Question

Nitrogen dioxide cannot be prepared by heating (a) \(\mathrm{KNO}_{3}\) (b) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (d) \(\mathrm{AgNO}_{3}\)

Short answer

Option (a):  ext{KNO}_{3} does not form nitrogen dioxide on heating.

Step-by-step solution

Understand the Reaction

To solve this problem, we need to understand what happens when these compounds decompose with heat. Each of these metal nitrates can decompose to give different gases.

Identify Reaction Products

When heated, potassium nitrate (mathrm{KNO_{3}}) typically decomposes to form potassium nitrite (mathrm{KNO_{2}}) and oxygen. This reaction does not produce  ext{NO}_{2}. The other reactions generally produce nitrogen dioxide ( ext{NO}_{2}) as a product.

Determine the Correct Option

Based on the reactions, only  ext{KNO}_{3} does not produce nitrogen dioxide ( ext{NO}_{2}) when decomposed by heating. The others do produce  ext{NO}_{2}. Therefore, the correct answer is option (a).

Verify with Chemical Equations

To verify, consider typical decomposition reactions: -  ext{Pb} ext{(NO}_{3} ext{)}_{2}) decomposes to form  ext{PbO} + 2 ext{NO}_{2} + ext{O}_{2}. -  ext{Cu} ext{(NO}_{3} ext{)}_{2}) decomposes to form  ext{CuO} + 2 ext{NO}_{2} + ext{O}_{2}. -  ext{AgNO}_{3} decomposes to form  ext{Ag} + ext{NO}_{2} + ext{O}_{2}. - Compared to:  ext{2KNO}_{3} ightarrow 2 ext{KNO}_{2} + ext{O}_{2}. This confirms that  ext{KNO}_{3} does not release  ext{NO}_{2}.

Key concepts

Nitrogen Dioxide Production

Nitrogen dioxide ( NO_2 ) is an important gas, often encountered in atmospheric chemistry and various industrial reactions. It is a reddish-brown gas with a characteristic sharp, biting odor and is a significant air pollutant.
To understand the production of nitrogen dioxide, it's crucial to know about thermal decomposition reactions involving metal nitrates. When certain metal nitrates are heated, they decompose to produce nitrogen dioxide as one of the products.
However, not all metal nitrates undergo such a decomposition that yields NO_2 . Potassium nitrate ( KNO_3 ) is a notable exception, generally producing potassium nitrite ( KNO_2 ) and oxygen ( O_2 ) instead of nitrogen dioxide. This unique behavior makes potassium nitrate different in the context of nitrogen dioxide production from thermal decomposition.

• Nitrogen dioxide is a major component of smog.
• It is hazardous to health, contributing to respiratory problems.
• Understanding its formation is vital for environmental and industrial contexts.

Metal Nitrates Decomposition

When metal nitrates undergo thermal decomposition, they often produce different gases, depending on the specific metal nitrate in question. The general formula for the reaction involves breaking down into a metal oxide, nitrogen dioxide ( NO_2 ), and oxygen ( O_2 ). However, the specific products can vary based on the metal involved. Here are some examples:

• Lead nitrate ( Pb(NO_3)_2 ) decomposes to produce lead oxide ( PbO ), nitrogen dioxide ( 2NO_2 ), and oxygen ( O_2 ).
• Copper(II) nitrate ( Cu(NO_3)_2 ) decomposes to form copper(II) oxide ( CuO ), nitrogen dioxide ( 2NO_2 ), and oxygen ( O_2 ).
• Silver nitrate ( AgNO_3 ) decomposes at even lower temperatures to produce silver ( Ag ), nitrogen dioxide ( NO_2 ), and oxygen ( O_2 ).

Each decomposition has its own temperature stability and reaction conditions. The process highlights the chemistry of metal nitrates and provides insight into their thermal stability and reactivity.

Thermal Decomposition Reactions

Thermal decomposition is a common type of chemical reaction where a compound breaks down into two or more components due to heating. This process is critical in various industrial applications and scientific studies.
The concept is particularly fascinating when applied to metal nitrates, which are notorious for their ability to decompose into metals, nitrogen dioxide, and oxygen gases. Unlike other reactions, thermal decomposition does not require any external reagents apart from heat.
Key points about thermal decomposition reactions:

• They are generally endothermic, requiring heat to proceed.
• The products often include gases, making them useful in gas generation.
• The decomposition temperature will vary based on the compound's stability.

Understanding these reactions is imperative for science students as they demonstrate the interplay between heat and chemical stability. It also provides a practical learning ground for observing reaction mechanisms firsthand.