of $\mathrm{K}^{+}$is transferred from blood to the cells, do any other ions have to be transported? Why or why not?c. Cells use the hydrolysis of adenosine triphosphate, abbreviated ATP, as a source of energy. Symbolically, this reaction can be represented as$$\mathrm{ATP}(a q)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{ADP}(a q)+\mathrm{H}_2 \mathrm{PO}_4{ }^{-}(a q)$$where ADP represents adenosine diphosphate. For this reaction at $37^{\circ} \mathrm{C}, K=1.7 \times 10^5$. How many moles of ATP must be hydrolyzed to provide the en-ergy for the transport of 1.0 mol of $\mathrm{K}^{+}$? Assume standard conditions for the ATP hydrolysis reaction.
Suppose 25.00 g of a lead(IV) halide reacts to form 16.12 g of a lead(II) halide and free halogen. Identify the halogen.