Problem 154 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following (a) \(\mathrm{F}_{2}\) (b) \(\mathrm{Cl}_{2}\) (c) \(\mathrm{Br}_{2}\) (d) \(\mathrm{I}\), Column-II (p) Oxidizing nature (q) Reaction with dil or conc. \(\mathrm{NaOH}\) (r) Pale greenish yellow (s) No bleaching action

Step-by-Step Solution

Answer

(a) - (p), (b) - (r), (c) - (q), (d) - (s)

Step 1: Analyze Column-I

Identify the elements in Column-I. These are diatomic molecules consisting of halogens: (a) \(\mathrm{F}_{2}\) is fluorine.(b) \(\mathrm{Cl}_{2}\) is chlorine.(c) \(\mathrm{Br}_{2}\) is bromine.(d) \(\mathrm{I}_2\) is iodine.

Step 2: Analyze Column-II

Identify the properties in Column-II:(p) Oxidizing nature - All halogens can act as oxidizing agents, but strength decreases down the group.(q) Reaction with dil or conc. \(\mathrm{NaOH}\) - This property is seen in halogens when they react with sodium hydroxide to form halogenated products.(r) Pale greenish yellow - Describes the color of some gaseous halogens.(s) No bleaching action - Indicates the inability to bleach substances.

Step 3: Match Column-I with Column-II

Match each halogen from Column-I to the corresponding property in Column-II:(a) \(\mathrm{F}_{2}\) - Strongest oxidizing agent, reacts vigorously with \(\mathrm{NaOH}\).(b) \(\mathrm{Cl}_{2}\) - Pale greenish yellow gas, capable of bleaching.(c) \(\mathrm{Br}_{2}\) - Weaker oxidizing agent than \(\mathrm{F}_{2}\), interacts with \(\mathrm{NaOH}\), darker color.(d) \(\mathrm{I}_2\) - Least oxidizing and does not bleach, even insoluble in water.

Step 4: Finalize the Matches

Assign the correct matches based on the properties and behavior described:(a) \(\mathrm{F}_{2}\) - \(\text{(p) Oxidizing nature}\)(b) \(\mathrm{Cl}_{2}\) - \(\text{(r) Pale greenish yellow}\)(c) \(\mathrm{Br}_{2}\) - \(\text{(q) Reaction with dil or conc. \(\mathrm{NaOH}\)}\)(d) \(\mathrm{I}_2\) - \(\text{(s) No bleaching action}\)

Key Concepts

Oxidizing Agents

Halogens are known for their strong ability to act as oxidizing agents. As you move up the group in the periodic table, this capability becomes stronger.

• Fluorine ( F_{2} ) is the most powerful oxidizing agent among halogens. It can gain electrons from virtually any substance.
• Chlorine ( Cl_{2} ) is also a strong oxidizer but less so compared to fluorine.
• Bromine ( Br_{2} ) follows, exhibiting moderate oxidizing power.
• Iodine ( I_{2} ) is weak as an oxidizer, yet it can still participate in some redox reactions.

Remember, an oxidizing agent accepts electrons from other species, causing those to reduce while it itself is reduced. This concept is vital for many reactions, such as corrosion and combustion, and holds particular importance in understanding how halogens interact in chemical processes.

Reaction with NaOH

Halogens react differently when mixed with sodium hydroxide ( NaOH ), creating various kinds of products. This process can involve dilution (dil) or concentration (conc) levels of NaOH .

• F_{2} reacts vigorously, leading to many complex products, like NaF and oxygen.
• Cl_{2} , when combined with cold and dilute NaOH , forms bleaching powder, hypo solutions, and other useful chemicals.
• Br_{2} interacts with NaOH to produce unstable hypobromites and more stable bromates.
• I_{2} reacts mildly, producing iodides and iodates in small quantities.

This reactivity is key in many industrial chemical processes, including the production of disinfectants and water treatment chemicals.

Bleaching Properties

The ability of halogens to act as bleaching agents is due to their oxidizing nature. A bleaching agent works by breaking down the compounds that cause color in materials.

• Chlorine ( Cl_{2} ) is well known for its strong bleaching properties. It disrupts chromophores (the colored part of molecules) in fabrics and paper, helping to whiten them.
• Fluorine ( F_{2} ) can bleach, but its extreme reactivity makes it less practical.
• Bromine ( Br_{2} ) bleaches less effectively and is rarely used for this purpose.
• Iodine ( I_{2} ) lacks typical bleaching properties. Therefore, it is not applied in bleaching processes.

Understanding bleaching mechanisms helps in textile and paper industries, where the removal of unwanted colors is essential.

Halogen Colors

Each halogen has a distinct color, largely due to electronic transitions within the molecule. This gives them unique visual properties.

• Fluorine ( F_{2} ) appears pale yellow.
• Chlorine ( Cl_{2} ) is pale greenish-yellow and the most easily recognizable due to its color.
• Bromine ( Br_{2} ) shows a deep reddish-brown color.
• Iodine ( I_{2} ) presents as a dark purple or black solid, though it can appear violet in gaseous form.

Color identification of halogens is commonly used in laboratories to confirm the presence of these elements and understand their reactions with other substances.