Problem 70 - A Complete Resource Book in Chemistry for JEE Main

Question

The blue liquid formed by equimolar mixture of two gases at \(-30^{\circ} \mathrm{C}\) is (a) \(\mathrm{N}_{2} \mathrm{O}\) (b) \(\mathrm{N}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{N}_{2} \mathrm{O}_{4}\) (d) \(\mathrm{N}_{2} \mathrm{O}_{5}\)

Step-by-Step Solution

Answer

The blue liquid is  ext{N}_{2} ext{O}_{3}.

Step 1: Identify the Condition

The problem describes a blue liquid formed by an equimolar mixture of two gases at (-30^{ ext{o}} ext{C}). This specific condition will guide us to identify the correct chemical compound.

Step 2: Recall the Chemical Properties

Recall that - extcolor{blue}{ ext{liquid}} ext{-colored liquids at low temperatures are often oxides of nitrogen. ( ext{N}_{2} ext{O}_{3}) is known to be a blue liquid at low temperatures.

Step 3: Evaluate Each Option

Option (a) ext{N}_{2} ext{O} (nitrous oxide) is a colorless gas. Option (b) ext{N}_{2} ext{O}_{3} (dinitrogen trioxide) forms a blue liquid at low temperatures. Option (c) ext{N}_{2} ext{O}_{4} (dinitrogen tetroxide) is typically a colorless or pale yellow liquid. Option (d) ext{N}_{2} ext{O}_{5} (dinitrogen pentoxide) is a solid at room temperature.

Step 4: Determine the Answer

Given that ( ext{N}_{2} ext{O}_{3}) is the only option that forms a blue liquid, the answer to the question is option (b) ext{N}_{2} ext{O}_{3}.

Key Concepts

Nitrogen Oxides

Nitrogen oxides are a group of compounds composed of nitrogen and oxygen. They are prevalent in nature and in the chemical industry.
These compounds vary in their physical and chemical properties. Some form gases, while others form liquids or solids, depending on temperature and pressure conditions.
Common nitrogen oxides include:

• Nitric oxide (\( \text{NO} \))
• Nitrogen dioxide (\( \text{NO}_2 \))
• Nitrous oxide (\( \text{N}_2\text{O} \))
• Dinitrogen trioxide (\( \text{N}_2\text{O}_3 \))
• Dinitrogen tetroxide (\( \text{N}_2\text{O}_4 \))
• Dinitrogen pentoxide (\( \text{N}_2\text{O}_5 \))

These oxides play significant roles in several chemical processes. They are involved in the nitrogen cycle and photochemical smog. Dinitrogen trioxide, for example, is a blue liquid at low temperatures and can act as an oxidative agent.

Chemical Compounds Identification

Identifying chemical compounds involves recognizing their distinct characteristics, such as color, state, and behavior at different temperatures. This process often requires understanding the specific features unique to each compound.
When dealing with nitrogen oxides, different compounds have unique physical attributes:

• Dinitrogen trioxide (\( \text{N}_2\text{O}_3 \)): Notable for forming a blue liquid at low temperatures, distinguishing it from other nitrogen oxides.
• Nitrous oxide (\( \text{N}_2\text{O} \)): A colorless gas, often used as an anesthetic in dental procedures and known as laughing gas.
• Dinitrogen tetroxide (\( \text{N}_2\text{O}_4 \)): Generally appears as a colorless or pale yellow liquid, typically less distinguishable by eye compared to dinitrogen trioxide.
• Dinitrogen pentoxide (\( \text{N}_2\text{O}_5 \)): Usually exists as a solid at room temperature, rather than a liquid or gas.

Recognizing these and other attributes is key to successfully identifying chemical compounds in both experimental and theoretical chemistry.

Temperature Effects on Compounds

Temperature plays a critical role in determining the state and properties of chemical compounds. As temperature changes, so too can a compound's phase and its chemical behavior.
Many nitrogen oxides are particularly sensitive to temperature fluctuations:

• Dinitrogen trioxide (\( \text{N}_2\text{O}_3 \)): Exists as a blue liquid at low temperatures, such as \(-30^{\circ}\text{C}\). However, as the temperature rises, it may become a gas or engage in decomposition.
• Nitrous oxide (\( \text{N}_2\text{O} \)): This compound remains in a gaseous state under typical environmental conditions.
• Dinitrogen tetroxide (\( \text{N}_2\text{O}_4 \)): Changes to a colorless or pale yellow liquid at certain lower temperatures but can revert to nitrogen dioxide (\( \text{NO}_2 \)) as temperatures increase.
• Dinitrogen pentoxide (\( \text{N}_2\text{O}_5 \)): At room temperature, it is solid, but it can melt or decompose at higher temperatures.

Understanding these temperature effects is vital for predicting reactions and stability in chemical processes. It helps chemists to manipulate conditions to yield desired reactions or prevent undesirable ones.