Acids, Bases and Salts | Lecture 5 | Chapter 1 | Class 10 | Science Term -1 CBSE | Free Education

Summary

The video explores a chemistry experiment focused on the acidic behavior of hydrochloric acid (HCl) gas. It demonstrates how dry and wet litmus paper react when exposed to HCl gas. The dry litmus paper shows no color change because the HCl gas is not acidic without water. However, wet litmus paper turns red as the HCl gas dissolves in the water, acquiring its acidic nature. The video emphasizes the importance of controlling humidity during the experiment and explains how a drying tube with calcium chloride can ensure accurate results by removing moisture from the air.

Takeaways

• 😀 HCl gas does not show acidic properties when dry, as it doesn't react with litmus paper.
• 😀 Wet litmus paper turns red when exposed to HCl gas, indicating that the gas has dissolved in water and acquired acidic properties.
• 😀 The acidity of HCl gas is only visible when it comes into contact with water, which helps it exhibit acidic behavior.
• 😀 Dry litmus paper does not change color when exposed to dry HCl gas, proving that the gas alone is not acidic.
• 😀 The presence of humidity in the air can cause the dry HCl gas to react with water vapor, leading to color change in the litmus paper.
• 😀 If high humidity is present during the experiment, both dry and wet litmus papers could turn red, resulting in inaccurate conclusions.
• 😀 To prevent false results due to humidity, a drying tube (or guard tube) is used to ensure that only dry HCl gas is tested.
• 😀 The drying tube contains calcium chloride, which absorbs water vapor from the air, preventing contamination of the HCl gas.
• 😀 The experiment requires careful control of external factors, like humidity, to achieve accurate results.
• 😀 The main goal of the experiment is to show how HCl gas behaves in different conditions, particularly how it interacts with litmus paper to indicate acidity.

Q & A

What does the experiment aim to demonstrate?

The experiment demonstrates how HCl gas interacts with litmus paper to show its acidic behavior when dissolved in water.

Why does dry HCl gas not change the color of litmus paper?

Dry HCl gas does not exhibit acidic behavior, which is why it does not alter the color of the litmus paper. It requires dissolution in water to show its acidic properties.

What happens when HCl gas dissolves in water?

When HCl gas dissolves in water, it acquires an acidic nature, dissociates to form H⁺ ions, and can turn litmus paper red.

What is the role of wet litmus paper in the experiment?

Wet litmus paper allows HCl gas to dissolve in the water, thereby exhibiting its acidic nature and turning the litmus paper red.

How does HCl gas demonstrate its acidic nature?

HCl gas demonstrates its acidic nature by dissolving in water to form hydrogen ions (H⁺), which causes the litmus paper to turn red.

What can cause an incorrect result in the experiment, where both dry litmus papers turn red?

High humidity in the air can cause both dry litmus papers to turn red, as the water vapor in the air can mix with HCl gas, making it acidic before reaching the litmus paper.

How can humidity affect the results of the experiment?

Humidity can cause atmospheric water vapor to mix with HCl gas, which leads to the gas becoming acidic and turning the dry litmus paper red even before it dissolves in water.

What is the solution to avoid humidity affecting the experiment?

The solution is to use a drying tube or guard tube, which contains calcium chloride to absorb water vapor and ensure that only dry HCl gas reaches the litmus paper.

What is the function of the drying tube in the experiment?

The drying tube absorbs water vapor from the air, ensuring that only dry HCl gas reaches the litmus paper, preventing incorrect results due to high humidity.

Why does the litmus paper turn red in the presence of acidic substances?

Litmus paper turns red in the presence of acidic substances because the hydrogen ions (H⁺) in the acid cause a chemical reaction with the dye in the litmus paper, changing its color.