Lesson Note on Qualitative Analysis: Testing Ions and Oxidants for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 9
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Analytical Chemistry
Previous Lesson: Quantitative and Qualitative Analysis: Titrations and Redox Titrations.
Topic: QUANTITATIVE AND QUALITATIVE ANALYSIS
Subject Matter: Test for oxidants and reductants, analysis of substances and test for cations and anions (Fe2+, Cu2+, NH4+, SO4 2-, SO3 2-)

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define qualitative and quantitative analysis.
• State the tests for specific cations (Fe2+, Cu2+, NH4+).
• Identify the tests for specific anions (SO4 2-, SO3 2-).
• Explain how to test for oxidants and reductants.

Affective Domain:

• Appreciate the importance of qualitative analysis in identifying unknown substances.
• Develop an interest in practical chemistry and analytical procedures.

Psychomotor Domain:

• Perform simple chemical tests to identify Fe2+, Cu2+, NH4+, SO4 2-, and SO3 2- ions.
• Record observations accurately during chemical tests.
• Handle chemical reagents and apparatus safely.

Social Domain:

• Collaborate with peers during practical demonstrations and discussions.
• Communicate their observations and inferences clearly.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio.
• https://chemistry.stackexchange.com/
• https://www.chemguide.co.uk/

Instructional Materials

The teacher will teach this lesson with the aid of:

• Test tubes and test tube rack
• Droppers
• Bunsen burner
• Samples of salts containing Fe2+, Cu2+, NH4+, SO4 2-, SO3 2- ions
• Reagents: Dilute NaOH, aqueous ammonia, dilute HCl, BaCl2 solution, acidified potassium permanganate(VII) solution, acidified potassium dichromate(VI) solution, red litmus paper.

Rationale for the Lesson

This lesson helps pupils understand how to identify unknown chemical substances through systematic tests. This skill is important for further studies in chemistry and for various industrial applications where knowing the composition of materials is essential.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of ions, chemical reactions, acids, bases, and redox reactions from previous lessons.

Lesson Content/Board Summary

QUANTITATIVE AND QUALITATIVE ANALYSIS

Introduction to Qualitative and Quantitative Analysis

Qualitative Analysis involves identifying the components (elements or compounds) present in a sample. It tells us “what” is in the sample.

Quantitative Analysis involves determining the amount or concentration of each component present in a sample. It tells us “how much” of each component is in the sample.

Tests for Cations

• Iron(II) ion (Fe2+)
  • With dilute Sodium Hydroxide (NaOH) solution: A dirty green precipitate forms, which is insoluble in excess NaOH.
  • With aqueous Ammonia (NH3(aq)) solution: A dirty green precipitate forms, which is insoluble in excess NH3(aq).
• Copper(II) ion (Cu2+)
  • With dilute Sodium Hydroxide (NaOH) solution: A light blue precipitate forms, which is insoluble in excess NaOH.
  • With aqueous Ammonia (NH3(aq)) solution: A light blue precipitate forms, which dissolves in excess NH3(aq) to form a deep blue solution.
• Ammonium ion (NH4+)
  • With dilute Sodium Hydroxide (NaOH) solution (warmed): A colourless gas with a pungent smell is evolved. This gas turns damp red litmus paper blue.

Tests for Anions

• Sulphate ion (SO4 2-)
  • Procedure: Add dilute Hydrochloric Acid (HCl), then add Barium Chloride (BaCl2) solution.
  • Observation: A white precipitate (Barium Sulphate, BaSO4) forms, which is insoluble in excess dilute HCl.
• Sulphite ion (SO3 2-)
  • Procedure: Add dilute Hydrochloric Acid (HCl).
  • Observation: A colourless gas (Sulphur Dioxide, SO2) with a pungent smell is evolved. This gas turns acidified Potassium Dichromate(VI) solution from orange to green.
  • Alternative Test: Add Barium Chloride (BaCl2) solution, then add dilute Hydrochloric Acid (HCl).
  • Observation: A white precipitate forms, which is soluble in excess dilute HCl.

Tests for Oxidants and Reductants

Oxidants are substances that gain electrons and cause the oxidation of other substances. They are themselves reduced.

Reductants are substances that lose electrons and cause the reduction of other substances. They are themselves oxidized.

• Test for Oxidants:
  • Oxidants typically oxidize iodide ions (I-) to iodine (I2).
  • Procedure: Add a solution of Potassium Iodide (KI) to the sample.
  • Observation: A brown solution forms (due to I2), which turns blue-black with starch solution.
• Test for Reductants:
  • Reductants typically reduce acidified Potassium Permanganate(VII) solution (KMnO4) from purple to colourless.
  • Procedure: Add acidified Potassium Permanganate(VII) solution to the sample.
  • Observation: The purple colour of the KMnO4 solution disappears (decolorized).

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids, Practical/Experimental

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks questions about identifying unknown substances in daily life, such as identifying a type of food by its taste or smell, relating it to chemical identification.
Pupils’ Activity: Pupils respond to the teacher’s questions, sharing their ideas.
Learning Point: Pupils are introduced to the concept of identification and analysis.

Step 2: Definition of Qualitative and Quantitative Analysis

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines qualitative and quantitative analysis, explaining the difference between identifying “what” is present and “how much” is present.
Pupils’ Activity: Pupils listen attentively and copy the definitions into their notebooks.
Learning Point: Pupils understand the fundamental concepts of qualitative and quantitative analysis.

Step 3: Tests for Cations (Fe2+, Cu2+, NH4+)

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher demonstrates the tests for Fe2+, Cu2+, and NH4+ ions using relevant reagents. The teacher guides pupils to observe the colour changes and precipitate formations carefully.
Pupils’ Activity: Pupils observe the demonstrations, record their observations, and copy the test procedures and results into their notebooks.
Learning Point: Pupils learn the specific tests and expected observations for identifying Fe2+, Cu2+, and NH4+ ions.

Step 4: Tests for Anions (SO4 2-, SO3 2-)

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher demonstrates the tests for SO4 2- and SO3 2- ions, emphasizing the steps and characteristic observations like gas evolution or precipitate formation and solubility.
Pupils’ Activity: Pupils observe the demonstrations, record their observations, and copy the test procedures and results into their notebooks.
Learning Point: Pupils learn the specific tests and expected observations for identifying SO4 2- and SO3 3- ions.

Step 5: Tests for Oxidants and Reductants

Time: 5 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains what oxidants and reductants are and demonstrates simple tests for their identification using acidified potassium permanganate(VII) or potassium iodide.
Pupils’ Activity: Pupils pay attention, ask questions for clarification, and note down the key points of the tests.
Learning Point: Pupils understand how to identify oxidants and reductants based on their chemical properties.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Differentiate between qualitative and quantitative analysis.
2. State the observation when dilute NaOH is added to a solution containing Fe2+ ions.
3. Describe the test for the presence of SO3 2- ions.
4. How would you test a substance to determine if it is a reductant?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 5 minutes
Teaching Skill: Summarizing
Teacher’s Activity: The teacher summarizes the key learning points, emphasizing the importance of accurate observation and inference in qualitative analysis. The teacher gives homework.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding of the topic and prepare for future learning.

Lesson Keywords

• Qualitative Analysis – Identifying the components of a substance.
• Quantitative Analysis – Determining the amount of each component in a substance.
• Cation – A positively charged ion.
• Anion – A negatively charged ion.
• Oxidant – A substance that causes oxidation by gaining electrons.
• Reductant – A substance that causes reduction by losing electrons.
• Precipitate – An insoluble solid formed from a solution.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional unknown samples for them to identify using the learned tests. For pupils needing more support, the teacher can provide simplified flowcharts of the tests and offer more guided practice during demonstrations.

Note for teachers using this lesson plan

Ensure all reagents are properly labeled and pupils are instructed on safety precautions, especially when handling acids, bases, and using the Bunsen burner. Emphasize the importance of clear observations and logical inferences. Practical demonstrations are crucial for this topic; ensure all necessary materials are available and in good working condition before the lesson.