Testing for Hydrogen, Oxygen, Carbon Dioxide, Ammonia and Chlorine | Tests | Chemistry | FuseSchool

Summary

In this lesson, we explore how to test for the presence of hydrogen, oxygen, carbon dioxide, ammonia, and chlorine gases in a laboratory. The tests include observing a 'squeaky pop' sound for hydrogen, relighting a glowing splint for oxygen, and using limewater to detect carbon dioxide. Ammonia is identified through a color change in litmus paper and white smoke formation with hydrochloric acid. Chlorine turns litmus paper red and bleaches it. The lesson highlights the distinctive reactions of these gases and their unique properties, aiding in their identification through simple laboratory tests.

Takeaways

• 😀 Testing for gases is important because gases are often colorless and odorless, making them hard to identify.
• 😀 Hydrogen can be tested by placing a lit splint at the mouth of the reaction vessel, which will produce a 'squeaky pop' sound due to combustion.
• 😀 Oxygen can be tested by placing a glowing splint at the mouth of the reaction vessel, where it will relight due to the higher concentration of oxygen.
• 😀 Carbon dioxide extinguishes a lit splint, and a more accurate test is to bubble it through limewater, which turns milky due to the formation of calcium carbonate.
• 😀 Ammonia extinguishes a lit splint and turns damp red litmus paper blue.
• 😀 Ammonia also forms a white smoke of ammonium chloride when exposed to concentrated hydrochloric acid.
• 😀 Chlorine turns damp blue litmus paper red and eventually bleaches it white.
• 😀 Hydrogen burns with a 'squeaky pop' because it undergoes combustion in the presence of oxygen, creating water.
• 😀 The glowing splint relights in oxygen because oxygen supports combustion and is in higher concentration than in air (21%).
• 😀 Carbon dioxide turning limewater milky confirms its presence due to the formation of calcium carbonate.
• 😀 Chlorine's reaction with damp litmus paper, turning it red and bleaching it white, helps confirm its presence.

Q & A

Why is it nearly impossible to determine the identity of a gas just by its appearance?

Because many gases, such as hydrogen, oxygen, and carbon dioxide, are colourless and odourless, making it difficult to distinguish them by sight or smell alone.

What is the method used to test for hydrogen gas?

To test for hydrogen, a lit splint is placed at the mouth of the reaction vessel. The presence of hydrogen is confirmed when a distinctive 'squeaky pop' sound is heard.

What causes the 'squeaky pop' sound when testing for hydrogen?

The 'squeaky pop' sound is due to the combustion reaction of hydrogen in the presence of oxygen, producing water as the only product. This reaction causes a mini-explosion.

How do you test for oxygen gas?

To test for oxygen, a glowing splint is placed at the mouth of the reaction vessel. If the splint relights, oxygen is present.

Why should the splint be glowing, not lit, when testing for oxygen?

The splint should be glowing because a glowing splint, not a lit one, will relight in the presence of oxygen, indicating the gas is present.

What is the reason oxygen causes the glowing splint to relight?

Oxygen has a higher concentration in the reaction vessel compared to air, which contains only 21% oxygen. This increased concentration causes the glowing splint to relight.

How can carbon dioxide be tested in the laboratory?

Carbon dioxide can be tested by bubbling it through limewater, an aqueous solution of calcium hydroxide. Limewater turns milky in the presence of carbon dioxide due to the formation of calcium carbonate.

What happens when ammonia is tested with a lit splint or damp red litmus paper?

Ammonia extinguishes a lit splint and turns damp red litmus paper blue. In the presence of concentrated hydrochloric acid, a white smoke of ammonium chloride forms.

What does chlorine do to damp blue litmus paper?

Chlorine turns damp blue litmus paper red and eventually bleaches it to white, confirming its presence.

What are the key tests for identifying different gases, as mentioned in the lesson?

The key tests include: hydrogen causing a 'squeaky pop' when burned, oxygen relighting a glowing splint, carbon dioxide turning limewater milky, ammonia turning red litmus paper blue and forming white smoke with hydrochloric acid, and chlorine turning blue litmus paper red and bleaching it white.