Testing For Hydrogen, Oxygen, Carbon Dioxide & Chlorine | Matter | Chemistry | FuseSchool

Summary

This lesson teaches methods to identify common gases through laboratory testing. Hydrogen is confirmed by its squeaky pop sound when burned, indicating a combustion reaction with oxygen. Oxygen relights a glowing splint due to its higher concentration. Carbon dioxide extinguishes a lit splint and turns lime water milky, forming calcium carbonate. Ammonia turns damp red litmus paper blue and forms white ammonium chloride smoke with hydrochloric acid. Chlorine bleaches blue litmus paper red and white. These tests help distinguish gases that are otherwise colorless and odorless.

Takeaways

• 🔍 Gases like hydrogen, oxygen, carbon dioxide, ammonia, and chlorine cannot be identified by appearance alone due to their colorless and odorless nature.
• 🔥 To test for hydrogen, place a lit splint at the mouth of the reaction vessel to hear a 'squeaky pop', indicating its presence through combustion.
• 🌪️ A glowing splint will reignite in the presence of oxygen, which is a distinctive test for oxygen's presence in a reaction vessel.
• 💥 The 'squeaky pop' of hydrogen is due to a mini explosion caused by its high flammability and the combustion reaction with oxygen.
• 🌀 Carbon dioxide extinguishes a lit splint, but a more accurate test involves bubbling it through lime water, which turns milky due to calcium carbonate formation.
• 🌊 Ammonia extinguishes a lit splint and turns damp red litmus paper blue, indicating its presence through a chemical reaction.
• 🌫️ In the presence of concentrated hydrochloric acid, ammonia forms a white smoke of ammonium chloride, confirming its presence.
• 🔴 Chlorine turns damp blue litmus paper red and eventually bleaches it to white, a unique test for chlorine's presence.
• 🧪 Testing for gases in the laboratory is crucial because it is nearly impossible to determine a gas's identity by its appearance alone.
• 🌬️ The concentration of oxygen in a reaction vessel is higher than in air (21%), which is why a glowing splint relights in its presence.
• 📝 In conclusion, each gas has a unique test: hydrogen burns with a pop, oxygen reignites a glowing splint, carbon dioxide turns lime water milky, ammonia turns red litmus paper blue and forms ammonium chloride smoke, and chlorine bleaches blue litmus paper.

Q & A

Why is it difficult to identify a gas by its appearance alone?

It is difficult because many gases, like hydrogen, oxygen, and carbon dioxide, are colorless and odorless, making them indistinguishable by sight or smell.

How can you confirm the presence of hydrogen in a reaction vessel?

Place a lit splint at the mouth of the reaction vessel; a distinctive squeaky pop sound indicates the presence of hydrogen due to its combustion reaction with oxygen.

What property of hydrogen causes the squeaky pop sound when it burns?

Hydrogen is highly flammable, and the pop sound is a result of a mini explosion caused by its rapid combustion in the presence of oxygen.

How do you test for the presence of oxygen in a reaction vessel?

Place a glowing splint at the mouth of the reaction vessel; the splint will reignite in the presence of oxygen.

Why does a glowing splint reignite in the presence of oxygen?

The glowing splint relights because the concentration of oxygen in the reaction vessel is higher than in air, which contains only 21% oxygen.

How can you differentiate between carbon dioxide and ammonia when both extinguish a lit splint?

Bubble the gas through lime water (calcium hydroxide solution); carbon dioxide will turn the lime water milky due to the formation of calcium carbonate.

What happens when carbon dioxide is bubbled through lime water?

Lime water turns milky in the presence of carbon dioxide because of the formation of calcium carbonate, which is a sign of carbon dioxide.

How does ammonia affect a damp red litmus paper?

Ammonia turns damp red litmus paper blue, indicating its basic nature.

What reaction occurs when ammonia is exposed to concentrated hydrochloric acid?

In the presence of concentrated hydrochloric acid, ammonia forms a white smoke of ammonium chloride, confirming its presence.

How can you test for the presence of chlorine gas?

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

What is the final conclusion of the lesson regarding the testing of different gases?

The lesson concludes that hydrogen burns with a squeaky pop, oxygen relights a glowing splint, carbon dioxide turns lime water milky, ammonia turns damp red litmus paper blue and forms white smoke of ammonium chloride with concentrated hydrochloric acid, and chlorine turns damp blue litmus paper red and bleaches it to white.