Gas tests for IGCSE and O Level Chemistry

Summary

This chemistry experiment demonstrates a series of tests to identify different gases. First, ammonia is tested by reacting ammonium chloride with sodium hydroxide, producing an alkaline gas that turns red litmus paper blue. Carbon dioxide is produced by reacting calcium carbonate with hydrochloric acid, turning lime water cloudy. Chlorine gas is identified by bleaching blue litmus paper, while hydrogen gas is detected with a pop sound when reacted with zinc powder. Oxygen is tested with a glowing splint, and sulfur dioxide is identified by decolorizing potassium manganate solution. The experiment showcases key reactions to identify common gases in the lab.

Takeaways

• 😀 Ammonia gas is tested by reacting ammonium chloride with sodium hydroxide and heating the mixture. The gas turns red litmus paper blue and has a pungent smell.
• 😀 Carbon dioxide gas is produced by reacting a carbonate (e.g., calcium carbonate) with hydrochloric acid. The gas turns lime water cloudy, confirming its presence.
• 😀 Chlorine gas is generated by reacting bleach with hydrochloric acid. It bleaches damp blue litmus paper and has a distinct swimming pool smell.
• 😀 Hydrogen gas is produced by reacting zinc with hydrochloric acid. It creates a 'pop' sound when introduced to a lighted splint.
• 😀 Oxygen gas is produced by decomposing hydrogen peroxide with the help of a manganese dioxide catalyst. It reignites a glowing splint.
• 😀 Sulfur dioxide gas is produced by reacting sodium sulfide with hydrochloric acid. It decolorizes potassium manganate (VII) and has a choking smell.
• 😀 Each experiment uses a specific chemical reaction to generate the gas being tested, relying on their distinct properties for identification.
• 😀 Damp litmus paper is used in several tests to identify whether a gas is acidic or alkaline (e.g., ammonia turns red litmus paper blue).
• 😀 Lime water is used to confirm the presence of carbon dioxide, as it turns cloudy due to the formation of calcium carbonate.
• 😀 The production of gases such as hydrogen, oxygen, and ammonia can be confirmed by physical tests like popping sounds, glowing splints, or color changes in litmus paper.

Q & A

What is the purpose of Experiment 18.1?

The purpose of Experiment 18.1 is to test for the presence of various gases, including ammonia, carbon dioxide, chlorine, hydrogen, oxygen, and sulfur dioxide, by performing specific chemical reactions and observing their characteristics.

How is ammonia gas produced in the experiment?

Ammonia gas is produced by reacting ammonium chloride with sodium hydroxide and gently heating the mixture. The gas is then tested using damp red litmus paper, which turns blue, indicating its alkalinity.

What visual cue indicates the presence of ammonia gas?

The presence of ammonia gas is indicated when damp red litmus paper turns blue, confirming the gas is alkaline. Additionally, ammonia has a pungent smell.

How is carbon dioxide gas produced in the experiment?

Carbon dioxide is produced by reacting calcium carbonate with hydrochloric acid, which generates the gas. The gas is then passed through limewater, which turns cloudy, confirming the presence of carbon dioxide.

What is the significance of limewater turning cloudy in the carbon dioxide test?

When carbon dioxide is bubbled through limewater (calcium hydroxide solution), it reacts to form calcium carbonate, a white solid. This causes the limewater to turn cloudy, indicating the presence of carbon dioxide.

How do you test for chlorine gas in this experiment?

To test for chlorine gas, you use damp blue litmus paper, which turns white upon exposure to chlorine gas. Chlorine also has a distinct swimming pool-like smell.

What reaction is used to test for hydrogen gas?

Hydrogen gas is produced by reacting zinc powder with hydrochloric acid. The presence of hydrogen is confirmed when a lighted splint produces a characteristic 'pop' sound upon contact with the gas.

What does the 'pop' sound indicate in the hydrogen test?

The 'pop' sound indicates the presence of hydrogen gas. This occurs when hydrogen reacts with oxygen from the air to produce water, causing a rapid combustion that produces the sound.

How is oxygen gas produced in this experiment?

Oxygen gas is produced by decomposing hydrogen peroxide using a catalyst, manganese dioxide. The reaction occurs at room temperature and pressure but is sped up with the catalyst.

How is sulfur dioxide gas tested in the experiment?

Sulfur dioxide gas is produced by reacting sodium sulfide with hydrochloric acid. The gas is tested by passing it over acidified potassium manganate(VII) paper, which loses its purple color in the presence of sulfur dioxide.