Chapter 20

Write the formula for (a) tetrachlorocthylenediaminecobaltate(III). (b) triaquatrifluorocobalt(III).

Write the name corresponding to cach formula. (a) \(\left[\mathrm{MnCl}_{4}\right]^{2-}\) (b) \(\mathrm{K}_{3}\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (c) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{CN})_{2}\right]\)

Write the name corresponding to each formula. (a) \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\) (b) \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\)

Sketch the geometry of (a) \(c i s-\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2} \mathrm{Br}_{4}\right]^{2-}\). (b) trans-[Ni(NH \(\left.\left._{3}\right)_{2}(\mathrm{en})_{2}\right]^{2+}\).

The acetylacetonate ion (acac) forms a complex with \(\mathrm{Co}^{3+}\). Sketch the geometry of \(\left[\mathrm{Co}(\mathrm{acac})_{3}\right]\)

Which of these octahedral coordination complexes can exhibit geometric isomerism? (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3} \mathrm{Cl}_{3}\right]\) (b) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\right]^{+}\)

Which of these octahedral coordination complexes can exhibit geometric isomerism? (a) \(\left[\mathrm{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2} \mathrm{Cl}_{2} \mathrm{Br}_{2}\right]\) (b) \(\left[\mathrm{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2} \mathrm{Cl}_{3} \mathrm{Br}\right]\)

Draw the possible geometric isomers, if any. (a) \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\right]^{+}\) (b) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{3}\right]^{-}\) (c) \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3} \mathrm{Cl}_{3}\right]\) (d) \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{NH}_{3}\right) \mathrm{Br}\right]^{2+}\)

Draw the possible geometric isomers, if any, of (a) \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right]\) (b) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{SCN}) \mathrm{Br}\right]\). (The \(\mathrm{S}\) in \(\mathrm{SCN}\) is bonded to \(\mathrm{Pt}^{2+}\).) (c) \(\left[\mathrm{Co}(\mathrm{en}) \mathrm{Cl}_{4}\right]^{-}\)

Draw the crystal-field splitting diagrams and put in the d electrons for these octahedral complexes. In those cases where they are possible, draw diagrams for both low-spin and high-spin cases. (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (b) \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (c) \(\left[\mathrm{FeF}_{6}\right]^{\frac{3}{3}-}\) (d) \(\left[\mathrm{Cr}(\mathrm{en})_{3}\right]^{3+}\)

\(\mathrm{Fe}^{3+}\) forms octahedral complexes with \(\mathrm{NCS}^{-}\) and with \(\mathrm{NO}_{2}^{-}\) ligands. One complex displays a greater paramagnetism than the other. (a) Write the formula for each of these complex ions. (b) Use the spectrochemical series to predict whether the complex ions are high-spin or low-spin. (c) Identify which complex ion is more paramagnetic. (d) Draw the crystal-field splitting diagram, including delectrons, for each complex ion.

Explain why \(\mathrm{Cr}^{2+}\) forms high-spin and low-spin octahedral complexes, but \(\mathrm{Cr}^{3+}\) does not.

How many unpaired electrons are in the high-spin and low-spin octahedral complexes of \(\mathrm{Cr}^{2+} ?\)

Use crystal-field theory to explain why some \(\mathrm{Co}^{3+}\) octahedral complexes are diamagnetic and others are paramagnetic.

Use crystal-field theory to explain why some octahedral \(\mathrm{Co}^{2+}\) complexes are more paramagnetic than others.

Use crystal-field theory to explain why \(\mathrm{Cu}^{2+}\) does not form high- spin and low-spin octahedral complexes.

An aqueous solution of \(\left[\mathrm{Rh}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}\) is yellow. Predict the approximate wavelength and predominant color of light absorbed by the complex.

An aqueous solution of \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) is purple. Predict the approximate wavelength and predominant color of light absorbed by the complex.

A solution of a complex ion absorbs visible light at a wavelength of \(540 \mathrm{nm} .\) (a) What is the color of the solution? (b) Calculate the energy of an absorbed photon in joules and in \(\mathrm{kJ} / \mathrm{mol}\).

Give the electron configuration of (a) \(\mathrm{Cr}^{2+}\). (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Co}^{2+}\). (d) \(\mathrm{Mn}^{4+}\).

Give the electron configuration of (a) \(\mathrm{Ti}^{3+}\). (b) \(\mathrm{V}^{2+}\) (c) \(\mathrm{Ni}^{3+}\). (d) \(\mathrm{Cu}^{+}\).

Assuming \(100 \%\) recovery of the metal, which would yield the greater mass of copper? (a) One kilogram of an ore containing 3.60 mass \(\%\) azurite, \(\mathrm{Cu}(\mathrm{OH})_{2} \cdot 2 \mathrm{CuCO}_{3}\) (b) One kilogram of an ore containing 4.95 mass \% chalcopyrite, \(\operatorname{CuFeS}_{2}\)

Calculate the mass of copper that is electroplated from a \(\mathrm{CuSO}_{4}\) solution using an electric current of \(2.50 \mathrm{~A}\) for \(5.00 \mathrm{~h}\). Assume \(100 \%\) efficiency.

Copper metal is obtained directly by roasting covellite, \(\mathrm{CuS}\) (a) Write a balanced equation for this process. (b) Assume that the roasting is \(90.0 \%\) efficient. Calculate how many tons of \(\mathrm{SO}_{2}\) are released into the air by roasting 500 . tons of covellite.

Determine the coordination number of the central metal ion in (a) \(\left[\mathrm{Ni}(\mathrm{en}) \mathrm{Cl}_{2}\right]\) (b) \(\left[\mathrm{Mo}(\mathrm{CO})_{4} \mathrm{Br}_{2}\right]\) (c) \(\left[\mathrm{Cd}(\mathrm{CN})_{4}\right]^{2-}\). (d) \(\left[\mathrm{Co}(\mathrm{CN})_{5}(\mathrm{OH})\right]^{3-} .\)

Determine the coordination number of the central metal ion in (a) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Br}_{2}\right]\). (b) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\). (c) \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right) \mathrm{Cl}_{5}\right]^{2-}\) (d) \(\left[\mathrm{Mn}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{4-}\)

Draw structures for as many octahedral complexes as you can for the formula \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2} \mathrm{Br}\).

Draw structures for all possible octahedral complexes of \(\mathrm{Co}^{3+}\) using only ethylenediamine and/or \(\mathrm{Cl}^{-}\) as ligands.

In your own words explain why (a) \(\mathrm{H}_{2} \mathrm{~N}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{NH}_{2}\) is a bidentate ligand. (b) \(\mathrm{AgCl}\) dissolves in \(\mathrm{NH}_{3-}\) (c) there are no geometric isomers of tetrahedral complexes.

Determine whether each statement is true or false. If it is false, correct the statement. (a) The coordination number of the \(\mathrm{Fe}^{3+}\) ion in \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right]^{+}\) is five. (b) \(\mathrm{Cu}^{+}\) has two unpaired electrons. (c) The net charge of a coordination complex of \(\mathrm{Cr}^{3+}\) with two \(\mathrm{NH}_{3},\) one \(\mathrm{en},\) and \(\mathrm{two} \mathrm{H}_{2} \mathrm{O}\) is \(2+\)

Determine whether each statement is true or false. If it is false, correct the statement. (a) In \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{4}\right]\), platinum has a \(4+\) charge and a coordination number of six. (b) In general, \(\mathrm{Cu}^{2+}\) is more stable than \(\mathrm{Cu}^{+}\) in aqueous solutions.

The metal ion in \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right]\) is surrounded by a square planar array of coordinating atoms. (a) Give the oxidation number of the central metal ion. (b) Draw the structural formula of this coordination compound.

Iron nails are put into \(\mathrm{Fe}^{2+}\) aqueous solutions to reduce any \(\mathrm{Fe}^{3+}\) that forms back to \(\mathrm{Fe}^{2+} .\) Write a balanced chemical equation for this preventative reaction.

Use VSEPR theory to predict the shape and bond angles around chromium in (a) chromate ions. (b) dichromate ions.

Two different isomers are known with the formula \(\left[\mathrm{Pt}(\mathrm{py})_{2} \mathrm{Cl}_{2}\right],\) where py represents pyridine, an uncharged monodentate ligand in which an \(\mathrm{N}\) atom bonds to the metal ion. There is, however, only one structure known for \(\left[\mathrm{Pt}(\mathrm{phen}) \mathrm{Cl}_{2}\right],\) where phen represents 1,10 -phenanthroline, an uncharged bidentate ligand (Question 104 ). Draw the structural formulas of all three molecules and explain why there are isomers in one case, but not the other.

An electrochemical cell is made by immersing a strip of chromium into a \(1.0-\mathrm{M}\) solution of \(\mathrm{Cr}^{3+}\) and a strip of gold into a \(1.0-\mathrm{M}\) solution of \(\mathrm{Au}^{3+} .\) The half-cells are connected by a salt bridge. A wire and light bulb complete the circuit. (a) Write the balanced chemical equation for the reaction that is product- favored. (b) Calculate the cell potential. (c) Draw a sketch of the cell and indicate the anode, cathode, and direction of electron flow.

To determine the percent iron in an ore, a \(1.500-\mathrm{g}\) sample of the ore containing \(\mathrm{Fe}^{2+}\) is titrated to the equivalence point with \(18.6 \mathrm{~mL}\) of \(0.05012-\mathrm{M} \mathrm{KMnO}_{4} .\) The products of the titration are \(\mathrm{Fe}^{3+}\) and \(\mathrm{Mn}^{2+}\). Calculate the weight percent of iron in the ore.

Consider the reaction $$ 2 \mathrm{Cu}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Cu}^{2+}(\mathrm{aq})+\mathrm{Cu}(\mathrm{s}) $$ for which \(E_{\mathrm{cell}}^{\mathrm{o}}=+0.37 \mathrm{~V}\). Use the Nernst equation to calculate (a) \(E\) when the \(\mathrm{Cu}^{2+}\) concentration is equal to the \(\mathrm{Cu}^{+}\) concentration \(=1 \times 10^{-4} \mathrm{M}\) (b) the concentration of \(\mathrm{Cu}^{+}\) when the \(\mathrm{Cu}^{2+}\) concentration = 1.0 \(\mathrm{M}\) and \(E=0.00 \mathrm{~V}\).

Consider the reaction $$ 2 \mathrm{Ag}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Ag}(\mathrm{s})+\mathrm{Ag}^{2+}(\mathrm{aq}) $$ for which \(E_{\text {cell }}^{\underline{\phantom{xxx}}}=-1.18 \mathrm{~V}\). Use the Nernst equation to calculate (a) \(E\) when the \(\mathrm{Ag}^{+}\) concentration \(=1 \times 10^{-4} \mathrm{M},\) which is five times the concentration of \(\mathrm{Ag}^{2+}\) (b) the concentration of \(\mathrm{Ag}^{2+}\) when the \(\mathrm{Ag}^{+}\) concentration $$ =1.0 \mathrm{M} \text { and } E=0.00 \mathrm{~V} \text { . } $$

If \(1.00 \mathrm{~mol}\) of each compound is dissolved in a separate sample of water sufficient to dissolve the compound, how many moles of ions are present in each solution? (a) \(\left[\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\right]\) (b) \(\mathrm{Na}\left[\mathrm{Cr}(\mathrm{en})_{2}\left(\mathrm{SO}_{4}\right)_{2}\right]\) (c) \(\mathrm{K}_{3}\left[\mathrm{Au}(\mathrm{CN})_{4}\right]\) (d) \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\)

In aqueous solution, \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}\) is yellow, but aqueous \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{2}\) is purple. Explain the difference in colors.

Early coordination chemists relied on close experimental observation to determine the formulas of coordination compounds. They found, for example, that aqueous \(\mathrm{BaCl}_{2}\) did not cause precipitation when added to a solution of a \(\mathrm{Co}^{3+}\) -containing coordination compound, but precipitation occurred when aqueous silver nitrate was added to a solution of the coordination compound. The coordination compound was known to contain one \(\mathrm{Co}^{3+}\) ion, one sulfate ion, one chloride ion, and four ammonia molecules. Write the structural formula of the coordination compound that is consistent with the experimental results.

The bidentate oxalate ion, \(\mathrm{C}_{2} \mathrm{O}_{4}^{2-},\) forms octahedral complexes with \(\mathrm{Fe}^{3+}\) and \(\mathrm{Ru}^{3+}\) ions. (a) Write the structural formula for each complex. (b) The ruthenium complex is low-spin; the iron complex is high-spin. Write the \(d\) -orbital splitting diagram for each metal ion. (c) Which complex has the higher \(\Delta_{\circ}\) ? Explain your answer.

Analysis of a coordination compound gives these results: \(22.0 \%\) Co, \(31.4 \% \mathrm{~N}, 6.78 \% \mathrm{H},\) and \(39.8 \% \mathrm{Cl} .\) One mole of the compound dissociates in water to form 4 mol ions. (a) Determine the formula of the compound. (b) Write the equation for its dissociation in water.

The glycinate ion (gly) is \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2}^{-}\). It can act as a ligand coordinating through the nitrogen and one of the oxygens. Using \(\mathrm{N}\) O to represent glycinate ion, draw structural formulas for four stereoisomers of [Co(gly)_3].

Five-coordinate coordination complexes are known, including \(\left[\mathrm{CuCl}_{5}\right]^{3-}\) and \(\left[\mathrm{Ni}(\mathrm{CN})_{5}\right]^{3-} .\) Write the structural formulas and identify a plausible geometry for these complexes.

Predict the number of unpaired electrons in a square planar transition metal ion with seven \(d\) electrons.

A coordination compound has the empirical formula \(\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{CN})_{2} .\) Its paramagnetism is the equivalent of 2.67 unpaired electrons per Fe ion. Explain how this is possible.

Two different compounds are known with the formula \(\mathrm{Pd}(\mathrm{py})_{2} \mathrm{Cl}_{2},\) but there is only one compound with the formula \(\mathrm{Zn}(\mathrm{py})_{2} \mathrm{Cl}_{2}\). The symbol py is for pyridine, a monodentate ligand. Explain the differences in the Pd and \(Z \mathrm{n}\) compounds.

An octahedral coordination complex ion is formed by the combination of an \(\mathrm{Fe}^{3+}\) ion and det ligands (det is \(\left.\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right) .\) Write a structural formula for the complex ion.