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Chapter 4: Problem 39

In which of the following pairs are both the ions coloured in aqueous solution? (a) \(\mathrm{Sc}^{3+}, \mathrm{Co}^{2+}\) (b) \(\mathrm{Ni}^{2+}, \mathrm{Cu}^{+}\) (c) \(\mathrm{Ni}^{2+}, \mathrm{Ti}^{\mathrm{i}}\) (d) \(\mathrm{Sc}^{3+}, \mathrm{Ti}^{3+}\) (At. no. \(\mathrm{Sc}=21, \mathrm{Ti}=22, \mathrm{Ni}=28, \mathrm{Cu}=29, \mathrm{Co}=27\) )

Short Answer

Expert verified
None of the given pairs have both ions colored.

Step by step solution

01

Understand the Coloration of Ions

In aqueous solutions, ions may appear colored because of the presence of unpaired electrons, which allows electronic transitions that absorb light in the visible spectrum. Transition metal ions are often colored due to these electronic transitions.
02

Analyze the Electronic Configuration for Coloration

To determine whether both ions in a pair are colored, we need to consider their electronic configurations. If an ion has unpaired electrons in the d-orbital, the ion will likely be colored. Let's analyze the given pairs.
03

Evaluate Pair (a): Sc^{3+} and Co^{2+}

The electronic configuration of \( \mathrm{Sc}^{3+} \) is \([\mathrm{Ar}]\) (no electrons in d-orbital), and has no unpaired electrons, making it colorless. \( \mathrm{Co}^{2+} \) has the electronic configuration \([\mathrm{Ar}]\, 3d^7\), which has unpaired electrons, so it is colored.
04

Evaluate Pair (b): Ni^{2+} and Cu^{+}

\( \mathrm{Ni}^{2+} \) has the electronic configuration \([\mathrm{Ar}]\, 3d^8\); it has unpaired electrons, making it colored. \( \mathrm{Cu}^{+} \) has the electronic configuration \([\mathrm{Ar}]\, 3d^{10}\), which is fully filled with no unpaired electrons, making it colorless.
05

Evaluate Pair (c): Ni^{2+} and Ti^{4+}

\( \mathrm{Ni}^{2+} \) is colored as previously determined. For \( \mathrm{Ti}^{4+} \), the electronic configuration is \([\mathrm{Ar}]\) (no electrons in d-orbital), which is colorless due to having no unpaired electrons.
06

Evaluate Pair (d): Sc^{3+} and Ti^{3+}

\( \mathrm{Sc}^{3+} \) is colorless as previously determined. \( \mathrm{Ti}^{3+} \) has the electronic configuration \([\mathrm{Ar}]\, 3d^1\), which has unpaired electrons, so it is colored.
07

Conclusion

After evaluating the four pairs, only \( \mathrm{Ni}^{2+} \) contains ions that show coloration in an aqueous solution, but paired only with another colored ion would be relevant here. None of the options have both ions colored.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Transition Metal Ions
Transition metal ions are unique in their ability to form colored compounds. This happens because they have partially filled d-orbitals. A transition metal is defined as an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell. These metals are characterized by a variable oxidation state. They are pivotal in forming a variety of colorful compounds.
Some key traits include:
  • The presence of d-orbitals allows these metals to exhibit different oxidation states.
  • They often form colored ions due to d-d electron transitions.
  • Common examples include Iron (Fe), Copper (Cu), Nickel (Ni), and Cobalt (Co).
Unpaired Electrons
Unpaired electrons play a crucial role in determining the color of a metal ion. An unpaired electron is a single electron that doesn't have a partner with an opposite spin in the same orbital. In transition metals, these unpaired electrons typically reside in d-orbitals.
Here are some main points about unpaired electrons:
  • The presence of unpaired electrons allows electronic transitions to occur, which are required for color.
  • Transition metal ions with unpaired d-electrons can absorb specific wavelengths of light, resulting in colorful solutions.
  • An ion with fully filled or empty d-orbitals generally does not show color in aqueous solutions.
Electronic Configuration
Understanding the electronic configuration of ions helps anticipate their properties, including coloration. This refers to the arrangement of electrons in an atom across different orbitals. The electronic configuration reveals how electrons are distributed among the atom's orbitals.
Key insights into electronic configuration include:
  • The electronic configuration defines the number of unpaired electrons, which is crucial for color production.
  • Transition metal ions often have electronic configurations ending with d-orbitals, like \([ ext{Ar}] 3d^8\) for \( ext{Ni}^{2+}\).
  • Knowing the electronic configuration helps predict the magnetic and optical properties of the ion.
Coloration in Aqueous Solutions
The colorful nature of some transition metal ions when dissolved in water is due to their electronic structure. They absorb specific wavelengths of light, and the light that is not absorbed is transmitted or reflected, which makes the solution appear colorful. This phenomenon is rooted deeply in their electronic transitions.
More about coloration in aqueous solutions:
  • Only ions with unpaired d-electrons show coloration. For example, \( ext{Co}^{2+}\) in water appears pink due to the absorption and transition within its unpaired electrons.
  • A complex formation with water molecules often affects the color exhibited by ions.
  • Factors such as the oxidation state of the metal and the nature of ligands in the solution contribute to observed colors.

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Most popular questions from this chapter

If a source of power \(4 \mathrm{Kw}\) produces \(10^{20}\) photon Per second, the radiation belongs to a part of the spectrum called (a) \(\gamma\)-Rays (b) U.V Rays (c) Microwaves (d) X-Rays

Among the following series of transition metal ions, the one where all metal ion have \(3 \mathrm{~d}^{2}\) electronic configuration is (a) \(\mathrm{Ti}^{3+}, \mathrm{V}^{2+}, \mathrm{Cr}^{3+}, \mathrm{Mn}^{4+}\) (b) \(\mathrm{Ti}^{+}, \mathrm{V}^{4+}, \mathrm{Cr}^{6+}, \mathrm{Mn}^{7+}\) (c) \(\mathrm{Ti}^{4+}, \mathrm{V}^{3+}, \mathrm{Cr}^{2+}, \mathrm{Mn}^{3+}\) (d) \(\mathrm{Ti}^{2+}, \mathrm{V}^{3+}, \mathrm{Cr}^{4+}, \mathrm{Mn}^{5+}\) (At. wt \(\mathrm{Ti}=22, \mathrm{~V}=23, \mathrm{Cr}=24, \mathrm{Mn}=25)\)

How many \(\mathrm{e}^{-}\)are present in p-sub-orbits in \(\mathrm{Zn}\)-atom? (a) 2 (b) 6 (c) 12 (d) 18

Pick out the wrong statements. (a) \(\mathrm{Fe}^{3+}\) ion is more stable than \(\mathrm{Fe}^{2+}\) ion in the gaseous state. (b) For an electron in a \(4 \mathrm{p}\)-orbital, the quantum numbers are \(\mathrm{n}=4, l=1, \mathrm{~m}=2, \mathrm{~s}=+1 / 2\) (c) Angular momentum of 3 s electron is one. (d) \((\mathrm{n}+I)\) rule is followed for determining the orbital of the lowest energy state.

Which of the following statement is/ are correct? (a) The number of unpaired electrons in both \(\mathrm{Fe}^{2+}\) and \(\mathrm{Mn}^{2+}\) are five. (b) In silver atom, 23 electrons have a spin of one type and 24 of the opposite (atomic number of \(\mathrm{Ag}=\) 47).
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