Lesson Note on Qualitative Analysis: Identification of Ions and Common Anions for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemical Analysis
Previous Lesson: Qualitative Analysis: Testing Ions and Oxidants.
Topic: QUANTITATIVE AND QUALITATIVE ANALYSIS
Subject Matter: Identification of ions (Fe2+, NH4+, Fe3+, Cu2+, Pb2+), identification of anions (chlorides, nitrates, sulphates, sulphide, bicarbonates, carbonates, sulphite)

Specific Objectives

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

Cognitive Domain:

• Define qualitative analysis and state its purpose.
• State the reagents and observations for identifying common cations (Fe2+, NH4+, Fe3+, Cu2+, Pb2+).
• State the reagents and observations for identifying common anions (chlorides, nitrates, sulphates, sulphide, bicarbonates, carbonates, sulphite).

Affective Domain:

• Appreciate the importance of qualitative analysis in chemistry.
• Show interest in performing practical tests for ion identification.

Psychomotor Domain:

• Perform simple tests to identify selected cations and anions.
• Accurately interpret the outcomes of qualitative tests.
• Handle laboratory apparatus and reagents safely during experiments.

Social Domain:

• Work collaboratively in groups to perform identification tests.
• Communicate observations and conclusions clearly with peers and the teacher.

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://waeconline.org.ng/e-learning/Chemistry/chem305.html
• https://chemistry.stackexchange.com/questions/qualitative-analysis-of-inorganic-salts

Instructional Materials

The teacher will teach this lesson with the aid of:

• Relevant salts containing Fe2+, NH4+, Fe3+, Cu2+, Pb2+ ions.
• Relevant salts containing chloride, nitrate, sulphate, sulphide, bicarbonate, carbonate, sulphite ions.
• Reagents: Sodium hydroxide solution, aqueous ammonia, dilute hydrochloric acid, barium chloride solution, silver nitrate solution, concentrated tetraoxosulphate(VI) acid, iron(II) tetraoxosulphate(VI) solution, magnesium sulphate solution, lead(II) acetate paper, acidified potassium tetraoxomanganate(VII), acidified potassium dichromate(VI), limewater.
• Test tubes, test tube rack, droppers, Bunsen burner.

Rationale for the Lesson

This lesson enables pupils to understand how to identify unknown chemical substances in the laboratory. It helps them develop practical skills in performing chemical tests and interpreting observations, which is important for everyday applications and further studies in chemistry.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of acids, bases, salts, chemical reactions, solubility rules, and safety precautions in the laboratory.

Lesson Content/Board Summary

QUALITATIVE ANALYSIS

Introduction to Qualitative Analysis

Qualitative analysis is a branch of chemistry that deals with the identification of the components (elements or compounds) present in a sample. It focuses on identifying the unknown substances rather than determining their quantities.

Identification of Cations

Cations are positively charged ions. Their presence is often identified by adding specific reagents and observing the formation of precipitates, colour changes, or gas evolution.

• Iron(II) ion (Fe2+)
  • Test with Sodium Hydroxide (NaOH) solution: Green precipitate formed, insoluble in excess NaOH.
  • Test with Aqueous Ammonia (NH3(aq)): Green precipitate formed, insoluble in excess NH3(aq).
• Iron(III) ion (Fe3+)
  • Test with Sodium Hydroxide (NaOH) solution: Reddish-brown precipitate formed, insoluble in excess NaOH.
  • Test with Aqueous Ammonia (NH3(aq)): Reddish-brown precipitate formed, insoluble in excess NH3(aq).
• Ammonium ion (NH4+)
  • Test with Sodium Hydroxide (NaOH) solution: Add NaOH to the sample and warm gently. A pungent gas (ammonia, NH3) is evolved, which turns damp red litmus paper blue.
• Copper(II) ion (Cu2+)
  • Test with Sodium Hydroxide (NaOH) solution: Pale blue precipitate formed, insoluble in excess NaOH.
  • Test with Aqueous Ammonia (NH3(aq)): Pale blue precipitate formed, soluble in excess NH3(aq) to give a deep blue solution.
• Lead(II) ion (Pb2+)
  • Test with Sodium Hydroxide (NaOH) solution: White precipitate formed, soluble in excess NaOH.
  • Test with Aqueous Ammonia (NH3(aq)): White precipitate formed, insoluble in excess NH3(aq).
  • Test with Dilute Hydrochloric Acid (HCl): White precipitate formed, which dissolves on heating and reappears on cooling.

Identification of Anions

Anions are negatively charged ions. Their identification involves tests that produce characteristic precipitates, gases, or colour changes.

• Chloride ion (Cl-)
  • Test: Add dilute nitric acid (HNO3) followed by silver nitrate solution (AgNO3). A white precipitate of silver chloride (AgCl) is formed, which is soluble in aqueous ammonia.
• Nitrate ion (NO3-) – Brown Ring Test
  • Test: To the solution, add freshly prepared iron(II) tetraoxosulphate(VI) solution (FeSO4). Carefully add concentrated tetraoxosulphate(VI) acid (H2SO4) down the side of the test tube. A brown ring forms at the junction of the two liquids.
• Sulphate ion (SO42-)
  • Test: Add dilute hydrochloric acid (HCl) followed by barium chloride solution (BaCl2). A white precipitate of barium sulphate (BaSO4) is formed, which is insoluble in excess dilute HCl.
• Sulphide ion (S2-)
  • Test: Add dilute hydrochloric acid (HCl). A gas with a characteristic rotten egg smell (hydrogen sulphide, H2S) is evolved, which turns lead(II) acetate paper black.
• Carbonate ion (CO32-) and Bicarbonate ion (HCO3-)
  • General Test: Add dilute acid (e.g., HCl). Effervescence occurs, and the gas evolved (carbon dioxide, CO2) turns limewater milky.
  • Distinguishing Test:
    • Add magnesium sulphate solution (MgSO4) to the cold sample. Carbonates give a white precipitate immediately, while bicarbonates do not.
    • Upon heating, bicarbonates decompose to give CO2 which turns limewater milky, while carbonates do not react further.
• Sulphite ion (SO32-)
  • Test: Add dilute hydrochloric acid (HCl). A gas (sulphur dioxide, SO2) is evolved, which turns acidified potassium tetraoxomanganate(VII) (KMnO4) solution from purple to colourless, or acidified potassium dichromate(VI) (K2Cr2O7) solution from orange to green.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall what they know about identifying substances in daily life, e.g., identifying different types of food by taste or smell. The teacher then introduces the topic of qualitative analysis in chemistry.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils connect prior knowledge to the new topic and understand the relevance of identification.

Step 2: Explanation of Qualitative Analysis

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines qualitative analysis and explains its purpose in chemistry, emphasizing its role in identifying unknown components of a sample. The teacher also highlights the difference between qualitative and quantitative analysis.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and purpose of qualitative analysis.

Step 3: Cation Identification (Fe2+, Fe3+, NH4+)

Time: 8 minutes
Teaching Skill: Demonstration/Practical Activity
Teacher’s Activity: The teacher demonstrates the tests for Fe2+, Fe3+, and NH4+ ions using appropriate reagents (NaOH, NH3(aq), heating). The teacher guides pupils to observe the changes carefully and record their observations.
Pupils’ Activity: Pupils observe the demonstrations, record the reagents and observations, and ask questions.
Learning Point: Pupils learn the specific tests and characteristic observations for these cations.

Step 4: Cation Identification (Cu2+, Pb2+)

Time: 7 minutes
Teaching Skill: Demonstration/Practical Activity
Teacher’s Activity: The teacher continues by demonstrating the tests for Cu2+ and Pb2+ ions, including the use of NaOH, NH3(aq), and dilute HCl where applicable. The teacher emphasizes the solubility in excess reagents.
Pupils’ Activity: Pupils watch the demonstrations, note the observations, and understand the distinguishing characteristics of these ions.
Learning Point: Pupils consolidate their knowledge of cation identification tests and observations.

Step 5: Anion Identification (Chlorides, Nitrates, Sulphates)

Time: 7 minutes
Teaching Skill: Demonstration/Practical Activity
Teacher’s Activity: The teacher demonstrates the tests for chloride (AgNO3/HNO3), nitrate (brown ring test), and sulphate (BaCl2/HCl) ions, guiding pupils through each step and observation.
Pupils’ Activity: Pupils observe the demonstrations, record the procedures and results, and pay attention to specific details like the brown ring formation.
Learning Point: Pupils learn the tests for selected common anions.

Step 6: Anion Identification (Sulphide, Bicarbonates, Carbonates, Sulphite)

Time: 7 minutes
Teaching Skill: Demonstration/Practical Activity
Teacher’s Activity: The teacher demonstrates the tests for sulphide (HCl/lead acetate paper), carbonate/bicarbonate (dilute acid/limewater, MgSO4), and sulphite (dilute HCl/KMnO4 or K2Cr2O7) ions, highlighting distinguishing features.
Pupils’ Activity: Pupils observe the demonstrations, take notes on the reagents, observations, and confirming tests.
Learning Point: Pupils understand how to identify these anions and distinguish between similar ones.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is qualitative analysis?
2. State the observation when sodium hydroxide solution is added to a solution containing Fe2+ ions.
3. How would you distinguish between a solution containing Cu2+ ions and one containing Pb2+ ions using aqueous ammonia?
4. Describe the test for the presence of chloride ions in a solution.
5. Outline the steps for performing the brown ring test for nitrate ions.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of accurate observation and interpretation in qualitative analysis. The teacher assigns homework, asking pupils to write down all the tests and observations discussed for both cations and anions.
Pupils’ Activity: Pupils listen to the summary, ask any final questions, and copy the homework assignment.
Learning Point: Pupils consolidate their learning and receive further practice.

Lesson Keywords

• Qualitative Analysis – The branch of chemistry concerned with the identification of substances present in a sample.
• Cation – A positively charged ion.
• Anion – A negatively charged ion.
• Precipitate – An insoluble solid that separates from a solution.
• Reagent – A substance used to cause a chemical reaction, especially to detect or measure another substance.

Differentiation

For pupils who grasp concepts quickly, they can be encouraged to research the chemical equations for the reactions involved in the identification tests. For those needing more support, the teacher can provide simplified charts or mnemonics to help remember the tests and observations, and offer additional guided practice with the instructional materials.

Note for teachers using this lesson plan

Ensure all reagents are properly labeled and safely handled. Emphasize laboratory safety rules throughout the practical demonstrations. Encourage pupils to ask questions and participate actively. If practical demonstrations are not feasible, use visual aids like videos or detailed diagrams to illustrate the tests and observations.