Identification Of Common Gases
Overview
Four stoppered test tubes sit on the bench and not one of them carries a label. Three hold gases you cannot see at all; the fourth has a faint green tint if you catch it against white paper. There is no instrument in the room that will read them out for you. What you do have is a wooden splint, a strip of coloured paper, a bottle of cloudy-looking water and your own sense of smell used very carefully. Within about three minutes, every tube can be named.
That is the quiet promise of qualitative analysis: a handful of cheap, repeatable observations, each one designed so that a single gas gives a result nothing else gives. This lesson works through the four gases OxfordAQA expects you to identify, shows the reaction behind each observation rather than asking you to memorise a list, and deals with the two details that quietly cost marks every year: why the paper has to be damp, and why a limewater test left running too long can tell you the opposite of the truth.
Objectives
- A pop is heard when a lighted splint is placed near hydrogen gas.
- A glowing splint relights in a test tube of oxygen gas.
- Carbon dioxide turns limewater (calcium hydroxide solution) cloudy white.
- Chlorine has a characteristic sharp, choking smell. It also makes damp blue litmus paper turn red, and then bleaches it white.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Identification Of Common Gases. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which gas relights a glowing splint? A. hydrogen B. oxygen C. carbon dioxide D. chlorine Answer: B
- A colourless gas is bubbled through limewater and the limewater turns cloudy white. The gas is: A. chlorine B. hydrogen C. carbon dioxide D. oxygen Answer: C
- Damp blue litmus paper is held in a tube of gas. The paper turns red and is then bleached white. Which gas is in the tube? A. oxygen B. chlorine C. hydrogen D. carbon dioxide Answer: B
- Why must the litmus paper be damp when testing for chlorine? A. Damp paper is easier to hold in the tube. B. The water cools the gas so that it reacts more slowly. C. The chlorine must dissolve in the water and react with it to form acids. D. The water reacts with the chlorine to produce calcium carbonate. Answer: C
- A lighted splint is held at the mouth of a tube of gas and a squeaky pop is heard. Which gas is in the tube, and what is the product of the reaction? A. oxygen, and the product is carbon dioxide B. hydrogen, and the product is water C. hydrogen, and the product is hydrogen chloride D. chlorine, and the product is water Answer: B
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