Problem 121 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following \begin{tabular}{ll} \hline Column-I & Column-II \\ \hline (a) \(\mathrm{Ce}^{4+}\) & (p) Oxidizing agent in volu- \\ metric analysis \\ (b) \(\mathrm{Nd}^{3+}\) & (q) Misch metal \\ (c) \(\mathrm{La}^{3+}\) & (r) Colourless salts \\ \(\begin{array}{ll}\text { (d) } \mathrm{Pr}^{3+} & \text { (s) Coloured glases for gog- } \\ \text { gles. }\end{array}\) \\ \hline \end{tabular}

Step-by-Step Solution

Answer

(a) with (p), (b) with (q), (c) with (r), (d) with (s).

Step 1: Understand the Options

Look at each ion in Column I and its corresponding description in Column II. We need to assign the most appropriate description to each ion.

Step 2: Match \\(\mathrm{Ce}^{4+}\\) with Column II

Cerium(IV) or \(\mathrm{Ce}^{4+}\) is known for being a strong oxidizing agent, especially in volumetric analysis. Therefore, match it with (p) Oxidizing agent in volumetric analysis.

Step 3: Match \\(\mathrm{Nd}^{3+}\\) with Column II

Neodymium(III) or \(\mathrm{Nd}^{3+}\) is often used in misch metal, an alloy consisting of rare earth elements. Match it with (q) Misch metal.

Step 4: Match \\(\mathrm{La}^{3+}\\) with Column II

Lanthanum(III) or \(\mathrm{La}^{3+}\) tends to form colorless compounds or salts. Match it with (r) Colourless salts.

Step 5: Match \\(\mathrm{Pr}^{3+}\\) with Column II

Praseodymium(III) or \(\mathrm{Pr}^{3+}\) is used to color glass, particularly goggles, with its characteristic green color. Match it with (s) Coloured glasses for goggles.

Key Concepts

Oxidizing Agent

In chemistry, an oxidizing agent is a substance that can accept electrons and, in doing so, often releases oxygen or another electronegative element. This process makes the oxidizing agent essential in chemical reactions known as oxidation-reduction or redox reactions. During these reactions, the oxidizing agent undergoes a reduction because it gains electrons. Such agents are not only pivotal in various laboratory analyses but also in many industrial applications. Cerium(IV), denoted as \(\mathrm{Ce}^{4+}\), is a commonly used oxidizing agent in volumetric analysis due to its high oxidation potential. This makes it effective in titration processes where precise measurement of reactants is necessary.

• Oxidizing agents play a crucial role in removing electrons from other substances.
• They are vital in laboratory titrations, helping to quantify unknown solutions.

Lanthanides

The lanthanides consist of 15 chemical elements in the periodic table, specifically ranging from atomic numbers 57 through 71, starting with lanthanum. These elements are commonly referred to as rare earth elements, though some are more abundant in the Earth's crust than others. Lanthanides are known for having unpaired 4f electrons, contributing to their unique properties like magnetism and their ability to produce color in compounds.
Neodymium (\(\mathrm{Nd}^{3+}\)) is often used in alloys such as misch metal, which is employed in making strong permanent magnets and sometimes in lighter flints due to its excellent pyrophoric properties. Lanthanum (\(\mathrm{La}^{3+}\)), however, tends to form colorless salts, making it ideal for applications where coloration of compounds is undesired.

• The lanthanides exhibit unique electronic configurations leading to their varied chemical and physical properties.
• They are used in high-tech applications, including lasers, magnets, and phosphors.

Volumetric Analysis

Volumetric analysis is a quantitative analytical method used to determine the concentration of an unknown solution by reacting it with a standard solution. One of the key utilities of volumetric analysis is its ability to provide precise concentration measurements, which are critical for research and industrial processes involving chemical reactions.
In volumetric titrations, solutions of known concentration, known as titrants, are added to a known volume of the sample solution until the reaction reaches completion, often indicated by a color change due to an indicator or the use of an instrument. \(\mathrm{Ce}^{4+}\) as an oxidizing agent is particularly useful in volumetric analysis owing to its capacity to facilitate electron transfer efficiently, thereby helping in determining the concentration of various analytes.

• It is a core technique in laboratories for measuring substance concentrations.
• The end point of a titration can be detected visually or using electronic indicators.

Color Chemistry

Color chemistry explores the role of electron transitions in absorbing and reflecting light, giving compounds and materials their characteristic colors. This field is crucial for developing dyes, pigments, and understanding the color properties of materials. Lanthanide elements like praseodymium (\(\mathrm{Pr}^{3+}\)) are especially noteworthy because their electronic transitions can produce vivid colors. Praseodymium is used to color glasses green, which can be particularly useful in goggles for its ability to filter certain wavelengths of light, enhancing contrast and providing protection.

The study of color chemistry relies heavily on understanding how different materials absorb certain wavelengths of light and emit others. Transition elements and lanthanides are often involved in creating vibrant hues, due to their complex electron structures.

• Colors are due to the absorption of specific light wavelengths and emission of others.
• Lanthanide elements are integral in industries requiring specific color properties.