Problem 211 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the incorrect statement among the following: [2007] (a) silicon reacts with \(\mathrm{NaOH}\) (aq) in the presence of air to give \(\mathrm{Na}_{2} \mathrm{SiO}_{3}\) and \(\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Cl}_{2}\) reacts with excess of \(\mathrm{NH}_{3}\) to give \(\mathrm{N}_{2}\) and \(\mathrm{HCl}\) (c) \(\mathrm{Br}_{2}\) reacts with hot and strong \(\mathrm{NaOH}\) solution to give \(\mathrm{NaBr}, \mathrm{NaBrO}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) (d) ozone reacts with \(\mathrm{SO}_{2}\) to give \(\mathrm{SO}_{3}\)

Step-by-Step Solution

Answer

The incorrect statement is (c).

Step 1: Analyze Reaction (a)

The reaction given is silicon reacting with aqueous sodium hydroxide (\( \mathrm{NaOH} \)) in the presence of air to yield sodium silicate (\( \mathrm{Na}_{2} \mathrm{SiO}_{3} \)) and water. This is a correct statement and one of the classic reactions of silicon.

Step 2: Analyze Reaction (b)

The reaction described is chlorine (\(\mathrm{Cl}_{2} \)) reacting with excess ammonia (\(\mathrm{NH}_{3} \)) to form nitrogen (\(\mathrm{N}_{2} \)) and hydrochloric acid (\(\mathrm{HCl} \)). This statement is correct, and the balanced reaction is \( 3\mathrm{Cl}_{2} + 8\mathrm{NH}_{3} \rightarrow 6\mathrm{NH}_{4}\mathrm{Cl} + \mathrm{N}_{2} \).

Step 3: Analyze Reaction (c)

This states that bromine (\(\mathrm{Br}_{2} \)) reacts with hot and strong sodium hydroxide to form \(\mathrm{NaBr}, \mathrm{NaBrO}_{4}, \) and water. Upon examining the actual reaction, it is found that \(\mathrm{NaBr} \) and \(\mathrm{NaBrO}_{3} \) are produced, not \(\mathrm{NaBrO}_{4} \). This makes the statement incorrect.

Step 4: Analyze Reaction (d)

The statement here is that ozone (\(\mathrm{O}_3 \)) reacts with sulfur dioxide (\(\mathrm{SO}_{2} \)) to form sulfur trioxide (\(\mathrm{SO}_{3} \)). This reaction is accurate and commonly used to reduce \(\mathrm{SO}_{2} \) pollution.

Key Concepts

Silicon Reactions

Silicon, a fascinating element in the field of inorganic chemistry, exhibits interesting reactivity behaviors. One of the significant reactions involves its interaction with aqueous sodium hydroxide (\( \mathrm{NaOH} \)) in the presence of air. In this process, silicon reacts to form sodium silicate (\( \mathrm{Na}_{2} \mathrm{SiO}_{3} \)) and water (\( \mathrm{H}_{2} \mathrm{O} \)). This reaction highlights silicon's ability to form complex silicate compounds, which are fundamental in various industrial applications.

• Sodium silicate has a wide range of uses, from detergents to the consolidation of loose dust in roads.
• Another product, water, signifies the consumptive use of oxygen from air in this reaction, showcasing silicon's affinity to combine with oxygen and alkaline environments.

Understanding these properties is crucial for grasping silicon’s role in glass production and its implications in the electronics industry as a key semiconductor.

Chlorine Chemistry

Chlorine exhibits fascinating chemistry, particularly when reacting with ammonia (\( \mathrm{NH}_{3} \)). When chlorine (\( \mathrm{Cl}_{2} \)) is mixed with excess ammonia, a crucial chemical transformation occurs, yielding nitrogen (\( \mathrm{N}_{2} \)) and hydrochloric acid (\( \mathrm{HCl} \)). The balanced equation \( 3\mathrm{Cl}_{2} + 8\mathrm{NH}_{3} \rightarrow 6\mathrm{NH}_{4}\mathrm{Cl} + \mathrm{N}_{2} \) shows the stoichiometry of the reaction.

• Chlorine is a powerful oxidizing agent, and its ability to transform ammonia exemplifies its reactivity, especially in producing nitrogen, an inert and stable molecule.
• The formation of ammonium chloride (\( \mathrm{NH}_{4}\mathrm{Cl} \)) showcases chlorine's versatility in forming salt-like structures.

This interaction is pivotal in various industrial processes, including fertilizers and explosive compounds, emphasizing chlorine's multifaceted role in chemistry.

Bromine Reactions

Bromine is known for its reactivity, especially when combined with strong bases. When bromine (\( \mathrm{Br}_{2} \)) is introduced to hot, concentrated sodium hydroxide (\( \mathrm{NaOH} \)), it results in a series of products: sodium bromide (\( \mathrm{NaBr} \)), sodium bromate (\( \mathrm{NaBrO}_{3} \)), and water. This outcome is due to bromine's unique ability to undergo disproportionation, a reaction where an element is simultaneously oxidized and reduced.

• Disproportionation reactions are critical in identifying bromine's dual nature, where it forms both higher (\( \mathrm{NaBrO}_{3} \)) and lower oxidation state compounds (\( \mathrm{NaBr} \)).
• These reactions illustrate bromine's adaptability in different chemical environments.

Understanding these reactions provides insight into bromine's chemical behavior and its applications, notably in dyeing and bleaches.

Ozone and Sulfur Dioxide

Ozone (\( \mathrm{O}_3 \)) and sulfur dioxide (\( \mathrm{SO}_{2} \)) engage in an important reaction to form sulfur trioxide (\( \mathrm{SO}_{3} \)). This transformation is significant in environmental chemistry and pollution control. Sulfur trioxide subsequently reacts with water to form sulfuric acid (\( \mathrm{H}_{2}\mathrm{SO}_{4} \)), a crucial chemical in industry.

• Ozone acts as a potent oxidizing agent, offering an effective method to oxidize sulfur dioxide in controlled conditions.
• This reaction not only underscores ozone's role in atmospheric chemistry but also its utility in mitigating environmental pollution, particularly reducing the harmful effects of \( \mathrm{SO}_{2} \).

By understanding this chemical process, scientists can develop strategies for pollution abatement and better manage air quality.