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 \(\mathrm{N}_{2}\mathrm{O}_{3}\).

Step 1: Understand the Problem

We need to determine which compound is formed as a blue liquid from an equimolar mixture of two gases at -30°C. The options provided are different nitrogen oxides.

Step 2: Identify the Compounds

Examine the compounds: (a) \(\mathrm{N}_{2}\mathrm{O}\) is known as dinitrogen monoxide. (b) \(\mathrm{N}_{2}\mathrm{O}_{3}\) is dinitrogen trioxide. (c) \(\mathrm{N}_{2}\mathrm{O}_{4}\) is dinitrogen tetroxide. (d) \(\mathrm{N}_{2}\mathrm{O}_{5}\) is dinitrogen pentoxide.

Step 3: Determine the Likely Liquid at -30°C

Recall the physical properties of these compounds: 1. \(\mathrm{N}_{2}\mathrm{O}\) (nitrous oxide) is a gas under these conditions.2. \(\mathrm{N}_{2}\mathrm{O}_{3}\) is a liquid at low temperatures, forming from \(\mathrm{NO}\) and \(\mathrm{NO}_{2}\).3. \(\mathrm{N}_{2}\mathrm{O}_{4}\) is colorless or pale yellow, not blue.4. \(\mathrm{N}_{2}\mathrm{O}_{5}\) decomposes easily at ambient conditions, typically solid.

Step 4: Recognize the Blue Liquid

The correct compound, \(\mathrm{N}_{2}\mathrm{O}_{3}\), is known to be a blue liquid at low temperatures. It forms by an equimolar mixture of gases \(\mathrm{NO}\) and \(\mathrm{NO}_{2}\), matching the problem description.

Key Concepts

Chemical Compounds

In the realm of chemistry, a chemical compound is a substance composed of two or more different types of atoms bonded together. Compounds have specific chemical formulas, representing the elements and number of atoms of each element present in a molecule. For example, nitrogen oxides are a group of compounds made of nitrogen (N) and oxygen (O) atoms. These compounds vary in their number of oxygen atoms per nitrogen atom, resulting in different members like

• Dinitrogen monoxide (\(\mathrm{N}_2\mathrm{O}\)) - commonly known as laughing gas.
• Dinitrogen trioxide (\(\mathrm{N}_2\mathrm{O}_3\)) - forms a blue liquid at low temperatures.
• Dinitrogen tetroxide (\(\mathrm{N}_2\mathrm{O}_4\)) - appears colorless or pale yellow.
• Dinitrogen pentoxide (\(\mathrm{N}_2\mathrm{O}_5\)) - often decomposes under mild conditions.

These chemical compounds are often involved in important chemical reactions and can have various industrial and environmental implications.

Physical Properties

Physical properties are characteristics of substances that can be observed without changing their composition. Each molecular structure provides unique attributes like:

• State at Room Temperature: Some nitrogen oxides like \(\mathrm{N}_2\mathrm{O}\) exist as gases, while others, like \(\mathrm{N}_2\mathrm{O}_3\), transform into liquid under specific conditions such as low temperatures.
• Color: Dinitrogen trioxide \(\mathrm{N}_2\mathrm{O}_3\) notably forms a blue liquid, which is an important identifying feature.
• Boiling and Melting Points: These determine the temperatures at which compounds transition between solid, liquid, and gaseous states. The low-temperature stability of \(\mathrm{N}_2\mathrm{O}_3\) allows it to remain liquid at -30°C.
• Volatility: Compounds like \(\mathrm{N}_2\mathrm{O}_5\) can decompose easily, demonstrating their instability in ambient conditions.

Understanding these properties is crucial for predicting how substances react and transform under various conditions.

Chemical Reactions

Chemical reactions involve the transformation of substances by breaking and forming chemical bonds. In the context of nitrogen oxides:

• Formation of Dinitrogen Trioxide: It occurs through the reaction between nitric oxide (\(\mathrm{NO}\)) and nitrogen dioxide (\(\mathrm{NO}_2\)). An equimolar mixture of these gases results in dinitrogen trioxide \(\mathrm{N}_2\mathrm{O}_3\), particularly under cold conditions, forming a blue liquid.
• Decomposition: Some nitrogen oxides, such as \(\mathrm{N}_2\mathrm{O}_5\), are not stable and can break down into simpler components like nitrogen dioxide and oxygen, especially under ambient temperature.
• Environmental Reactions: Nitrogen oxides are significant in atmospheric chemistry, contributing to phenomena like smog formation and acid rain when they react with other environmental components.

Each reaction may drastically change the chemical nature and properties of the substances involved, highlighting the dynamic interactions in chemical compounds.