Chapter 23

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

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

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.

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.

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?

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?

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

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?

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

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) \(\mathrm{MnO}_{2}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\)

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 \(\mathrm{HCl}(\mathrm{aq})\).

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 \(\mathrm{SO}_{2}(\mathrm{g})\).

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.

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 \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})\)

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) \(\operatorname{Cr} \mathrm{Cl}_{3}\left(\text { aq) } \text { from }\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{s})\right.\)

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.

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 \(2 \mathrm{Ca}(\mathrm{s})+\) \(\mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CaO}(\mathrm{s})\).

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.

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

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

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 \(\mathrm{SO}_{2}(\mathrm{g})\)

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

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.

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?

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?

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 \(\mathrm{Ni}(\mathrm{OH})_{2}\)

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.

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.

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.

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 \(\mathrm{O}_{2}(\mathrm{g}) ?\)

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.

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.

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?

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?

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?

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.

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. $$2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq}) \longrightarrow 2 \mathrm{CuI}(\mathrm{s})+\mathrm{I}_{3}^{-}(\mathrm{aq})$$

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 \(K_{\mathrm{sp}}(\mathrm{AuCl})=\) \(2.0 \times 10^{-13}\).

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.

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?

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.

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) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})\)

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 \(0.1000 \mathrm{M} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq}) ?\)

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 \(\mathrm{AgS} ?\)

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 \(\left.\mathrm{Cr}^{3+}(\mathrm{aq}) ; \text { the } \mathrm{Fe}^{2+}(\mathrm{aq}) \text { is oxidized to } \mathrm{Fe}^{3+}(\mathrm{aq}) \cdot\right]\)

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?

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.

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?

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 \(\mathrm{Mn}-\mathrm{O}-\text { Mn linkage in the molecule. }\rfloor\)

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?