Identification Of Ions And Gases (continued)
Overview
Faced with an unknown solution, a chemist can name the ions in it using a short list of simple, reliable tests. A few drops of sodium hydroxide, a wisp of ammonia, a flame and a damp piece of litmus paper are enough to identify a whole range of cations and gases by the colours they produce.
In this lesson you will learn the tests for aqueous cations using sodium hydroxide and ammonia solution, the flame-test colours of the common metal ions, and the tests for six important gases. These are high-value, frequently examined practical facts, and learning the exact colours is worth easy marks.
Objectives
- Describe tests using aqueous sodium hydroxide and aqueous ammonia to identify the aqueous cations: (a) aluminium, Al³⁺ (b) ammonium, NH₄⁺ (c) calcium, Ca²⁺ (d) chromium(III), Cr³⁺ (e) copper(II), Cu²⁺ (f) iron(II), Fe²⁺ (g) iron(III), Fe³⁺ (h) zinc, Zn²⁺.
- Describe tests to identify the gases: (a) ammonia, NH₃, using damp red litmus paper (b) carbon dioxide, CO₂, using limewater (c) chlorine, Cl₂, using damp litmus paper (d) hydrogen, H₂, using a lighted splint (e) oxygen, O₂, using a glowing splint (f) sulfur dioxide, SO₂, using acidified aqueous potassium manganate(VII).
- Describe the use of a flame test to identify the cations: (a) lithium, Li+ (b) sodium, Na+ (c) potassium, K+ (d) calcium, Ca2+ (e) barium, Ba2+ (f) copper(II), Cu2+.
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Lesson Evaluation
Congratulations on completing the lesson on Identification Of Ions And Gases (continued). 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 cation gives a light blue precipitate with sodium hydroxide that does NOT dissolve in excess? A. Aluminium B. Copper(II) C. Zinc D. Calcium Answer: B
- Which cation gives a precipitate that dissolves in excess ammonia to form a dark blue solution? A. Iron(III) B. Copper(II) C. Calcium D. Aluminium Answer: B
- What is the flame-test colour of a potassium ion? A. Yellow B. Red C. Lilac D. Light green Answer: C
- Which gas relights a glowing splint? A. Hydrogen B. Carbon dioxide C. Oxygen D. Ammonia Answer: C
- Which gas turns damp red litmus paper blue? A. Chlorine B. Carbon dioxide C. Sulfur dioxide D. Ammonia Answer: D
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