Problem 139 - A Complete Resource Book in Chemistry for JEE Main

Question

Brown vapours can be of (a) \(\mathrm{Br}_{2}\) (b) \(\mathrm{NO}_{2}\) (c) \(\mathrm{HCl}\) (d) \(\mathrm{HBr}\)

Step-by-Step Solution

Answer

Brown vapors can be of  extbf{Br}_2) and  extbf{NO}_2).

Step 1: Identify substance descriptions

Research and identify the color of vapors for each of the given substances. 1. Bromine () has red-brown vapors. 2. Nitrogen dioxide () isa gas that is brown in color. 3. Hydrogen chloride () is a colorless gas. 4. Hydrogen bromide () is also a colorless gas.

Step 2: Determine the color associated with the options

From Step 1, note the color of the vapors: -  extbf{Br}_2) has red-brown vapors. -  extbf{NO}_2) has brown vapors. -  extbf{HCl}) is colorless. -  extbf extbf{HBr}) is colorless.

Step 3: Identify the substances that produce brown vapors

Based on the information gathered, identify which substances produce brown vapors: -  extbf{Br}_2), which has red-brown vapors, can be considered as producing brown vapors. -  extbf{NO}_2) clearly produces brown vapors.

Step 4: Conclusion

The substances with brown vapors from the given options are  extbf{Br}_2) and  extbf{NO}_2).

Key Concepts

Bromine Vapours

Bromine is a fascinating element that stands out due to its unique appearance. When in a gaseous state, bromine forms red-brown vapours that are easily recognizable. This distinct color is one of the key characteristics that make bromine vapours relatively easy to identify in experiments.

Bromine is a halogen, specifically located in Group 17 of the periodic table. It is one of the few elements that naturally exist as a liquid at room temperature. When this dark reddish-brown liquid is converted into a gas, it maintains its signature red-brown color, which can range from a deep red to a lighter brown shade depending on concentration and lighting conditions.

It's important for students to remember that bromine vapours are not only identified by their color but also by a distinct sharp smell. However, it is crucial to handle bromine with care, as it is a very reactive and potentially dangerous halogen.

Nitrogen Dioxide

Nitrogen Dioxide, or \( ext{NO}_2\), is another compound known for its brown gaseous state. This gas is particularly notorious in urban environments, often found as a pollutant due to vehicle emissions and industrial processes.

In appearance, nitrogen dioxide is a toxic gas with a sharp, unpleasant smell. Its brown coloration makes it easy to spot, especially when present in higher concentrations. This coloration helps in identifying \( ext{NO}_2\) during experiments and in real-world settings where air quality is a concern.

Chemically, \( ext{NO}_2\) plays a significant role in the atmosphere. It interacts with sunlight to form photochemical smog, a common sight in densely populated cities. Students studying environmental science or chemistry should be aware of the factors that lead to the production of this gas, as well as its implications for health and environmental policy.

Colour of Gases

Understanding the color of gases is a fundamental aspect of studying chemistry. Different gases exhibit distinct colors, which can aid in their identification. The presence of color is often due to the way light interacts with the gas molecules. Here are a few points to consider:

• Bromine (Br2): Known for its red-brown vapours, makes it easy to recognize in laboratory settings.
• Nitrogen Dioxide (NO2): Exhibits a clear brown color, especially notable outdoors due to its role in air pollution.
• Hydrogen Chloride (HCl) and Hydrogen Bromide (HBr): Both are colorless, making them less obvious to detect visually without the aid of indicators or chemical tests.

The color of a gas can provide immediate information about the substance in question, allowing for quick identification in many chemical processes. Recognizing these colors can be crucial during chemical analysis and when determining the presence of certain chemicals in the environment. Ultimately, the ability to distinguish between different gas colors enhances a chemist's toolset in both practical and theoretical scenarios.