Chapter 21

Properties of the Elements Give examples of two basic oxides. Write equations illustrating the formation of each oxide from its component elements. Write another chemical equation that illustrates the basic character of each oxide.

Give examples of two acidic oxides. Write equations illustrating the formation of each oxide from its component elements. Write another chemical equation that illustrates the acidic character of each oxide.

Give the name and symbol of each element having the valence configuration [noble gas] \(n s^{2} n p^{1}.\)

Give symbols and names for four monatomic ions that have the same electron configuration as argon.

Select one of the alkali metals and write a balanced chemical equation for its reaction with chlorine. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Select one of the alkaline earth metals and write a balanced chemical equation for its reaction with oxygen. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Would you expect to find calcium occurring naturally in the earth's crust as a free element? Why or why not?

Place the following oxides in order of increasing basicity: \(\mathrm{CO}_{2}, \mathrm{SiO}_{2}, \mathrm{SnO}_{2}.\)

Place the following oxides in order of increasing basicity: \(\mathrm{Na}_{2} \mathrm{O}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{SiO}_{2}, \mathrm{SO}_{3}.\)

Complete and balance the equations for the following reactions. [Assume an excess of oxygen for (d).] (a) \(\mathrm{Na}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow\) (b) \(\mathrm{Mg}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\) (c) \(\mathrm{Al}(\mathrm{s})+\mathrm{F}_{2}(\mathrm{g}) \longrightarrow\) (d) \(\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\)

Complete and balance the equations for the following reactions. (a) \(\mathrm{K}(\mathrm{s})+\mathrm{I}_{2}(\mathrm{g}) \longrightarrow\) (b) \(\mathrm{Ba}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\) (c) \(\mathrm{Al}(\mathrm{s})+\mathrm{S}_{8}(\mathrm{s}) \longrightarrow\) (d) \(\mathrm{Si}(\mathrm{s})+\mathrm{Cl}_{2}(\mathrm{g}) \longrightarrow\)

Write balanced chemical equations for the reaction of hydrogen gas with oxygen, chlorine, and nitrogen.

Write an equation for the reaction of potassium and hydrogen. Name the product. Is it ionic or covalent? Predict one physical property and one chemical property of this compound.

A method recently suggested for the preparation of hydrogen (and oxygen) from water proceeds as follows: (a) Sulfuric acid and hydrogen iodide are formed from sulfur dioxide, water, and iodine. (b) The sulfuric acid from the first step is decomposed by heat to water, sulfur dioxide, and oxygen. (c) The hydrogen iodide from the first step is decomposed with heat to hydrogen and iodine. Write a balanced equation for each of these steps and show that their sum is the decomposition of water to form hydro- gen and oxygen.

Compare the mass of \(\mathrm{H}_{2}\) expected from the reaction of steam (H \(_{2} \mathrm{O}\) ) per mole of methane, petroleum, and coal. (Assume complete reaction in each case. Use \(\mathrm{CH}_{2}\) and \(\mathrm{CH}\) as representative formulas for petroleum and coal, respectively.)

Write equations for the reaction of sodium with each of the halogens. Predict at least two physical properties that are common to all of the alkali metal halides.

Write balanced equations for the reaction of lithium, sodium, and potassium with \(\mathrm{O}_{2}\). Specify which metal forms an oxide, which forms a peroxide, and which forms a superoxide.

The electrolysis of aqueous NaCl gives \(\mathrm{NaOH}, \mathrm{Cl}_{2},\) and \(\mathrm{H}_{2}\) (a) Write a balanced equation for the process. (b) In the United States, \(1.19 \times 10^{10} \mathrm{kg}\) of \(\mathrm{NaOH}\) and \(1.14 \times 10^{10} \mathrm{kg}\) of \(\mathrm{Cl}_{2}\) were produced in a recent year. Does the ratio of masses of \(\mathrm{NaOH}\) and \(\mathrm{Cl}_{2}\) produced agree with the ratio of masses expected from the balanced equation? If not, what does this tell you about the way in which \(\mathrm{NaOH}\) and \(\mathrm{Cl}_{2}\) are actually produced? Is the electrolysis of aqueous NaCl the only source of these chemicals?

(a) Write equations for the half-reactions that occur at the cathode and the anode when an aqueous solution of KCl is electrolyzed. Which chemical species is oxidized, and which chemical species is reduced in this reaction? (b) Predict the products formed when an aqueous solution of Csl is electrolyzed.

When magnesium burns in air, it forms both an oxide and a nitride. Write balanced equations for the formation of both compounds.

Calcium reacts with hydrogen gas at \(300400^{\circ} \mathrm{C}\) to form a hydride. This compound reacts readily with water, so it is an excellent drying agent for organic solvents. (a) Write a balanced equation showing the formation of calcium hydride from Ca and \(\mathrm{H}_{2}\) (b) Write a balanced equation for the reaction of calcium hydride with water (Figure 21.6 ).

Name three uses of limestone. Write a balanced equation for the reaction of limestone with \(\mathrm{CO}_{2}\) in water.

Explain what is meant by "hard water." What causes hard water, and what problems are associated with it?

\(\mathrm{Ca}(\mathrm{OH})_{2}\) has a \(K_{* p}\) of \(5.5 \times 10^{-5},\) whereas \(K_{\mathrm{sp}}\) for \(\mathrm{Mg}(\mathrm{OH})_{2}\) is \(5.6 \times 10^{-12} .\) Calculate the equilibrium constant for the reaction \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{Mg}^{2+}(\mathrm{aq}) \rightleftarrows \mathrm{Ca}^{2+}(\mathrm{aq})+\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})\) Explain why this reaction can be used in the commercial isolation of magnesium from sea water.

Diborane can be prepared by the reaction of \(\mathrm{NaBH}_{4}\) and I \(_{2} .\) Which substance is oxidized and which is reduced?

Write equations for the reactions of aluminum with \(\mathrm{HCl}(\mathrm{aq}), \mathrm{Cl}_{2},\) and \(\mathrm{O}_{2}.\)

Aluminum dissolves readily in hot aqueous NaOH to give the aluminate ion, \(\mathrm{Al}(\mathrm{OH})_{4}^{-},\) and \(\mathrm{H}_{2} .\) Write a balanced equation for this reaction. If you begin with \(13.2 \mathrm{g}\) of \(\mathrm{Al}\), what volume (in milliliters) of \(\mathrm{H}_{2}\) gas is produced when the gas is measured at \(735 \mathrm{mm}\) Hg and \(22.5^{\circ} \mathrm{C} ?\)

Alumina, \(A l_{2} O_{3},\) is amphoteric. Among examples of its amphoteric character are the reactions that occur when \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is heated strongly or "fused" with acidic oxides and basic oxides. (a) Write a balanced equation for the reaction of alumina with silica, an acidic oxide, to give aluminum metasilicate, \(\mathrm{Al}_{2}\left(\mathrm{SiO}_{3}\right)_{3}\) (b) Write a balanced equation for the reaction of alumina with the basic oxide CaO to give calcium aluminate, \(\mathrm{Ca}\left(\mathrm{AlO}_{2}\right)_{2}\)

Aluminum sulfate ( 1995 worldwide production is about \(\left.3 \times 10^{9} \mathrm{kg}\right)\) is the most commercially important aluminum compound, after aluminum oxide and aluminum hydroxide. Write a balanced equation for the reaction of aluminum oxide with sulfuric acid to give aluminum sulfate. To manufacture \(1.00 \mathrm{kg}\) of aluminum sulfate, what mass (in kilograms) of aluminum oxide and sulfuric acid must be used?

Gallium hydroxide, like aluminum hydroxide, is amphoteric. (a) Write balanced equations for the reaction of solid \(\mathrm{Ga}(\mathrm{OH})_{3}\) with aqueous \(\mathrm{HCl}\) and \(\mathrm{NaOH}\). (b) What volume of \(0.0112 \mathrm{M} \mathrm{HCl}\) is needed to react completely with \(1.25 \mathrm{g}\) of \(\mathrm{Ga}(\mathrm{OH})_{3} ?\)

Halides of the Group 3 A elements are excellent Lewis acids. When a Lewis base such as \(\mathrm{Cl}^{-}\) interacts with \(\mathrm{AlCl}_{3}\). the ion \(\mathrm{AlCl}_{4}^{-}\) is formed. Draw a Lewis electron dot structure for this ion. What structure is predicted for \(\mathrm{AlCl}_{4}^{-} ?\) What hybridization is assigned to the aluminum atom in \(\mathrm{AlCl}_{4}^{-} ?\)

"Aerated" concrete bricks are widely used building materials. They are obtained by mixing gas-forming additives with a moist mixture of lime, sand, and possibly cement. Industrially, the following reaction is important: $$ \begin{aligned} 2 \mathrm{Al}(\mathrm{s})+3 \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})+6 \mathrm{H}_{2} \mathrm{O}(\ell) & \longrightarrow \\ \left[3 \mathrm{CaO} \cdot \mathrm{Al}_{2} \mathrm{O}_{3} \cdot 6 \mathrm{H}_{2} \mathrm{O}\right](\mathrm{s})+3 \mathrm{H}_{2}(\mathrm{g}) \end{aligned} $$ Assume that the mixture of reactants contains \(0.56 \mathrm{g}\) of \(\mathrm{Al}\) for each brick. What volume of hydrogen gas do you expect at \(26^{\circ} \mathrm{C}\) and atmospheric pressure \((745 \mathrm{mm} \mathrm{Hg}) ?\)

Silicon Describe the structures of \(\mathrm{SiO}_{2}\) and \(\mathrm{CO}_{2}\). Explain why \(\mathrm{SiO}_{2}\) has a very high melting point, whereas \(\mathrm{CO}_{2}\) is a gas.

A major use of hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4},\) is in steam boilers in power plants. (a) The reaction of hydrazine with \(\mathrm{O}_{2}\) dissolved in water gives \(\mathrm{N}_{2}\) and water. Write a balanced equation for this reaction. (b) \(\mathrm{O}_{2}\) dissolves in water to the extent of \(3.08 \mathrm{cm}^{3}\) (gas at STP) in \(100 .\) mL of water at \(20^{\circ} \mathrm{C} .\) To consume all of the dissolved \(\mathrm{O}_{2}\) in \(3.00 \times 10^{4}\) I. of water (enough to fill a small swimming pool), what mass of \(\mathrm{N}_{2} \mathrm{H}_{4}\) is needed?

A common analytical method for hydrazine involves its oxidation with iodate ion, \(10_{3}^{-}\), in acid solution. In the process, hydrazine acts as a four- electron reducing agent. $$ \begin{array}{c} \mathrm{N}_{2}(\mathrm{g})+5 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+4 \mathrm{e}^{-} \longrightarrow \mathrm{N}_{2} \mathrm{H}_{5}^{+}(\mathrm{aq})+5 \mathrm{H}_{2} \mathrm{O}(\ell) \\ E^{\circ}=-0.23 \mathrm{V} \end{array} $$ Write the balanced equation for the reaction of hydrazine in acid solution \(\left(\mathrm{N}_{2} \mathrm{H}_{5}^{+}\right)\) with \(\mathrm{IO}_{3}^{-}(\mathrm{aq})\) to give \(\mathrm{N}_{2}\) and \(\mathrm{I}_{2}\) Calculate \(E^{\circ}\) for this reaction.

Unlike carbon, which can form extended chains of atoms, nitrogen can form chains of very limited length. Draw the Lewis electron dot structure of the azide ion, \(\mathrm{N}_{3}^{-}\).

Review the structure of phosphorous acid in Table 21.7 (a) What is the oxidation number of the phosphorus atom in this acid? (b) Draw the structure of diphosphorous acid, \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{5}\) What is the maximum number of protons this acid can dissociate in water?

Oxygen and Sulfur In the "contact process" for making sulfuric acid, sulfur is first burned to \(\mathrm{SO}_{2}\). Environmental restrictions allow no more than \(0.30 \%\) of this \(\mathrm{SO}_{2}\) to be vented to the atmosphere. (a) If enough sulfur is burned in a plant to produce \(1.80 \times 10^{6} \mathrm{kg}\) of pure, anhydrous \(\mathrm{H}_{2} \mathrm{SO}_{4}\) per day, what is the maximum amount of \(\mathrm{SO}_{2}\) that is allowed to be exhausted to the atmosphere? (b) One way to prevent any \(\mathrm{SO}_{2}\) from reaching the atmosphere is to "scrub" the exhaust gases with slaked lime, \(\mathrm{Ca}(\mathrm{OH})_{2}:\) \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{SO}_{2}(\mathrm{g}) \longrightarrow \mathrm{CaSO}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)\) \(2 \mathrm{CaSO}_{3}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CaSO}_{4}(\mathrm{s})\) What mass of \(\mathrm{Ca}(\mathrm{OH})_{2}\) (in kilograms) is needed to remove the \(\mathrm{SO}_{2}\) calculated in part (a)?

Sulfur forms anionic chains of \(S\) atoms called polysulfides. Draw a Lewis electron dot structure for the \(\mathrm{S}_{2}^{2-}\) ion. The \(\mathrm{S}_{2}^{2-}\) ion is the disulfide ion, an analogue of the peroxide ion. It occurs in iron pyrites, FeS \(_{2}.\)

Sulfur forms a range of compounds with fluorine. Draw Lewis electron dot structures for \(\mathrm{S}_{2} \mathrm{F}_{2}\) (connectivity is FSSF), \(\mathrm{SF}_{2}, \mathrm{SF}_{4}, \mathrm{SF}_{6},\) and \(\mathrm{S}_{2} \mathrm{F}_{10} .\) What is the formal oxidation number of sulfur in each of these compounds?

Halogens combine with one another to produce interhalogens such as \(\mathrm{BrF}\), Sketch a possible molecular structure for this molecule and decide if the \(\mathrm{F}-\mathrm{Br}-\mathrm{F}\) bond angles will be less than or greater than ideal.

Consider the chemistries of the elements sodium, magnesium, aluminum, silicon, and phosphorus. (a) Write a balanced chemical equation depicting the reaction of each element with elemental chlorine. (b) Describe the bonding in each of the products of the reactions with chlorine as ionic or covalent. (c) Draw Lewis electron dot structures for the products of the reactions of silicon and phosphorus with chlorine. What are their electron-pair and molecular geometries?

Consider the chemistries of \(\mathrm{C}, \mathrm{Si},\) Ge, and \(\mathrm{Sn} .\) (a) Write a balanced chemical equation to depict the reaction of each element with elemental chlorine. (b) Describe the bonding in each of the products of the reactions with chlorine as ionic or covalent. (You have not seen reactions of some of these elements in the text, but you have been given enough information to be able to predict the reactions that can occur.)

Complete and balance the following equations. (a) \(\mathrm{KClO}_{3}+\) heat \(\longrightarrow\) (b) \(\mathrm{H}_{2} \mathrm{S}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\) (c) \(\mathrm{Na}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\) (d) \(\mathbf{P}_{4}(s)+\mathbf{K O H}(\mathbf{a q})+\mathbf{H}_{2} \mathbf{O}(\ell) \longrightarrow\) (e) \(\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s})+\) heat \(\longrightarrow\) (f) \(\operatorname{In}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow\) \((g) \operatorname{Sn} \mathrm{Cl}_{4}(\ell)+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow\)

When BCly gas is passed through an electric discharge, small amounts of the reactive molecule \(\mathrm{B}_{2} \mathrm{Cl}_{4}\) are produced. (The molecule has a \(\mathrm{B}\) - B covalent bond.) (a) Draw a Lewis electron dot structure for \(\mathrm{B}_{2} \mathrm{Cl}_{4}\) (b) Describe the hybridization of the \(B\) atoms in the molecule and the geometry around each \(\mathrm{B}\) atom.

(a) Heating barium oxide in pure oxygen gives barium peroxide. Write a balanced equation for this reaction. (b) Barium peroxide is an excellent oxidizing agent. Write a balanced equation for the reaction of iron with barium peroxide to give iron(III) oxide and barium oxide.

Worldwide production of silicon carbide, \(\mathrm{SiC}\), is several hundred thousand tons annually. If you want to produce \(1.0 \times 10^{5}\) metric tons of \(\mathrm{SiC}\), what mass (metric tons) of silicon sand \(\left(\mathrm{Si} \mathrm{O}_{2}\right)\) will you use if \(70 \%\) of the sand is converted to SiC?

One of the pieces of evidence relating to the hydride ion in metal hydrides comes from electrochemistry. Predict the reactions that occur at each electrode when molten LiH is electrolyzed.

To store \(2.88 \mathrm{kg}\) of gasoline with an energy equivalence of \(1.43 \times 10^{8} \mathrm{J}\) requires a volume of \(4.1 \mathrm{L} .\) In comparison, \(1.0 \mathrm{kg}\) of \(\mathrm{H}_{2}\) has the same energy equivalence. What volume is required if this quantity of \(H_{2}\) is to be stored at \(25^{\circ} \mathrm{C}\) and 1.0 atm of pressure?

Halogens form polyhalide ions. Sketch Lewis clectron dot structures and molecular structures for the following ions: (a) \(\mathrm{I}_{3}^{-}\) (b) \(\mathrm{BrCl}_{2}^{-}\) (c) \(\mathrm{ClF}_{2}^{+}\)