Gases Generated In A Chemical Reactions Are Sometimes Collected By Displacement Of Water,as Shown Above

Gases Generated In A Chemical Reactions Are Sometimes Collected By Displacement Of Water, as Shown Above

Understanding how gases are collected during chemical reactions is fundamental in chemistry. One common method involves the displacement of water, which allows scientists to safely and accurately gather gases produced in reactions. This technique is especially useful when dealing with gases that are insoluble or only slightly soluble in water, ensuring pure gas collection for further analysis. In this article, we will explore the principles behind the displacement of water method, its applications, procedures, advantages, limitations, and examples to enhance your understanding of this essential laboratory technique.

Principle Behind Collection of Gases by Displacement of Water

The displacement of water method relies on the fact that many gases are insoluble or only sparingly soluble in water, allowing them to be collected without dissolving significantly. When a gas is generated in a reaction vessel, it can be channeled into an inverted water-filled container (usually a trough or a jar), which is submerged in water. Since water is nearly incompressible and the gas is less dense than water, the gas displaces the water in the container, allowing for its collection and measurement.

Key Principles:

• Insolubility of the Gas: The gas must not dissolve significantly in water to avoid contamination.


• Density of the Gas: Gases lighter than air (like hydrogen and helium) can be collected by displacement of water.


• Non-reactivity: The gas should not react with water or the container material.


• Sealed System: To prevent gas escape, the system must be airtight once the gas displaces the water.

Applications of Displacement of Water Method

This technique is widely used in various laboratory and industrial processes, including:

1. Hydrogen Gas Collection

Hydrogen gas is often generated via reactions like the zinc and hydrochloric acid reaction. Its collection through water displacement is standard due to its insolubility and lightness.

2. Oxygen Gas Collection

Oxygen produced from decomposition of potassium chlorate or other reactions can be collected similarly, provided it does not react with water.

3. Carbon Dioxide Collection

Although carbon dioxide is more soluble in water, it can sometimes be collected by displacement of water if proper precautions are taken, especially when pure samples are needed.

4. Gases in Industrial Processes

Industries often use water displacement to collect gases like ammonia or inert gases, provided they are compatible with water.

Procedure for Collecting Gases by Displacement of Water

The collection process involves several carefully executed steps to ensure safety and accuracy:

Materials Needed:

• Gas generation apparatus (e.g., test tube, flask)
• Delivery tube or delivery pipe
• Water trough or basin
• Collection jar or container (preferably an inverted glass jar or bottle)
• Clamp stand
• Water
• Gas-tight seal or rubber stoppers

Step-by-Step Process:

1. Set Up the Apparatus:

• Fill the water trough with clean water.
• Fill the collection jar completely with water and invert it carefully without trapping air.
• Place the inverted jar into the water trough, ensuring it is submerged and water-tight.

1. Connect the Gas Source:

• Attach the delivery tube to the reaction vessel generating the gas.
• Connect the other end of the delivery tube to the mouth of the inverted jar, ensuring a secure seal with rubber stoppers if necessary.

1. Initiate the Reaction:

• Carry out the chemical reaction carefully, observing safety precautions.
• As the gas is produced, it travels through the delivery tube and displaces the water in the inverted jar.

1. Collect the Gas:

• The gas fills the jar, pushing out the water.
• Once the jar is filled with the gas, stop the reaction or seal the jar to prevent gas escape.

1. Measurement and Analysis:

• The volume of gas can be measured by noting the level of water displaced or by using graduated collection jars.
• Proceed with further tests or experiments as required.

Advantages of Collecting Gases by Displacement of Water

This method offers several benefits, making it a popular choice in laboratory settings:

• Simplicity: The setup is straightforward and easy to assemble.


• Safety: It minimizes exposure to hazardous gases when properly handled.


• Purity of Gas: The method allows collection of relatively pure gases free from contamination.


• Cost-Effective: Requires minimal expensive equipment.

Limitations and Precautions

Despite its advantages, the displacement of water method has certain limitations:

Limitations:

• Solubility Issues: Gases like carbon dioxide and ammonia dissolve in water, which can lead to underestimation of volume.
• Reactivity: Gases reactive with water (e.g., chlorine, sulfur dioxide) cannot be collected using this method.
• Density Considerations: Heavier gases (like carbon dioxide) may dissolve more readily, affecting collection efficiency.
• Leakage: Ensuring airtight seals is crucial; leaks can lead to loss of gas and inaccurate results.

Precautions:

• Use appropriate safety gear, including gloves and goggles.
• Ensure the apparatus is airtight to prevent gas escape.
• Use water that is free of impurities.
• Be cautious with reactive gases; conduct reactions in well-ventilated areas or under fume hoods.

Examples of Gases Collected by Displacement of Water

Understanding practical examples helps reinforce the concept:

Example 1: Collection of Hydrogen Gas

• Reaction: Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
• Process: Hydrogen gas generated in a test tube is directed into an inverted jar filled with water, displacing the water and collecting hydrogen.

Example 2: Collection of Oxygen Gas

• Reaction: Decomposition of potassium chlorate using heat
• Process: Oxygen released is collected by displacement of water in a similar setup.

Example 3: Collection of Carbon Dioxide

• Reaction: Reaction of calcium carbonate with hydrochloric acid
• Process: Carbon dioxide produced is collected by displacement of water, provided measures are taken to minimize its solubility issues.

Alternative Methods of Gas Collection

While displacement of water is common, other techniques include:

• Displacement of Air: Suitable for gases insoluble or reactive with water.


• Using Gas Syringes: For small quantities and gases that are soluble or reactive.


• Direct Collection: In some industrial settings, gases are directly transported through pipelines.

Conclusion

The displacement of water remains an essential and versatile technique for collecting gases generated during chemical reactions. Its simplicity, safety, and effectiveness make it a preferred method in educational laboratories and research settings. Understanding the principles, proper setup, and limitations of this technique ensures accurate data collection and safe handling of gases. Whether collecting hydrogen, oxygen, or other gases, mastering this method is fundamental for chemistry students and professionals alike.

Summary:

• Gases are collected by displacing water when they are insoluble and less dense than water.


• Proper setup and safety precautions are crucial.


• The method is widely applicable but has limitations with soluble and reactive gases.


• Alternative methods exist for specific gases or conditions.


• Practical applications include hydrogen, oxygen, and carbon dioxide collection.

By mastering the displacement of water technique, chemists can confidently analyze gaseous products of reactions, contributing to advancements in research, industry, and education.