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Chapter 24: Problem 56

Explain why aqueous solutions of \(\left[\operatorname{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{3}\) and \(\left.\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Cl}_{2}\) are colorless, but an aqueous solution of \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{3}\) is not.

Short Answer

Expert verified
Scandium and Zinc complexes are colorless because there are no unpaired d electrons in their complexes, so 'd-d' transitions are not possible. However, the Iron complex has unpaired d electrons, so these transitions can occur, and the complex can absorb wavelengths within the visible light range, which gives it a color.

Step by step solution

01

Understanding Scandium Complex

For the Scandium complex, Sc\[ \left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\] Cl_{3}, consider the atomic number of scandium, which is 21. Its electron configuration ends in 3d1 4s2. When the Scandium ion is formed (Sc^3+), the 3d and 4s electrons are lost, leaving no unpaired d electrons. Therefore, there cannot be any 'd-d' transition. As a result, the Scandium complex is colorless.
02

Understanding Zinc Complex

For the Zinc complex, Zn\[ \left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\] Cl_{2}, the atomic number of zinc is 30, and its electron configuration ends in 3d10 4s2. When the Zinc ion is formed (Zn^2+), the 4s electrons are lost, with the 3d10 orbital completely filled. Again, as there are no unpaired d electrons, there can't be any 'd-d' transitions. Therefore, the Zinc complex is also colorless.
03

Understanding Iron Complex

In the case of the Iron complex, Fe\[ \left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\] Cl_{3}, Iron has an atomic number of 26, with electron configuration ending in 3d6 4s2. When the Iron ion (Fe^3+) is formed, it loses the 3d and 4s electrons, leaving five in the 3d orbital. This means there are unpaired electrons, and as a result, 'd-d' transitions are possible. Therefore, the Iron complex can absorb certain wavelengths within the visible light range, giving it color.

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Most popular questions from this chapter

From each of the following names, you should be able to deduce the formula of the complex ion or coordination compound intended. Yet, these are not the best systematic names that can be written. Replace each name with one that is more acceptable: (a) cupric tetraammine ion; (b) dichlorotetraammine cobaltic chloride; (c) platinic(IV) hexachloride ion; (d) disodium copper tetrachloride; (e) dipotassium antimony(III) pentachloride.

Estimate the total \(\left[\mathrm{Cl}^{-}\right]\) required in a solution that is initially \(0.10 \mathrm{M} \mathrm{CuSO}_{4}\) to produce a visible yellow color. \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right]^{2+}+4 \mathrm{Cl}^{-} \rightleftharpoons\left[\mathrm{CuCl}_{4}\right]^{2-}+4 \mathrm{H}_{2} \mathrm{O}\) \(K_{f}=4.2 \times 10^{5}\) Assume that \(99 \%\) conversion of \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right]^{2+}\) to \(\left[\mathrm{CuCl}_{4}\right]^{2-}\) is sufficient for this to happen, and ignore the presence of any mixed aqua- chloro complex ions.

Explain the following observations in terms of complex-ion formation. (a) \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) is soluble in \(\mathrm{NaOH}(\mathrm{aq})\) but insoluble in \(\mathrm{NH}_{3}(\mathrm{aq})\) (b) \(\mathrm{ZnCO}_{3}(\mathrm{s})\) is soluble in \(\mathrm{NH}_{3}(\mathrm{aq}),\) but \(\mathrm{ZnS}(\mathrm{s})\) is not. (c) The molar solubility of AgCl in pure water is about \(1 \times 10^{-5} \mathrm{M} ;\) in \(0.04 \mathrm{M} \mathrm{NaCl}(\mathrm{aq}),\) it is about \(2 \times 10^{-6}; \mathrm{M}\) but in \(1 \mathrm{M} \mathrm{NaCl}(\mathrm{aq}),\) it is about \(8 \times 10^{-5} \mathrm{M}\).

Supply acceptable names for the following. (a) \(\left[\mathrm{Co}(\mathrm{OH})\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{NH}_{3}\right)\right]^{2+}\) (b) \(\left[\mathrm{Co}(\mathrm{ONO})_{3}\left(\mathrm{NH}_{3}\right)_{3}\right]\) (c) \(\left[\operatorname{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right]\left[\mathrm{PtCl}_{6}\right]\) (d) \(\left[\mathrm{Fe}(\mathrm{ox})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{-}\) (e) \(\mathrm{Ag}_{2}\left[\mathrm{HgI}_{4}\right]\)

Write equations to represent the following observations. (a) A quantity of \(\mathrm{CuCl}_{2}(\mathrm{s})\) is dissolved in concentrated HCl(aq) and produces a yellow solution. The solution is diluted to twice its volume with water and assumes a green color. On dilution to ten times its original volume, the solution becomes pale blue. (b) When chromium metal is dissolved in \(\mathrm{HCl}(\mathrm{aq}), \mathrm{a}\) blue solution is produced that quickly turns green. Later the green solution becomes blue-green and then violet.
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