Chapter 21

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 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?

Which of the first 10 elements in the periodic table are found as free elements in the earth's crust? Which elements in this group occur in the earth's crust only as part of a chemical compound?

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

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) \(\mathrm{Na}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \rightarrow\) (b) \(\mathrm{Mg}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow\) (c) \(\mathrm{Al}(\mathrm{s})+\mathrm{F}_{2}(\mathrm{g}) \rightarrow\) (d) \(\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow\)

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

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 hydrogen and oxygen.

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

(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 \(300-400^{\circ} \mathrm{C}\) 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 21.7 ).

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?

Calcium oxide, \(\mathrm{CaO},\) is used to remove \(\mathrm{SO}_{2}\) from power plant exhaust. These two compounds react to give solid CaSO \(_{3} .\) What mass of \(\mathrm{SO}_{2}\) can be removed using \(1.2 \times 10^{3} \mathrm{kg}\) of \(\mathrm{CaO} ?\)

\(\mathrm{Ca}(\mathrm{OH})_{2}\) has a \(K_{\mathrm{sp}}\) 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.

Write balanced 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, \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-},\) 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 liters) of \(\mathrm{H}_{2}\) gas is produced when the gas is measured at \(22.5^{\circ} \mathrm{C}\) and a pressure of \(735 \mathrm{mm}\) Hg?

Alumina, \(\mathrm{Al}_{2} \mathrm{O}_{3},\) 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, \(\mathbf{C a}\left(\mathrm{AlO}_{2}\right)_{2}\)

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

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 \(0.0044 \mathrm{g}\) in \(100 .\) mL of water at \(20^{\circ} \mathrm{C} .\) What mass of \(\mathrm{N}_{2} \mathrm{H}_{4}\) is needed to consume all of the dissolved \(\mathbf{O}_{2}\) in 3.00 \(\times 10^{4} \mathrm{L}\) of water (enough to fill a small swimming pool)?

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, \(\mathrm{N}_{3}^{-} .\) Is the ion linear or bent?

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, \(\mathrm{Ca}(\mathrm{OH})_{2}:\) $$\begin{array}{l} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{SO}_{2}(\mathrm{g}) \rightarrow \mathrm{CaSO}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell) \\ 2 \mathrm{CaSO}_{3}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CaSO}_{4}(\mathrm{s}) \end{array}$$ What mass of \(\mathrm{Ca}(\mathrm{OH})_{2}\) (in kilograms) is needed to remove the 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 oxidation number of sulfur in each of these compounds?

The halogen oxides and oxoanions are good oxidizing agents. For example, the reduction of bromate ion has an \(E^{\circ}\) value of \(1.44 \mathrm{V}\) in acid solution: $$2 \mathrm{BrO}_{3}^{-}(\mathrm{aq})+12 \mathrm{H}^{+}(\mathrm{aq})+10 e^{-} \rightarrow{\mathrm{Br}_{2}(\mathrm{aq})}+6 \mathrm{H}_{2} \mathrm{O}(\ell)$$ Is it possible to oxidize aqueous \(1.0 \mathrm{M} \mathrm{Mn}^{2+}\) to aqueous \(\mathrm{MnO}_{4}^{-}\) with \(1.0 \mathrm{M}\) bromate ion?

To prepare chlorine from chloride ion a strong oxidizing agent is required. The dichromate ion, \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-},\) is one example (Figure 21.32 ). Consult the table of standard reduction potentials (Appendix \(\mathbf{M}\) ), and identify several other oxidizing agents that may be suitable. Write balanced equations for the reactions of these substances with chloride ion.

If an electrolytic cell for producing \(\mathrm{F}_{2}\) (Figure 21.31 ) operates at \(5.00 \times 10^{3} \mathrm{A}(\text { at } 10.0 \mathrm{V}),\) what mass of \(\mathrm{F}_{2}\) can be produced per 24 -hour day? Assume the conversion of \(\mathrm{F}^{-}\) to \(\mathrm{F}_{2}\) is \(100 \%\).

Halogens combine with one another to produce interhalogens such as \(\mathrm{BrF}_{3}\). 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 \(\mathrm{C}, \mathrm{Si}, \mathrm{Ge},\) 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. (c) Compare the reactions, if any, of some Group \(4 \mathrm{A}\) chlorides \(-\mathrm{CCl}_{4}, \mathrm{SiCl}_{4},\) and \(\mathrm{SnCl}_{4}-\) with water.

Consider the chemistries of the elements potassium, calcium, gallium, germanium, and arsenic. (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 gallium and arsenic with chlorine. What are their electron-pair and molecular geometries?

When BCl \(_{3}\) 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 \(\mathrm{B}-\mathrm{B}\) covalent bond.) (a) Draw a Lewis electron dot structure for \(\mathbf{B}_{2} \mathrm{Cl}_{4}\) (b) Describe the hybridization of the B atoms in the molecule and the geometry around each \(\mathrm{B}\) atom.

Complete and balance the following equations. (a) \(\mathrm{KClO}_{3}+\) heat \(\rightarrow\) (b) \(\mathrm{H}_{2} \mathrm{S}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow\) (c) \(\mathrm{Na}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow\) (d) \(\mathrm{P}_{4}(\mathrm{s})+\mathrm{KOH}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow\) (e) \(\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s})+\) heat \(\rightarrow\) (f) \(\operatorname{In}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \rightarrow\) (g) \(\mathrm{SnCl}_{4}(\ell)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow\)

(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.

Halogens form polyhalide ions. Sketch Lewis electron dot structures and molecular structures for the following ions: (a) \(\mathrm{I}_{3}^{-}\) (b) \(\mathrm{BrCl}_{2}^{-}\) (c) \(\mathrm{ClF}_{2}^{+}\) (d) An iodide ion and two iodine molecules form the \(\mathrm{I}_{5}^{-}\) ion. Here, the ion has five I atoms in a row, but the ion is not linear. Draw the Lewis dot structure for the ion, and propose a structure for the ion.

Calcium fluoride can be used in the fluoridation of municipal water supplies. If you want to achieve a fluoride ion concentration of \(2.0 \times 10^{-5} \mathrm{M},\) what mass of \(\mathrm{CaF}_{2}\) must you use for \(1.0 \times 10^{6} \mathrm{L}\) of water? \(\left(K_{\mathrm{sp}}\) for \right. \(\left.\mathrm{CaF}_{2} \text { is } 5.3 \times 10^{-11} .\right)\)

The steering rockets in the Space Shuttle use \(\mathrm{N}_{2} \mathrm{O}_{4}\) and a derivative of hydrazine, 1,1 -dimethylhydrazine (page 245 ). This mixture is called a hypergolic fuel because it ignites when the reactants come into contact: $$\begin{aligned} \mathrm{H}_{2} \mathrm{NN}\left(\mathrm{CH}_{3}\right)_{2}(\ell)+2 \mathrm{N}_{2} \mathrm{O}_{4}(\ell) & \rightarrow \\ 3 \mathrm{N}_{2}(\mathrm{g}) &+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})+2 \mathrm{CO}_{2}(\mathrm{g}) \end{aligned}$$ (a) Identify the oxidizing agent and the reducing agent in this reaction. (b) The same propulsion system was used by the Lunar Lander on moon missions in the 1970 s. If the Lander used \(4100 \mathrm{kg}\) of \(\mathrm{H}_{2} \mathrm{NN}\left(\mathrm{CH}_{3}\right)_{2},\) what mass (in kilograms) of \(\mathrm{N}_{2} \mathrm{O}_{4}\) was required to react with it? What mass (in kilograms) of each of the reaction products was generated?

Phosphorus forms an extensive series of oxoanions. (a) Draw a structure, and give the charge for an oxophosphate anion with the formula \(\left[\mathrm{P}_{4} \mathrm{O}_{13}\right]^{\mathrm{n}-} .\) How many ionizable H atoms should the completely protonated acid have? (b) Draw a structure, and give the charge for an oxophosphate anion with the formula \(\left[\mathrm{P}_{4} \mathrm{O}_{12}\right]^{\mathrm{n}-} .\) How many ionizable \(\mathrm{H}\) atoms should the completely protonated acid have?

In \(1774,\) C. Scheele obtained a gas by reacting pyrolusite \(\left(\mathrm{MnO}_{2}\right)\) with sulfuric acid. The gas, which had been obtained that same year by Joseph Priestley by a different method, was an element, A. (a) What is the element isolated by Scheele and Priestley? (b) Element A combines with almost all other elements. For example, with cesium it gives a compound in which the mass percent of \(\mathrm{A}\) is \(19.39 \%\) The element combines with hydrogen to give a compound with a mass percent of element A of 94.12\%. Determine the formulas of the cesium and hydrogen compounds. (c) The compounds of cesium and hydrogen with element A react with one another. Write a balanced equation for the reaction.

What current must be used in a Downs cell operating at \(7.0 \mathrm{V}\) to produce 1.00 metric ton (exactly \(1000 \mathrm{kg}\) ) of sodium per day? Assume \(100 \%\) efficiency.

The chemistry of gallium: (a) Gallium hydroxide, like aluminum hydroxide, is amphoteric. Write a balanced equation to show how this hydroxide can dissolve in both HCl (aq) and \(\mathrm{NaOH}(\mathrm{aq})\) (b) Gallium ion in water, \(\mathrm{Ga}^{3+}(\mathrm{aq}),\) has a \(K_{\mathrm{a}}\) value of \(1.2 \times 10^{-3} .\) Is this ion a stronger or a weaker acid than \(\mathrm{Al}^{3+}(\mathrm{aq}) ?\)

Silicon-oxygen rings are a common structural feature in silicate chemistry. Draw the structure for the anion \(\left[\mathrm{Si}_{3} \mathrm{O}_{9}\right]^{6-},\) which is found in minerals such as benitoite. Is the ring expected to be planar?