Chapter 23

(a) Except for scandium, chromium is the only element in Figure \(23.22\) for which the \(+3\) oxidation state is more stable in general than the \(+2\). Explain why the \(+3\) oxidation state is most characteristic of scandium. (b) What type of magnetism would you expect from \(\mathrm{SrCrO}_{4} ?\) (c) By analogy with inorganic ions of the same formula type, predict the geometrical structure of the permanganate ion, \(\mathrm{MnO}_{4}^{-}\). [Sections 23.7 and 23.8]

Two of the most heavily utilized metals are aluminum and iron. What are the most important natural sources of these elements? In what oxidation state is each metal found in nature?

(a) Pyrolusite \(\left(\mathrm{MnO}_{2}\right)\) is a commercially important mineral of manganese. What is the oxidationstate of \(\mathrm{Mn}\) in this metal? (b) Name some reagents that might be used to reduce this ore to the metal.

Explain in your own words what is meant by the statement, "This ore consists of a small concentration of chalcopyrite, together with considerable gangue."

What is meant by the following terms: (a) calcination, (b) leaching, (c) smelting, (d) slag?

Complete and balance each of the following equations: (a) \(\mathrm{Cr}_{2} \mathrm{O}_{3}(s)+\mathrm{Na}(l) \longrightarrow\) (b) \(\mathrm{PbCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}\) (c) \(\mathrm{CdS}(s)+\mathrm{O}_{2}(g) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{ZnO}(\mathrm{s})+\mathrm{CO}(g) \stackrel{\Delta}{\longrightarrow}\)

Complete and balance each equation: (a) \(\mathrm{PbS}(s)+\mathrm{O}_{2}(g) \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{CoCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}\) (c) \(\mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{VCl}_{3}(g)+\mathrm{K}(l) \longrightarrow\) (e) \(\mathrm{BaO}(s)+\mathrm{P}_{2} \mathrm{O}_{5}(l) \longrightarrow\)

A sample containing \(\mathrm{PbSO}_{4}\) is to be refined to \(\mathrm{Pb}\) metal via calcination, followed by roasting. (a) What volatile product would you expect to be produced by calcination? (b) Propose an appropriate atmosphere to accompany the roasting. (c) Write balanced chemical equations for the steps.

Consider the thermodynamics of calcination. (a) The following equation is a generic reaction representing calcination of a metal carbonate: $$\mathrm{MCO}_{3}(s) \longrightarrow \mathrm{MO}(s)+\mathrm{CO}_{2}(g)$$ Would you expect this reaction to become more or less spontaneous as the temperature increases? (b) What is the standard free energy, \(\Delta G^{\circ}\), for the reaction corresponding to the calcination of \(\mathrm{PbCO}_{3}\) (Equation 23.1) at \(25^{\circ} \mathrm{C}\) under standard conditions? Is this reaction spontaneous? If not, at what temperature does this reaction become spontaneous (assuming \(\Delta H^{\circ}\) and \(S^{\circ}\) values do not change with temperature)?

Assess the feasibility of reducing \(\mathrm{TiO}_{2}\) to titanium metal by roasting in carbon monoxide. (a) Write a reaction for this process. (b) Use the thermodynamic quantities given in Appendix \(C\) to calculate \(\Delta G^{\circ}, \Delta H^{\circ}\), and \(\Delta S^{\circ}\) for this reaction. Is this reaction spontaneous at \(25^{\circ} \mathrm{C}\) under standard conditions? (c) If we assume that \(\Delta H^{\circ}\) and \(S^{\circ}\) values do not change with temperature, at what temperature would this process become spontaneous? Do you think this process would be practical?

What is the major reducing agent in the reduction of iron ore in a blast furnace? Write a balanced chemical equation for the reduction process.

Write balanced chemical equations for the reduction of \(\mathrm{FeO}\) and \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) by \(\mathrm{H}_{2}\) and by \(\mathrm{CO}\).

What role does each of the following materials play in the chemical processes that occur in a blast furnace: (a) air, (b) limestone, \((c)\) coke, \((\) d) water? Write balanced chemical equations to illustrate your answers.

(a) In the basic oxygen process for steel formation, what reactions cause the temperature in the converter to increase? (b) Write balanced chemical equations for the oxidation of carbon, sulfur, and silicon in the converter.

Describe how electrometallurgy could be employed to purify crude cobalt metal. Describe the compositions of the electrodes and electrolyte, and write out all electrode reactions.

The element tin is generally recovered from deposits of the ore cassiterite \(\left(\mathrm{SnO}_{2}\right)\). The oxide is reduced with carbon, and the crude metal is purified by electrolysis. Write balanced chemical equations for the reduction process and for the electrode reactions in the electrolysis. (Assume that an acidic solution of \(\mathrm{SnSO}_{4}\) is employed as an electrolyte in the electrolysis.)

Sodium is a highly malleable substance, whereas sodium chloride is not. Explain this difference in properties.

Germanium has the same crystal structure as diamond (Figure 11.41). Based on this fact, do you think germanium is likely to exhibit metallic properties? Explain your answer.

Explain how the electron-sea model accounts for the high electrical and thermal conductivity of metals.

(a) Compare the electronic structures of atomic chromium and atomic selenium. In what respects are they similar, and in what respects do they differ? (b) Chromium is a metal, and selenium is a nonmetal. What factors are important in determining this difference in properties?

The densities of the elements \(\mathrm{K}, \mathrm{Ca}, \mathrm{Sc}\), and \(\mathrm{Ti}\) are \(0.86\), 1.5, 3.2, and \(4.5 \mathrm{~g} / \mathrm{cm}^{3}\), respectively. What factors are likely to be of major importance in determining this variation? Which factor do you think will be the most important?

Which would you expect to be the more ductile element, (a) Ag or Mo, (b) Zn or Si? In each case explain your reasoning.

How do you account for the observation that the alkali metals, like sodium and potassium, are soft enough to be cut with a knife?

Tin exists in two allotropic forms: Gray tin has a diamond structure, and white tin has a close-packed structure. One of these allotropic forms is a semiconductor with a small band gap while the other is a metal. Which one is which? Which form would you expect to have the longer Sn \(-\mathrm{Sn}\) bond distance?

The electrical conductivity of titanium is approximately 2500 times greater than that of silicon. Titanium has a hexagonal close-packed structure, and silicon has the diamond structure. Explain how the structures relate to the relative electrical conductivities of the elements.

Define the term alloy. Distinguish among solution alloys, heterogeneous alloys, and intermetallic compounds.

Distinguish between substitutional and interstitial alloys. What conditions favor formation of substitutional alloys?

For each of the following alloy compositions indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) \(\mathrm{Fe}_{0.97} \mathrm{Si}_{0.03}\), (b) \(\mathrm{Fe}_{0.60} \mathrm{Ni}_{0,40}\), (c) \(\mathrm{Cu}_{3} \mathrm{~A} \mathbf{u}\).

For each of the following alloy compositions indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) \(\mathrm{Cu}_{0.66} \mathrm{Zn}_{0.34}\) (b) \(\mathrm{Ag}_{3} \mathrm{Sn}\), (c) \(\mathrm{Ti}_{0.99} \mathrm{O}_{0.01}\).

Which of the following properties are better considered characteristic of the free isolated atoms, and which are characteristic of the bulk metal: (a) electrical conductivity, (b) first ionization energy, (c) atomic radius, (d) melting point, (e) heat of vaporization, (f) electron affinity?

Which of the following species would you expect to possess metallic properties: (a) \(\mathrm{TiCl}_{4}\), (b) NiCo alloy,(c) \(\mathrm{W}\), \(\mathrm{d}\) ) \(\mathrm{Ge}\), (e) \(\mathrm{Hg}_{2}{\underline{\phantom{xx}}}^{2+}\) ? Explain in each case.

Zirconium and hafnium are the group \(4 \mathrm{~B}\) elements in the second and third transition series. The radii of these elements are virtually the same (Figure 23.20). Explain this similarity.

What is meant by the term lanthanide contraction? What properties of the transition elements are affected by the lanthanide contraction?

Write the formula for the fluoride corresponding to the highest expected oxidation state for (a) \(\mathrm{Sc}\), (b) \(\mathrm{Co}\), (c) \(\mathrm{Zn}\), (d) Mo.

Write the formula for the oxide corresponding to the highest expected oxidation state for (a) \(\mathrm{Cd},(\mathrm{b}) \mathrm{V},(\mathrm{c}) \mathrm{W},(\mathrm{d}) \mathrm{Ru}\).

Why does chromium exhibit several oxidation states in its compounds, whereas aluminum exhibits only the \(+3\) oxidation state?

The element vanadium exhibits multiple oxidation states in its compounds, including \(+2\). The compound \(\mathrm{VCl}_{2}\) is known, whereas \(\mathrm{ScCl}_{2}\) is unknown. Use electron configurations and effective nuclear charges to account for this difference in behavior.

Write the expected electron configuration for (a) \(\mathrm{Cr}^{3+}\), (b) \(\mathrm{Au}^{3+}, (\mathrm{c}) \mathrm{Ru}^{2+}\) (d) \(\mathrm{Cu}^{+}\), (e) \(\mathrm{Mn}^{4+},(\mathrm{f}) \mathrm{Ir}^{+}\)

What is the expected electron configuration for (a) \(\mathrm{Ti}^{2+}\), (b) \(\mathrm{Co}^{3+}\) (c) \(\mathrm{Pd}^{2+}\) (d) \(\mathrm{Mo}^{3+}\), (e) \(\mathrm{Ru}^{3+}\), (f) \(\mathrm{Ni}^{4+}\) ?

Which would you expect to be more easily oxidized, \(\mathrm{Ti}^{2+}\) or \(\mathrm{Ni}^{2+} ?\)

Which would you expect to be the stronger reducing agent, \(\mathrm{Cr}^{2+}\) or \(\mathrm{Fe}^{2+} ?\)

How does the presence of air affect the relative stabilities of ferrous and ferric ions in solution?

(a) Give the chemical formulas and colors of the chromate and dichromate ions. (b) Which of these ions is more stable in acidic solution? (c) What type of reaction is involved in their interconversion in solution?

Write balanced chemical equations for the reaction between iron and (a) hydrochloric acid, (b) nitric acid.

\(\mathrm{MnO}_{2}\) reacts with aqueous \(\mathrm{HCl}\) to yield \(\mathrm{MnCl}_{2}(a q)\) and chlorine gas. (a) Write a balanced chemical equation for the reaction. (b) Is this an oxidation-reduction reaction? If yes, identify the oxidizing and reducing agents.

On the atomic level, what distinguishes a paramagnetic material from a diamagnetic one? How does each behave in a magnetic field?

On the atomic level, what distinguishes an antiferromagnetic material from a diamagnetic one?

(a) On the atomic level, what distinguishes ferromagnetic, ferrimagnetic, and antiferromagnetic materials from each other? (b) Which one of these types of magnetic materials cannot be used to make a permanent magnet?

The two most important iron oxide minerals are magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4}\), and hematite, \(\mathrm{Fe}_{2} \mathrm{O}_{3}\). One is a ferrimagnetic material, while the other is an antiferromagnetic material. (a) Based on the oxidation states of iron, which one is more likely to be ferrimagnetic? (b) Would it be possible to use magnetic fields to separate these minerals?

Write a chemical equation for the reaction that occurs when \(\mathrm{PbS}\) is roasted in air. Why might a sulfuric acid plant be located near a plant that roasts sulfide ores?