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

Question

Identify the incorrect statement among the following: (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

Statement (b) is incorrect as it should produce ammonium chloride, not hydrochloric acid.

Step 1: Understand the Statements

Read each statement carefully and understand the chemical reactions they describe. We need to determine if each reaction is valid according to chemical principles and known chemical reactions.

Step 2: Review Statement (a)

Statement (a) involves the reaction of silicon with sodium hydroxide and air. This reaction is plausible. Silicon can react with sodium hydroxide in an alkaline medium to form sodium silicate (\(\mathrm{Na}_{2}\mathrm{SiO}_{3}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). Thus, statement (a) is correct.

Step 3: Review Statement (b)

Statement (b) involves the reaction of chlorine (\(\mathrm{Cl}_{2}\)) with excess ammonia (\(\mathrm{NH}_{3}\)) to produce nitrogen (\(\mathrm{N}_{2}\)) and hydrochloric acid (\(\mathrm{HCl}\)). This is a known reaction: chlorine reacts with ammonia to form nitrogen and ammonium chloride, not hydrochloric acid. This statement is incorrect because it's not \(\mathrm{HCl}\) that is formed, but \(\mathrm{NH}_{4}\mathrm{Cl}\).

Step 4: Review Statement (c)

Statement (c) states that bromine reacts with hot, concentrated sodium hydroxide to produce sodium bromide (\(\mathrm{NaBr}\)), sodium perbromate (\(\mathrm{NaBrO}_{4}\)), and water (\(\mathrm{H}_{2}\mathrm{O}\)). Normally, the reaction produces sodium bromide (\(\mathrm{NaBr}\)) and sodium hypobromite (\(\mathrm{NaBrO}\)), not perbromate. Thus, statement (c) is incorrect.

Step 5: Review Statement (d)

Statement (d) states that ozone reacts with sulfur dioxide to form sulfur trioxide. This is a correct statement; ozone acts as an oxidizing agent converting sulfur dioxide (\(\mathrm{SO}_{2}\)) into sulfur trioxide (\(\mathrm{SO}_{3}\)).

Key Concepts

Silicon and Sodium Hydroxide Reaction

The reaction between silicon (Si) and sodium hydroxide (NaOH) in the presence of air is a classic example of an inorganic chemistry reaction. Silicon is a metalloid, and it does not dissolve in water but reacts with alkalis like sodium hydroxide under specific conditions. When the reaction occurs:

• Silicon reacts with sodium hydroxide in an aqueous solution, facilitated by the presence of oxygen from the air.
• This leads to the formation of sodium silicate (\( \mathrm{Na}_2\mathrm{SiO}_3 \)) and water (\( \mathrm{H}_2\mathrm{O} \)).

This reaction is significant because it demonstrates a key property of silicon—that it can engage in reactions with bases to form silicates. This property is crucial in various industrial applications, including the production of glasses and ceramics.

Chlorine and Ammonia Reaction

Chlorine (\( \mathrm{Cl}_2 \)) reacts with ammonia (\( \mathrm{NH}_3 \)) in a highly exothermic reaction that is often used in the production of nitrogen and ammonium chloride. However, it is important to differentiate the products formed under excess ammonia condition:

• With excess \( \mathrm{NH}_3 \), chlorine reacts to produce nitrogen (\( \mathrm{N}_2 \)) and ammonium chloride (\( \mathrm{NH}_4\mathrm{Cl} \)), not hydrochloric acid (\( \mathrm{HCl} \)).
• The correct balanced equation is:\[ 3\mathrm{Cl}_2 + 8\mathrm{NH}_3 \rightarrow 6\mathrm{NH}_4\mathrm{Cl} + \mathrm{N}_2 \]

This clear understanding of the reaction is vital because \( \mathrm{NH}_4\mathrm{Cl} \) is a significant compound with uses ranging from fertilizers to acidity regulation in food processing.

Bromine and Sodium Hydroxide Reaction

The reaction of bromine (\( \mathrm{Br}_2 \)) with hot and concentrated sodium hydroxide (\( \mathrm{NaOH} \)) is another interesting example of inorganic reaction mechanisms that produces unusual compounds.

• When bromine reacts with sodium hydroxide, the reaction produces sodium bromide (\( \mathrm{NaBr} \)) and sodium hypobromite (\( \mathrm{NaBrO} \)). However, a common misconception is the production of sodium perbromate (\( \mathrm{NaBrO}_4 \)), which is incorrect.
• The reaction proceeds as follows:\[ \mathrm{Br}_2 + 2\mathrm{NaOH} \rightarrow \mathrm{NaBr} + \mathrm{NaBrO} + \mathrm{H}_2\mathrm{O} \]

Understanding these chemical dynamics is important for students as it lays down the foundational knowledge for predicting products in various oxidation and reduction scenarios involving halogens and alkalis.