General Chemistry: Principles and Modern Applications

Ralph H. Petrucci, F. Geoffrey Herring, Jeffry D. Madura

Chapter 23

The Transition Elements - all with Video Answers

Educators

Chapter Questions

Problem 1

By means of orbital diagrams, write electron configurations for the following transition element atom and ions: $(a) \mathrm{Ti} ;(\mathbf{b}) \mathrm{V}^{3+} ;(\mathrm{c}) \mathrm{Cr}^{2+} ;(\mathrm{d}) \mathrm{Mn}^{4+} ;(\mathrm{e}) \mathrm{Mn}^{2+} ;(\mathrm{f}) \mathrm{Fe}^{3+}$.

Lottie Adams

Lottie Adams

Numerade Educator

Problem 2

Arrange the following species according to the number of unpaired electrons they contain, starting with the one that has the greatest number: $\mathrm{Fe}, \mathrm{Sc}^{3+}, \mathrm{Ti}^{2+}$ $\mathrm{Mn}^{4+}, \mathrm{Cr}, \mathrm{Cu}^{2+}$.

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 3

Describe how the transition elements compare with main-group metals (such as group 2 ) with respect to oxidation states, formation of complexes, colors of compounds, and magnetic properties.

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 4

With only minor irregularities, the melting points of the first series of transition metals rise from that of Sc to that of Cr and then fall to that of Zn. Give a plausible explanation for this phenomenon based on atomic structure.

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 5

Why do the atomic radii vary so much more for two main-group elements that differ by one unit in atomic number than they do for two transition elements that differ by one unit?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 6

The metallic radii of $\mathrm{Ni}$, $\mathrm{Pd}$, and $\mathrm{Pt}$ are $125,138,$ and
$139 \mathrm{pm},$ respectively. Why is the difference in radius between Pt and Pd so much less than between Pd and Ni?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 7

Which of the first transition series elements exhibits the greatest number of different oxidation states in its compounds? Explain.

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 8

Why is the number of common oxidation states for the elements at the beginning and those at the end of the first transition series less than for elements in the middle of the series?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 9

As a group, the lanthanides are more reactive metals than are those in the first transition series. How do you account for this difference?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 10

The maximum difference in standard reduction potential, $E_{\mathrm{M}}^{\circ} 2^{2+} / \mathrm{M}(\mathrm{s}),$ among members of the first transition series is about 2.4 V. For the lanthanides, the maximum difference in $E_{\mathrm{M}}^{\circ} 3^{3+} / \mathrm{M}(\mathrm{s})$ is only about $0.4 \mathrm{V}$ How do you account for this fact?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 11

Complete and balance the following equations. If no reaction occurs, so state.
(a) $\operatorname{TiCl}_{4}(\mathrm{g})+\mathrm{Na}(1) \stackrel{\Delta}{\longrightarrow}$
(b) $\mathrm{Cr}_{2} \mathrm{O}_{3}(\mathrm{s})+\mathrm{Al}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}$
(c) $\mathrm{Ag}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow$
(d) $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})+\mathrm{KOH}(\mathrm{aq}) \longrightarrow$
(e) $\mathrm{MnO}_{2}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}$

Lottie Adams

Numerade Educator

Problem 12

By means of a chemical equation, give an example to represent the reaction of (a) a transition metal with a nonoxidizing acid; (b) a transition metal oxide with $\mathrm{NaOH}(\mathrm{aq}) ;(\mathrm{c})$ an inner transition metal with $\mathrm{HCl}(\mathrm{aq})$.

Vishal Sharma

Numerade Educator

Problem 13

Write balanced chemical equations for the following reactions described in the chapter.
(a) the reaction of $\operatorname{Sc}(\text { OH })_{3}(\text { s) with } \mathrm{HCl}(\text { aq })$
(b) oxidation of $\mathrm{Fe}^{2+}(\mathrm{aq})$ by $\mathrm{MnO}_{4}^{-}(\text {aq })$ in basic solution to give $\mathrm{Fe}^{3+}(\mathrm{aq})$ and $\mathrm{MnO}_{2}(\mathrm{s})$
(c) the reaction of $\mathrm{TiO}_{2}(\mathrm{s})$ with molten $\mathrm{KOH}$ to form $\mathrm{K}_{2} \mathrm{TiO}_{3}$.
(d) oxidation of $\mathrm{Cu}(\mathrm{s})$ to $\mathrm{Cu}^{2+}(\mathrm{aq})$ with $\mathrm{H}_{2} \mathrm{SO}_{4}$
(concd aq) to form $\mathrm{SO}_{2}(\mathrm{g})$.

Vishal Sharma

Numerade Educator

Problem 14

Write balanced equations for the following reactions described in the chapter.
(a) $\operatorname{Sc}(\text { l) is produced by the electrolysis of } \mathrm{Sc}_{2} \mathrm{O}_{3}$ dis solved in $\mathrm{Na}_{3} \mathrm{ScF}_{6}(1)$
(b) Cr(s) reacts with HCl(aq) to produce a blue solution containing $\mathrm{Cr}^{2+}(\mathrm{aq})$
(c) $\mathrm{Cr}^{2+}(\text { aq })$ is readily oxidized by $\mathrm{O}_{2}(\mathrm{g})$ to $\mathrm{Cr}^{3+}(\mathrm{aq})$
(d) $\mathrm{Ag}(\mathrm{s})$ reacts with concentrated $\mathrm{HNO}_{3}(\mathrm{aq}),$ and $\mathrm{NO}_{2}(\mathrm{g})$ is evolved.

Lottie Adams

Numerade Educator

Problem 15

Suggest a series of reactions, using common chemicals, by which each of the following syntheses can be performed.
(a) $\operatorname{Fe}(\text { OH })_{3}(\text { s) from } \operatorname{Fe} S( \text { s) }$
(b) $\mathrm{BaCrO}_{4}(\mathrm{s})$ from $\mathrm{BaCO}_{3}(\mathrm{s})$ and $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})$

Lottie Adams

Numerade Educator

Problem 16

Suggest a series of reactions, using common chemicals, by which each of the following syntheses can be performed.
(a) $\mathrm{Cu}(\mathrm{OH})_{2}(\mathrm{s})$ from $\mathrm{CuO}(\mathrm{s})$
(b) $\operatorname{Cr} \mathrm{Cl}_{3}\left(\text { aq) } \text { from }\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{s})\right.$

Vishal Sharma

Numerade Educator

Problem 17

One of the simplest metals to extract from its ores is mercury. Mercury vapor is produced by roasting cinnabar ore (HgS) in air. Alternatives to this simple roasting, designed to reduce or eliminate $\mathrm{SO}_{2}$ emissions, is to roast the ore in the presence of a second substance. For example, when cinnabar is roasted with quicklime, the products are mercury vapor and calcium sulfide and calcium sulfate. Write equations for the two reactions described here.

Vishal Sharma

Numerade Educator

Problem 18

According to Figure $23-8, \Delta G^{\circ}$ decreases with temperature for the reaction $2 \mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CO}(\mathrm{g})$
How would you expect $\Delta G^{\circ}$ to vary with temperature for the following reactions?
(a) $\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{g})$
(b) $2 \mathrm{CO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CO}_{2}(\mathrm{g})$

Lottie Adams

Numerade Educator

Problem 19

Calcium will reduce $\mathrm{MgO}(\mathrm{s})$ to $\mathrm{Mg}(\mathrm{s})$ at all temperatures from 0 to $2000^{\circ} \mathrm{C}$. Use this fact, together with the melting point ( $839^{\circ} \mathrm{C}$ ) and boiling point $\left(1484^{\circ} \mathrm{C}\right)$ of calcium, to sketch a plausible graph of $\Delta G^{\circ}$ as a function of temperature for the reaction $2 \mathrm{Ca}(\mathrm{s})+$ $\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CaO}(\mathrm{s})$.

Lottie Adams

Numerade Educator

Problem 20

One method of obtaining chromium metal from chromite ore is as follows. After reaction (23.16) sodium chromate is reduced to chromium(III) oxide by carbon. Then the chromium(III) oxide is reduced to chromium metal by silicon. Write plausible equations to describe these two reactions.

Vishal Sharma

Numerade Educator

Problem 21

Write plausible half-equations to represent each of the following in acidic solution.
(a) $\mathrm{VO}^{2+}(\mathrm{aq})$ as an oxidizing agent
(b) $\mathrm{Cr}^{2+}(\text { aq })$ as a reducing agent

Lottie Adams

Numerade Educator

Problem 22

Write plausible half-equations to represent each of the following in basic solution.
(a) oxidation of $\mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})$ to $\mathrm{FeO}_{4}^{2-}$
(b) reduction of $\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]^{-}$ to silver metal

Vishal Sharma

Numerade Educator

Problem 23

Use electrode potential data from this chapter or Appendix D to predict whether each of the following reactions will occur to any significant extent under standard-state conditions.
$$\begin{aligned}
&\text { (a) } 2 \mathrm{VO}_{2}^{+}+6 \mathrm{Br}^{-}+8 \mathrm{H}^{+} \longrightarrow\\
&&2 \mathrm{V}^{2+}+3 \mathrm{Br}_{2}(1)+4 \mathrm{H}_{2} \mathrm{O}
\end{aligned}$$
$$\text { (b) } \mathrm{VO}_{2}^{+}+\mathrm{Fe}^{2+}+2 \mathrm{H}^{+} \longrightarrow \mathrm{VO}^{2+}+\mathrm{Fe}^{3+}+\mathrm{H}_{2} \mathrm{O}$$
$$\begin{aligned}
&\text { (c) } \mathrm{MnO}_{2}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}_{2}+2 \mathrm{H}^{+} \longrightarrow\\
&&\mathrm{Mn}^{2+}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}(\mathrm{g})
\end{aligned}$$

Vishal Sharma

Numerade Educator

Problem 24

You are given these three reducing agents: $\mathrm{Zn}(\mathrm{s})$ $\mathrm{Sn}^{2+}(\mathrm{aq}),$ and $\mathrm{I}^{-}(\mathrm{aq}) .$ Use data from Appendix $\mathrm{D}$ to
determine which of them can, under standard-state conditions in acidic solution, reduce
(a) $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$ to $\mathrm{Cr}^{3+}(\mathrm{aq})$
(b) $\mathrm{Cr}^{3+}(\text { aq })$ to $\mathrm{Cr}^{2+}(\mathrm{aq})$
(c) $\mathrm{SO}_{4}^{2-}(\text { aq })$ to $\mathrm{SO}_{2}(\mathrm{g})$

Emily Marty

Numerade Educator

Problem 25

Refer to Example $23-2 .$ Select a reducing agent (from Table 23.1 or Appendix D) that will reduce VO $^{2+}$ to $\mathrm{V}^{3+}$ and no further in acidic solution.

Lottie Adams

Numerade Educator

Problem 26

The electrode potential diagram for manganese in acidic solutions in Figure $23-14$ does not include a value of $E^{\circ}$ for the reduction of $\mathrm{MnO}_{4}^{-}$ to $\mathrm{Mn}^{2+}$. Use other data in the figure to establish this $E^{\circ},$ and $\mathrm{com}-$ pare your result with the value found in Table 20.1.

Lottie Adams

Numerade Educator

Problem 27

Use data from the text to construct a standard electrode potential diagram relating the following chromium species in acidic solution.

Lottie Adams

Numerade Educator

Problem 28

Use data from the text to construct a standard electrode potential diagram relating the following vanadium species in acidic solution.

Lottie Adams

Numerade Educator

Problem 29

When a soluble lead compound is added to a solution containing primarily orange dichromate ion, yellow lead chromate precipitates. Describe the equilibria involved.

Vishal Sharma

Numerade Educator

Problem 30

When yellow $\mathrm{BaCrO}_{4}$ is dissolved in $\mathrm{HCl}(\mathrm{aq}),$ a green solution is obtained. Write a chemical equation to account for the color change.

Vishal Sharma

Numerade Educator

Problem 31

When $\mathrm{Zn}(\mathrm{s})$ is added to $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ dissolved in $\mathrm{HCl}(\mathrm{aq}),$ the color of the solution changes from orange to green, then to blue, and, over a period of time, back to green. Write equations for this series of reactions.

Vishal Sharma

Numerade Educator

Problem 32

If $\mathrm{CO}_{2}(\mathrm{g})$ under pressure is passed into $\mathrm{Na}_{2} \mathrm{CrO}_{4}(\mathrm{aq})$
$\mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})$ is formed. What is the function of
the $\mathrm{CO}_{2}(\mathrm{g}) ?$ Write a plausible equation for the net reaction.

Vishal Sharma

Numerade Educator

Problem 33

Use equation (23.19) to determine $\left[\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\right]$ in a solution that has $\left[\mathrm{CrO}_{4}^{2-}\right]=0.20 \mathrm{M}$ and a pH of (a) 6.62 and (b) 8.85.

Lottie Adams

Numerade Educator

Problem 34

If a solution is prepared by dissolving $1.505 \mathrm{g}$ $\mathrm{Na}_{2} \mathrm{CrO}_{4}$ in $345 \mathrm{mL}$ of a buffer solution with $\mathrm{pH}=7.55,$ what will be $\left[\mathrm{CrO}_{4}^{2-}\right]$ and $\left[\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\right] ?$

Lottie Adams

Numerade Educator

Problem 35

How many grams of chromium would be deposited on an object in a chrome-plating bath (see page 1048 ) after
$1.00 \mathrm{h}$ at a current of $3.4 \mathrm{A} ?$

Lottie Adams

Numerade Educator

Problem 36

How long would an electric current of 3.5 A have to pass through a chrome-plating bath (see page 1048 ) to produce a chromium deposit $0.0010 \mathrm{mm}$ thick on an object with a surface area of $0.375 \mathrm{m}^{2}$ ? (The density of Cris $7.14 \mathrm{g} \mathrm{cm}^{-3}$.

Lottie Adams

Numerade Educator

Problem 37

Why is it reasonable to expect the chemistry of dichromate ion to involve mainly oxidation-reduction reactions and that of chromate ion to involve mainly precipitation reactions?

Vishal Sharma

Numerade Educator

Problem 38

What products are obtained when $\mathrm{Mg}^{2+}(\mathrm{aq})$ and $\mathrm{Cr}^{3+}(\mathrm{aq})$ are each treated with a limited amount of NaOH(aq)? With an excess of $\mathrm{NaOH}($ aq)? Why are the results different in these two cases?

Vishal Sharma

Numerade Educator

Problem 39

Will reaction (23.25) still be spontaneous in the forward direction in a solution containing equal concentrations of $\mathrm{Fe}^{2+}$ and $\mathrm{Fe}^{3+},$ a pH of $3.25,$ and under an $\mathrm{O}_{2}(\mathrm{g})$ partial pressure of 0.20 atm?

Vishal Sharma

Numerade Educator

Problem 40

Based on the description of the nickel-cadmium cell on page $1053,$ and with appropriate data from Appendix $D$, estimate $E^{\circ}$ for the reduction of $\mathrm{NiO}(\mathrm{OH})$ to $\mathrm{Ni}(\mathrm{OH})_{2}$

Lottie Adams

Numerade Educator

Problem 41

Write a net ionic equation to represent the precipitation of Prussian blue, described on page 1053 .

Lottie Adams

Numerade Educator

Problem 42

The reaction to form Turnbull's blue (page 1053 ) appears to occur in two stages. First, $\mathrm{Fe}^{2+}(\mathrm{aq})$ is oxidized to $\mathrm{Fe}^{3+}(\mathrm{aq})$ and ferricyanide ion is reduced to ferrocyanide ion. Then, the $\mathrm{Fe}^{3+}(\text { aq })$ and ferrocyanide ion combine. Write equations for these reactions.

Lottie Adams

Numerade Educator

Problem 43

Write plausible equations for the following reactions occurring in the hydrometallurgy of the coinage metals.
(a) Copper is precipitated from a solution of copper(II) sulfate by treatment with $\mathrm{H}_{2}(\mathrm{g})$
(b) Gold is precipitated from a solution of $\mathrm{Au}^{+}$ by adding iron(II) sulfate.
(c) Copper(II) chloride solution is reduced to copper(I) chloride when treated with $\mathrm{SO}_{2}(\mathrm{g})$ in acidic solution.

Vishal Sharma

Numerade Educator

Problem 44

In the metallurgical extraction of silver and gold, an alloy of the two metals is often obtained. The alloy can be separated into Ag and Au either with concentrated $\mathrm{HNO}_{3}$ or boiling concentrated $\mathrm{H}_{2} \mathrm{SO}_{4},$ in a process called parting. Write chemical equations to show how these separations work.

Vishal Sharma

Numerade Educator

Problem 45

Use the result of the Integrative Example to determine whether a solution can be prepared with $\left[\mathrm{Cu}^{+}\right]$ equal to (a) $0.20 \mathrm{M} ;$ (b) $1.0 \times 10^{-10} \mathrm{M}$.

Lottie Adams

Numerade Educator

Problem 46

Show that the corrosion reaction in which Cu is converted to its basic carbonate (reaction 23.27 ) can be thought of in terms of a combination of oxidationreduction, acid-base, and precipitation reactions.

Vishal Sharma

Numerade Educator

Problem 47

Use data from Table 23.8 to determine $E^{\circ}$ for the reduction of $\mathrm{Hg}^{2+}$ to $\mathrm{Hg}_{2}^{2+}$ in aqueous solution.

Vishal Sharma

Numerade Educator

Problem 48

At $400^{\circ} \mathrm{C}, \Delta G^{\circ}=-25 \mathrm{kJ}$ for the reaction $2 \mathrm{Hg}(1)+$
$\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{HgO}(\mathrm{s}) .$ If a sample of $\mathrm{HgO}(\mathrm{s})$ is heated
to $400^{\circ} \mathrm{C},$ what will be the equilibrium partial pressure of $\mathrm{O}_{2}(\mathrm{g}) ?$

Lottie Adams

Numerade Educator

Problem 49

Use Figure $23-8$ to estimate for the reaction $\mathrm{ZnO}(\mathrm{s})+$ $\mathrm{C}(\mathrm{s}) \rightleftharpoons \mathrm{Zn}(1)+\mathrm{CO}(\mathrm{g}),$ at about $800^{\circ} \mathrm{C},$ (a) a value
of $K_{p}$ and $(b)$ the equilibrium pressure of $C O(g)$.

Lottie Adams

Numerade Educator

Problem 50

The vapor pressure of $\mathrm{Hg}(1)$ as a function of temperature is $\log P(\mathrm{mmHg})=(-0.05223 a / T)+b,$ where
$a=61,960$ and $b=8.118 ; T$ is the Kelvin temperature.
Show that at $25^{\circ} \mathrm{C}$, the concentration of $\mathrm{Hg}(\mathrm{g})$ in equilibrium with Hg(l) greatly exceeds the maximum permissible level of $0.05 \mathrm{mg} \mathrm{Hg} / \mathrm{m}^{3}$ air.

Madi Sousa

Numerade Educator

Problem 51

In $\mathrm{ZnO}$, the band gap between the valence and conduction bands is $290 \mathrm{kJmol}^{-1}$, and in $\mathrm{CdS}$ it is $250 \mathrm{kJmol}^{-1} .$ Show that CdS absorbs some visible light but ZnO does not. Explain the observed colors:
$\mathrm{ZnO}$ is white and $\mathrm{CdS}$ is yellow.

Lottie Adams

Numerade Educator

Problem 52

CdS is yellow, HgS is red, and CdSe is black. Which of these materials has the largest band gap? the smallest? How does the band gap relate to the observed color?

Emily Marty

Numerade Educator

Problem 53

Although Au reacts with and dissolves in aqua regia (3 parts $\mathrm{HCl}+1$ part $\mathrm{HNO}_{3}$ ), Ag does not dissolve. What is (are) the likely reason(s) for this difference?

Vishal Sharma

Numerade Educator

Problem 54

The text mentions that scandium metal is obtained from its molten chloride by electrolysis, and that titanium is obtained from its chloride by reduction with magnesium. Why are these metals not obtained by the reduction of their oxides with carbon (coke), as are metals such as zinc and iron?

Vishal Sharma

Numerade Educator

Problem 55

The text notes that in small quantities, zinc is an essential element (though it is toxic in higher concentrations). Tin is considered to be a toxic metal. Can you think of reasons why, for food storage, tinplate instead of galvanized iron is used in cans?

Vishal Sharma

Numerade Educator

Problem 56

In an atmosphere polluted with industrial smog, $\mathrm{Cu}$ corrodes to a basic sulfate, $\mathrm{Cu}_{2}(\mathrm{OH})_{2} \mathrm{SO}_{4} .$ Propose a series of chemical reactions to describe this corrosion.

Vishal Sharma

Numerade Educator

Problem 57

What formulas would you expect for the metal carbonyls of (a) molybdenum, (b) osmium; (c) rhenium? Note that the simple carbonyls shown in Figure $23-15$ have one metal atom per molecule. Some metal carbonyls are binuclear; that is, they have two metal atoms bonded together in the carbonyl structure. Also, (d) explain why iron and nickel carbonyls are liquids at room temperature, whereas that of cobalt is a solid, and (e) describe the probable nature of the bonding in the compound $\mathrm{Na}\left[\mathrm{V}(\mathrm{CO})_{6}\right]$.

Vishal Sharma

Numerade Educator

Problem 58

For the straight-line graphs in Figure $23-8,$ explain why (a) breaks occur at the melting points and boiling points of the metals; (b) the slopes of the lines become more positive at these breaks; (c) the break at the boiling point is sharper than at the melting point.

Lottie Adams

Numerade Educator

Problem 59

Attempts to make $\mathrm{CuI}_{2}$ by the reaction of $\mathrm{Cu}^{2+}(\mathrm{aq})$ and $\mathrm{I}^{-}(\text {aq })$ produce $\mathrm{CuI}(\mathrm{s})$ and $\mathrm{I}_{3}^{-}(\mathrm{aq})$ instead. Without performing detailed calculations, show why this reaction should occur.
$$2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq}) \longrightarrow 2 \mathrm{CuI}(\mathrm{s})+\mathrm{I}_{3}^{-}(\mathrm{aq})$$

Vishal Sharma

Numerade Educator

Problem 60

Without performing detailed calculations, show that significant disproportionation of AuCl occurs if you attempt to make a saturated aqueous solution. Use data from Table 23.7 and $K_{\mathrm{sp}}(\mathrm{AuCl})=$ $2.0 \times 10^{-13}$.

Vishal Sharma

Numerade Educator

Problem 61

In acidic solution, silver(II) oxide first dissolves to produce $A g^{2+}(a q) .$ This is followed by the oxidation of $\mathrm{H}_{2} \mathrm{O}(\mathrm{l})$ to $\mathrm{O}_{2}(\mathrm{g})$ and the reduction of $\mathrm{Ag}^{2+}$ to $\mathrm{Ag}^{+}$
(a) Write equations for the dissolution and oxidationreduction reactions.
(b) Show that the oxidation-reduction reaction is indeed spontaneous.

Madi Sousa

Numerade Educator

Problem 62

Equation $(23.18),$ which represents the chromatedichromate equilibrium, is actually the sum of two equilibrium expressions. The first is an acid-base reaction, $\mathrm{H}^{+}+\mathrm{CrO}_{4}^{2-} \rightleftharpoons \mathrm{HCrO}_{4}^{-}$. The second
reaction involves elimination of a water molecule between two $\mathrm{HCrO}_{4}^{-}$ ions (a dehydration reaction), $2 \mathrm{HCrO}_{4}^{-} \rightleftharpoons \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{H}_{2} \mathrm{O} .$ If the ionization
constant, $K_{\mathrm{a}},$ for $\mathrm{HCrO}_{4}^{-}$ is $3.2 \times 10^{-7},$ what is the value of $K$ for the dehydration reaction?

Lottie Adams

Numerade Educator

Problem 63

Show that under the following conditions, $\mathrm{Ba}^{2+}(\mathrm{aq})$ can be separated from $\mathrm{Sr}^{2+}(\mathrm{aq})$ and $\mathrm{Ca}^{2+}($ aq) by precipitating $\mathrm{BaCrO}_{4}(\mathrm{s})$ with the other ions remaining in solution: $$\begin{aligned}
&\left[\mathrm{Ba}^{2+}\right]=\left[\mathrm{Sr}^{2+}\right]=\left[\mathrm{Ca}^{2+}\right]=0.10 \mathrm{M}\\
&\left[\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right]=\left[\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right]=1.0 \mathrm{M}\\
&\left[\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\right]=0.0010 \mathrm{M}\\
&\mathrm{K}_{\mathrm{sp}}\left(\mathrm{BaCrO}_{4}\right)=1.2 \times 10^{-10}\\
&K_{\mathrm{sp}}\left(\mathrm{SrCrO}_{4}\right)=2.2 \times 10^{-5}
\end{aligned}$$ Use data from this and previous chapters, as necessary.

Lottie Adams

Numerade Educator

Problem 64

A 0.589 g sample of pyrolusite ore (impure $\mathrm{MnO}_{2}$ ) is treated with $1.651 \mathrm{g}$ of oxalic acid $\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)$
in an acidic medium (reaction 1). Following this, the excess oxalic acid is titrated with $30.06 \mathrm{mL}$ of $0.1000 \mathrm{M}$ $\mathrm{KMnO}_{4}$ (reaction 2). What is the mass percent of $\mathrm{MnO}_{2}$ in the pyrolusite? The following equations are neither complete nor balanced.
(1) $\quad \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{MnO}_{2}(\mathrm{s}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})$
(2) $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 65

Both $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$ and $\mathrm{MnO}_{4}^{-}(\mathrm{aq})$ can be used to
titrate $\mathrm{Fe}^{2+}(\mathrm{aq})$ to $\mathrm{Fe}^{3+}(\mathrm{aq}) .$ Suppose you have available as titrants two solutions: $0.1000 \mathrm{M} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$
and $0.1000 \mathrm{M} \mathrm{MnO}_{4}^{-}(\mathrm{aq})$.
(a) For which solution would the greater volume of titrant be required for the titration of a particular sample of $\mathrm{Fe}^{2+}(\text { aq }) ?$ Explain.
(b) How many $\mathrm{mL}$ of $0.1000 \mathrm{M} \mathrm{MnO}_{4}^{-}($ aq) would be required for a titration if the same titration requires $24.50 \mathrm{mL}$ of $0.1000 \mathrm{M} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq}) ?$

Lottie Adams

Numerade Educator

Problem 66

The only important compounds of $\mathrm{Ag}(\mathrm{II})$ are $\mathrm{AgF}_{2}$ and AgO. Why would you expect these two compounds to be stable, but not other silver(II) compounds such as $\mathrm{AgCl}_{2}, \mathrm{AgBr}_{2},$ and $\mathrm{AgS} ?$

Emily Marty

Numerade Educator

Problem 67

What products are obtained when $\mathrm{Mg}^{2+}(\mathrm{aq})$ and $\mathrm{Cr}^{3+}(\mathrm{aq})$ are each treated with a limited amount of NaOH(aq)? With an excess of $\mathrm{NaOH}($ aq)? Why are the results different in these two cases?A certain steel is to be analyzed for $\mathrm{Cr}$ and $\mathrm{Mn}$. By suitable treatment, the Cr in the steel is oxidized to $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$ and the $\mathrm{Mn}$ to $\mathrm{MnO}_{4}(\mathrm{aq}) . \mathrm{A} 10.000 \mathrm{g}$
sample of steel is used to produce $250.0 \mathrm{mL}$ of a solution containing $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$ and $\mathrm{MnO}_{4}^{-}(\mathrm{aq}) . \mathrm{A} 10.00 \mathrm{mL}$
portion of this solution is added to $\mathrm{BaCl}_{2}(\mathrm{aq}),$ and by proper adjustment of the $\mathrm{pH}$, the chromium is completely precipitated as $\mathrm{BaCrO}_{4}(\mathrm{s}) ; 0.549 \mathrm{g}$ is obtained. A second $10.00 \mathrm{mL}$ portion of the solution requires exactly $15.95 \mathrm{mL}$ of $0.0750 \mathrm{M} \mathrm{Fe}^{2+}(\mathrm{aq})$ for its titration in acidic solution. Calculate the $\%$ Cr and \% $\mathrm{Mn}$ in the steel sample. [Hint: In the titration $\mathrm{MnO}_{4}^{-}(\mathrm{aq})$ is reduced to $\mathrm{Mn}^{2+}(\mathrm{aq})$ and $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})$ is reduced to
$\left.\mathrm{Cr}^{3+}(\mathrm{aq}) ; \text { the } \mathrm{Fe}^{2+}(\mathrm{aq}) \text { is oxidized to } \mathrm{Fe}^{3+}(\mathrm{aq}) \cdot\right]$

Lottie Adams

Numerade Educator

Problem 68

Nickel can be determined as nickel dimethylglyoximate, a brilliant scarlet precipitate that has the composition $20.31 \% \mathrm{Ni}, 33.26 \% \mathrm{C}, 4.88 \% \mathrm{H}, 22.15 \% \mathrm{O},$ and
$19.39 \%$ N. $\mathrm{A} 15.020 \mathrm{g}$ steel sample is dissolved in concentrated HCl(aq). The solution obtained is suitably treated to remove interfering ions, to establish the proper $\mathrm{pH},$ and to obtain a final solution volume of $250.0 \mathrm{mL} .$ A $10.00 \mathrm{mL}$ sample of this solution is then treated with dimethylglyoxime. The mass of purified, dry nickel dimethylglyoximate obtained is $0.104 \mathrm{g}$
(a) What is the empirical formula of nickel dimethylglyoximate?
(b) What is the mass percent nickel in the steel sample?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 69

A solution is believed to contain one or more of the following ions: $\mathrm{Cr}^{3+}, \mathrm{Zn}^{2+}, \mathrm{Fe}^{3+}, \mathrm{Ni}^{2+} .$ When the solution
is treated with excess $\mathrm{NaOH}(\mathrm{aq}),$ a precipitate forms. The solution in contact with the precipitate is colorless. The precipitate is dissolved in $\mathrm{HCl}(\mathrm{aq}),$ and the resulting solution is treated with $\mathrm{NH}_{3}(\text { aq })$. No precipitation occurs. Based solely on these observations, what conclusions can you draw about the ions present in the original solution? That is, which ion(s) are likely present, which are most likely not present, and about which can we not be certain? [Hint: Refer to Appendix D for solubility product and complex-ion formation data.

Kevin Chimex

Numerade Educator

Problem 70

Nearly all mercury(II) compounds exhibit covalent bonding. Mercury(II) chloride is a covalent molecule that dissolves in warm water. The stability of this compound is exploited in the determination of the levels of chloride ion in blood serum. Typical human blood serum levels range from 90 to $115 \mathrm{mmol} \mathrm{L}^{-1}$ The chloride concentration is determined by titration with $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2} .$ The indicator used in the titration is diphenylcarbazone, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{N}=\mathrm{NCONHNHC}_{6} \mathrm{H}_{5}$
which complexes with the mercury(II) ion after all the chloride has reacted with the mercury(II). Free diphenylcarbazone is pink in solution, and when it is complexed with mercury(II), it is blue. Thus, the diphenylcarbazone acts as an indicator, changing from pink to blue when the first excess of mercury(II) appears. In an experiment, $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}($ aq) solution is standardized by titrating $2.00 \mathrm{mL}$ of $0.0108 \mathrm{M} \mathrm{NaCl}$ solution. It takes $1.12 \mathrm{mL}$ of $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$ to reach the diphenylcarbazone end point. A 0.500 mL serum sample is treated with 3.50 mL water, 0.50 mL of 10\% sodium tungstate solution, and $0.50 \mathrm{mL}$ of $0.33 \mathrm{M}$ $\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})$ to precipitate proteins. After the proteins are precipitated, the sample is filtered and a $2.00 \mathrm{mL}$ aliquot of the filtrate is titrated with $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}$ solution, requiring $1.23 \mathrm{mL}$. Calculate the concentration of Cl^- Express your answer in mmol L $^{-1}$. Does this concentration fall in the normal range?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 71

Covalent bonding is involved in many transition metal compounds. Draw Lewis structures, showing any nonzero formal charges, for the following molecules or ions: (a) $\mathrm{Hg}_{2}^{2+} ;$ (b) $\mathrm{Mn}_{2} \mathrm{O}_{7} ;$ (c) $\mathrm{OsO}_{4}$. [Hint: In (b), there is one $\mathrm{Mn}-\mathrm{O}-\text { Mn linkage in the molecule. }\rfloor$

Lottie Adams

Numerade Educator

Problem 72

For a coordination number of four, the radius of $\mathrm{Mn}^{7+}$ has been estimated to be $39 \mathrm{pm}$. Estimate the charge density for the $\mathrm{Mn}^{7+}$ ion. Express your answer in $\mathrm{Cmm}^{-3} .$ How does this compare with the charge density of $\mathrm{Be}^{2+}$ given in Table $21.4 ?$ Would you expect the bonding in $\mathrm{Mn}_{2} \mathrm{O}_{7}$ to be primarily ionic or primarily covalent? Explain.

Lottie Adams

Numerade Educator

Problem 73

Nitinol is a nickel-titanium alloy known as memory metal. The name nitinol is derived from the symbols for nickel (Ni), titanium (Ti), and the acronym for the Naval Ordinance Laboratory (NOL), where it was discovered. If an object made out of nitinol is heated to about $500^{\circ} \mathrm{C}$ for about an hour and then allowed to cool, the original shape of the object is "remembered," even if the object is deformed into a different shape. The original shape can be restored by heating the metal. Because of this property, nitinol has found many uses, especially in medicine and orthodontics (for braces). Nitinol exists in a number of different solid phases. In the so-called austerite phase, the metal is relatively soft and elastic. The crystal structure for the austerite phase can be described as a simple cubic lattice of Ti atoms with Ni atoms occupying cubic holes in the lattice of Ti atoms. What is the empirical formula of nitinol and what is the percent by mass of titanium in the alloy?

Vishal Sharma

Numerade Educator

Problem 74

As a continuation of Problem 94 of Chapter 19 and the discussion on page $1040,$ consider the three graphs of $\Delta G^{\circ}$ as a function of temperature shown in the following figure.
(a) Explain the shapes of the three graphs. Specifically, why is one line essentially parallel to the temperature axis, why does one have a positive slope, and why does one have a negative slope?
(b) Table 23.2 lists as an additional blast furnace reaction, $\mathrm{C}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CO}(\mathrm{g}) .$ Determine
how $\Delta G^{\circ}$ for this reaction is related to the three reactions shown in the figure, and plot $\Delta G^{\circ}$ for this reaction as a function of temperature. If an equilibrium is established in this reaction at $1000^{\circ} \mathrm{C}$ and the partial pressure of $\mathrm{CO}_{2}(\mathrm{g})$ is 0.25 atm, what should be the equilibrium partial pressure of $\mathrm{CO}(g) ?$

Caroline Basil

Numerade Educator

Problem 75

Several transition metal ions are found in cation group 3 of the qualitative analysis scheme outlined in Figure $18-7 .$ At one point in the separation and testing of this group, a solution containing $\mathrm{Fe}^{3+}, \mathrm{Co}^{2+}, \mathrm{Ni}^{2+}$ $\mathrm{Al}^{3+}, \mathrm{Cr}^{3+},$ and $\mathrm{Zn}^{2+}$ is treated with an excess of $\mathrm{NaOH}(\mathrm{aq}),$ together with $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})$
(1) The excess $\mathrm{NaOH}($ aq) causes three of the cations to precipitate as hydroxides and three to form hydroxo complex ions.
(2) In the presence of $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}),$ the cation in one of the insoluble hydroxides is oxidized from the +2 to the +3 oxidation state, and one of the hydroxo complex ions is also oxidized.
(3) The three insoluble hydroxides are found as a dark precipitate.
(4) The solution above the precipitate has a yellow color.
(5) The dark precipitate from (3) reacts with HCl(aq), and all the cations return to solution; one of the cations is reduced from the +3 to the +2 oxidation state.
(6) The solution from (5) is treated with $6 \mathrm{MNH}_{3}(\mathrm{aq})$ and a precipitate containing one of the cations forms.
(a) Write equations for the reactions referred to in item (1).
(b) Write an equation for the most likely reaction in which a hydroxide precipitate is oxidized in item (2).
(c) What is the ion responsible for the yellow color of the solution in item (4)? Write an equation for its formation.
(d) Write equations for the dissolution of the precipitate and the reduction of the cation in item (5).
(e) Write an equation for the precipitate formation in item (6). [Hint: You may need solubility product and complex-ion formation data from Appendix D, together with descriptive information from this chapter and from elsewhere in the text.]

Nadia Lara

Numerade Educator

Problem 76

In your own words, define the following terms:
(a) domain; (b) flotation; (c) leaching; (d) amalgam.

Vishal Sharma

Numerade Educator

Problem 77

Briefly describe each of the following ideas, phenomena, or methods: (a) lanthanide contraction; (b) zone refining; (c) basic oxygen process; (d) slag formation.

Vishal Sharma

Numerade Educator

Problem 78

Explain the important distinctions between each pair of terms: (a) ferromagnetism and paramagnetism;
(b) roasting and reduction; (c) hydrometallurgy and pyrometallurgy; (d) chromate and dichromate.

Vishal Sharma

Numerade Educator

Problem 79

Describe the chemical composition of the material called (a) pig iron; (b) ferromanganese alloy;
(c) chromite ore; (d) brass; (e) aqua regia; (f) blister copper; (g) stainless steel.

Vishal Sharma

Numerade Educator

Problem 80

Three properties expected for transition elements are
(a) low melting points; (b) high ionization energies;
(c) colored ions in solution; (d) positive standard electrode (reduction) potentials; (e) diamagnetism;
(f) complex ion formation; (g) catalytic activity.

Vishal Sharma

Numerade Educator

Problem 81

The only diamagnetic ion of the following group is
(a) $\mathrm{Cr}^{2+} ;$ (b) $\mathrm{Zn}^{2+} ;$ (c) $\mathrm{Fe}^{3+} ;$ (d) $\mathrm{Ag}^{2+} ;$ (e) $\mathrm{Ti}^{3+}$.

Vishal Sharma

Numerade Educator

Problem 82

All of the following elements have an ion displaying the +6 oxidation state except (a) Mo; (b) Cr; (c) Mn;
(d) $\mathrm{V} ;$ (e) S.

Vishal Sharma

Numerade Educator

Problem 83

The best oxidizing agent of the following group of ions is (a) $\mathrm{Ag}^{+}(\mathrm{aq}) ;$ (b) $\mathrm{Cl}^{-}(\mathrm{aq}) ;$ (c) $\mathrm{H}^{+}(\mathrm{aq})$ (d) $\mathrm{Na}^{+}(\mathrm{aq}) ;$ (e) $\mathrm{OH}^{-}(\mathrm{aq})$

Vishal Sharma

Numerade Educator

Problem 84

To separate $\mathrm{Fe}^{3+}$ and $\mathrm{Ni}^{2+}$ from an aqueous solution containing both ions, with one cation forming a precipitate and the other remaining in solution, add to the solution (a) $\mathrm{NaOH}(\mathrm{aq}) ;$
(b) $\mathrm{H}_{2} \mathrm{S}(\mathrm{g})$
(c) $\mathrm{HCl}(\mathrm{aq}) ;(\mathrm{d}) \mathrm{NH}_{3}(\mathrm{aq})$

Vishal Sharma

Numerade Educator

Problem 85

Of the following, the two solids that will liberate $\mathrm{Cl}_{2}(\mathrm{g})$ when heated with $\mathrm{HCl}(\mathrm{aq})$ are $(\mathrm{a}) \mathrm{NaCl}(\mathrm{s})$
(b) $\mathrm{ZnCl}_{2}(\mathrm{s}) ;(\mathrm{c}) \mathrm{MnO}_{2}(\mathrm{s}) ;(\mathrm{d}) \mathrm{CuO}(\mathrm{s}) ;(\mathrm{e}) \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{s})$
(f) $\mathrm{NaOH}(\mathrm{s})$

Vishal Sharma

Numerade Educator

Problem 86

Provide the missing name or formula for the following:

Lottie Adams

Numerade Educator

Problem 87

Balance the following oxidation-reduction equations.
$$\text { (a) } \mathrm{Fe}_{2} \mathrm{S}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow \mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})+\mathrm{S}(\mathrm{s})$$
$$\begin{aligned}
&\text { (b) } \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{S}_{2} \mathrm{O}_{8}^{2-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O} \longrightarrow\\
&&\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{SO}_{4}^{2-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq})
\end{aligned}$$
$$\begin{aligned}
&\text { (c) } \mathrm{Ag}(\mathrm{s})+\mathrm{CN}^{-}(\mathrm{aq})+\mathrm{O}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O} \longrightarrow\\
&&\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]^{-}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})
\end{aligned}$$

Lottie Adams

Numerade Educator

Problem 88

Explain why $\mathrm{Zn}, \mathrm{Cd},$ and $\mathrm{Hg}$ resemble the group 2 metals in some of their properties.

Vishal Sharma

Numerade Educator

Problem 89

Explain why gold dissolves in aqua regia but not in $\mathrm{HNO}_{3}(\mathrm{aq})$.

Vishal Sharma

Numerade Educator

Problem 90

Explain why $1.0 \mathrm{M} \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}(\mathrm{aq})$ is acidic.

Vishal Sharma

Numerade Educator