Chemical Tests
Overview
How do you prove that the gas bubbling out of a reaction is hydrogen and not carbon dioxide? How can you tell whether a white powder contains copper ions or iron ions? Chemical tests give you a definitive answer, and the Edexcel specification requires you to know a precise toolkit of tests for gases, cations and anions.
In this lesson you will learn how to identify five common gases, carry out flame tests for metal cations, detect specific ions using reagents, and confirm whether a liquid is pure water. These tests appear regularly on both papers.
Objectives
- describe tests for these gases: - hydrogen - oxygen - carbon dioxide - ammonia - chlorine.
- describe how to carry out a flame test
- know the colours formed in flame tests for these cations:
- 2.48 - Li+ is red - Na+ is yellow - K+ is lilac - Ca2+ is orange-red - Cu2+ is blue-green. describe tests for these cations: - NH4+ using sodium hydroxide solution and identifying the gas evolved - Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution. describe tests for these anions: - Cl-, Br- and I- using acidified silver nitrate solution - SO42- using acidified barium chloride solution - CO32- using hydrochloric acid and identifying the gas evolved.
- describe a test for the presence of water using anhydrous copper(II) sulfate
- describe a physical test to show whether a sample of water is pure
Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Chemical Tests. 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) Carbon dioxide C) Oxygen D) Ammonia Answer: C
- A flame test produces an orange-red colour. Which cation is present? A) Lithium B) Sodium C) Calcium D) Copper Answer: C
- Adding sodium hydroxide to a solution produces a green precipitate. The cation present is: A) Cu2+ B) Fe2+ C) Fe3+ D) Na+ Answer: B
- Anhydrous copper(II) sulfate is used to test for: A) Carbon dioxide B) Oxygen C) Water D) Chlorine Answer: C
- A white precipitate with acidified silver nitrate indicates the presence of: A) Bromide ions B) Iodide ions C) Sulfate ions D) Chloride ions Answer: D
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
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