Problem 96 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I List II 1\. \(\mathrm{Cu}^{2+}\) (i) colourless 2\. \(\mathrm{Ni}^{2+}\) (ii) green 3\. \(\mathrm{Fe}^{3+}\) (iii) yellow 4\. \(\mathrm{Ti}^{3+}\) (iv) blue (v) purple The correct matching is: \(1 \quad 2 \quad 3\) 4 (a) (i) (ii) (iii) (v) (b) (i) (iii) (ii) (iv) (c) (ii) (i) (iii) (v) (d) (iv) (ii) (iii) (v)

Step-by-Step Solution

Answer

The correct matching is option (d).

Step 1: Understand the Ion Colors

Review the typical color of each ion's solution. - \( \mathrm{Cu}^{2+} \) is commonly blue in solution.- \( \mathrm{Ni}^{2+} \) is often green in solution.- \( \mathrm{Fe}^{3+} \) usually appears yellow or brownish-yellow in solution.- \( \mathrm{Ti}^{3+} \) typically has a purple tint.

Step 2: Match the Options

Using the colors identified in Step 1, match each ion to its corresponding color in List II:- \( \mathrm{Cu}^{2+} \) matches to (iv) blue.- \( \mathrm{Ni}^{2+} \) matches to (ii) green.- \( \mathrm{Fe}^{3+} \) matches to (iii) yellow.- \( \mathrm{Ti}^{3+} \) matches to (v) purple.

Step 3: Identify the Correct Pattern

Write down the pattern according to the matches: - 1 matches (iv) - 2 matches (ii) - 3 matches (iii) - 4 matches (v) This sequence aligns with option (d): 1 - (iv), 2 - (ii), 3 - (iii), 4 - (v).

Key Concepts

Color of Ions

When you dissolve transition metal ions in water, they often form colorful solutions. This is because of the unique properties of these metal ions. The specific colors we see are due to the way the ions interact with light.

• Different transition metal ions absorb light at specific wavelengths.
• This absorption happens when electrons transition between different energy levels in the ions.

For example,

• \(\mathrm{Cu}^{2+}\) ions tend to absorb yellow and red wavelengths, so the light that is reflected appears blue.
• \(\mathrm{Ni}^{2+}\) ions absorb wavelengths more towards the red end, resulting in a green appearance.
• \(\mathrm{Fe}^{3+}\) ions absorb some faint ultraviolet and visible light, showing a yellowish tint.
• \(\mathrm{Ti}^{3+}\) absorbs in a way that results in a purple hue.

Each type of metal ion provides a unique color specific to its electron arrangement and interaction with light.

Coordination Chemistry

Coordination chemistry is the study of complex compounds that contain a central metal atom bonded to surrounding molecules or ions. These molecules or ions are known as ligands. In transition metals, coordination chemistry plays a crucial role.

• Transition metals have unique ability to form complex structures with ligands.
• Ligands in a coordination compound can greatly influence the overall properties, including color.

Coordination compounds are essential because they often enhance the properties of the transition metal. For instance:

• The color intensity can change with different ligands bonding to the metal ion.
• The shape and stability of coordination compounds are dictated by the number and type of ligands attached.

Understanding coordination complexes is crucial for explaining the colors we observe in solutions containing metal ions.

Electronic Configurations of Ions

Electronic configurations refer to the arrangement of electrons around a nucleus. For ions, electronic configurations differ slightly because of the gain or loss of electrons.

• Transition metal ions typically lose electrons from their s and sometimes d subshells when they form cations.
• Losing electrons affects their electronic configuration, which influences their chemical and physical properties.

For transition metals:

• Normal electronic arrangements can be altered when ions are present, as the s orbital electrons are usually lost first.
• For example, \(\mathrm{Cu}^{2+}\) has an electronic configuration of \([\mathrm{Ar}] 3d^9\), since two 4s electrons are lost when copper forms a +2 ion.
• This change in electron availability is responsible for their ability to absorb light at certain wavelengths, leading to the observed color.

Understanding these configurations is fundamental to predicting the behavior and color of transition metal ions in solution.