Problem 38 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following oxides of nitrogen is a coloured gas? [1987-1 Mark] (a) \(\mathrm{N}_{2} \mathrm{O}\) (b) \(\mathrm{NO}\) (c) \(\mathrm{N}_{2} \mathrm{O}_{5}\) (d) \(\mathrm{NO}_{2}\)

Step-by-Step Solution

Answer

The colored gas is \( \mathrm{NO}_{2} \).

Step 1: Identify the Color of Each Oxide

Before determining which oxide is a colored gas, we must identify the characteristic color for each nitrogen oxide listed. - \( \mathrm{N}_{2} \mathrm{O} \) (Nitrous oxide) is a colorless gas.- \( \mathrm{NO} \) (Nitric oxide) is also colorless.- \( \mathrm{N}_{2} \mathrm{O}_{5} \) is a colorless solid at room temperature, not a gas.- \( \mathrm{NO}_{2} \) (Nitrogen dioxide) is a reddish-brown gas.

Step 2: Determine State of Each Compound

Check whether each compound is typically found as a gas under standard conditions. - \( \mathrm{N}_{2} \mathrm{O} \) and \( \mathrm{NO} \) are gases at room temperature.- \( \mathrm{N}_{2} \mathrm{O}_{5} \) is a solid, thus not a gaseous oxide.- \( \mathrm{NO}_{2} \) is a gas at room temperature and has a color.

Step 3: Conclusion Based on Observations

From the observations, the only colored gas among the choices is \( \mathrm{NO}_{2} \), which is known for its distinctive reddish-brown color.

Key Concepts

Gas properties

Gases are fascinating, and their properties are diverse. When studying gases, it is important to note their physical state under standard conditions. Standard conditions usually imply room temperature and atmospheric pressure. Most gases, like seen in the exercise, have distinctive properties.

• Many gases are colorless, which makes them hard to distinguish by sight alone, like oxygen or nitrogen.
• Some gases have distinct smells, which help us identify them even if they're not visible.
• Pressure and temperature also impact gas behavior significantly; for example, some substances are gases at room temperature but become liquids or solids if cooled or pressurized.

Gases like nitrogen dioxide exhibit unique characteristics, including color, which make them stand out compared to other typically colorless gases. Understanding these gas properties helps chemists identify and use gases effectively in various applications.

Colored gases

Most gases are invisible with no distinct color. However, there are exceptions, with some gases having a unique coloration that helps in their identification. Colored gases can sometimes pose health hazards because certain colored gases indicate chemical reactivity. Nitrogen dioxide ( NO_{2} ) is a classic example of a colored gas. Its reddish-brown appearance is due to its absorption of visible light in a particular way. Other gases like chlorine have a greenish-yellow color.

• These colors generally arise due to the specific electronic transitions within the molecules, impacting how they absorb and emit light.
• Monitoring these colors can aid in detecting leaks or contamination.

Being aware of the colors can also play a critical role in preventing exposure to harmful gases, thereby ensuring safety in both industrial and laboratory settings.

Nitrogen dioxide

Nitrogen dioxide, often represented by the chemical formula NO_{2} , is a reddish-brown gas. It has important environmental and industrial significance. This gas is a major air pollutant, primarily produced from combustion, like vehicle emissions and power plants.

• Nitrogen dioxide is a reactive gas and plays a significant role in atmospheric reactions, such as forming acid rain and contributing to smog.
• Its presence in the atmosphere affects air quality and poses health risks like respiratory problems when inhaled in large quantities.

In terms of industrial application, nitric acid production heavily relies on nitrogen dioxide. Recognizing its distinct reddish-brown color helps in detecting its presence, which is essential both for industrial processes and when assessing air quality.