Lesson Note on Qualitative Analysis: Gas Tests and Food Tests for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 11
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Quantitative and Qualitative Analysis
Previous Lesson: Qualitative Analysis: Identification of Ions and Common Anions.
Topic: QUANTITATIVE AND QUALITATIVE ANALYSIS
Subject Matter: Test for gases (hydrogen, NH3, HCl, NO2, oxygen, CO2, Cl2 bleaching action), identification of food substances (fats and oils, simple sugar, proteins, starch)

Specific Objectives

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

Cognitive Domain:

• State the reagents used to test for various gases.
• Describe the observations for identifying different food substances.

Affective Domain:

• Appreciate the importance of qualitative analysis in chemistry.
• Value accuracy in performing chemical tests.

Psychomotor Domain:

• Carry out simple laboratory tests to identify common gases.
• Perform tests to identify starch, simple sugars, proteins, and fats/oils in food samples.

Social Domain:

• Collaborate effectively during practical sessions.
• Communicate observations clearly and concisely.

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

Instructional Materials

The teacher will teach this lesson with the aid of:

• Test tubes and test tube rack
• Bunsen burner and tripod stand
• Lighted and glowing splints
• Red and blue litmus papers
• Lime water (calcium hydroxide solution)
• Iodine solution
• Biuret reagent (or NaOH and CuSO4 solutions)
• Ethanol
• Distilled water
• Samples of starch, sugar, protein (e.g., egg albumin), cooking oil
• Dilute hydrochloric acid
• Ammonia solution
• Potassium permanganate solution (for NO2 test)

Rationale for the Lesson

This lesson helps pupils understand how to identify unknown substances, which is a fundamental skill in chemistry. It enables them to apply practical knowledge to distinguish between different gases and important food components, connecting classroom learning to real-world applications like food science and environmental monitoring.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of the properties of matter, chemical reactions, and laboratory safety procedures.

Lesson Content/Board Summary

QUANTITATIVE AND QUALITATIVE ANALYSIS

Introduction to Qualitative Analysis

Qualitative analysis is a branch of chemistry that deals with the identification of elements or compounds present in a sample. It focuses on determining “what is present” rather than “how much is present.”

Tests for Common Gases

• Hydrogen (H₂)

  Test: Bring a lighted splint to the mouth of the test tube containing the gas.

  Observation: The splint extinguishes with a ‘pop’ sound.

• Oxygen (O₂)

  Test: Insert a glowing splint into the test tube containing the gas.

  Observation: The glowing splint rekindles.

• Carbon Dioxide (CO₂)

  Test: Bubble the gas through lime water (calcium hydroxide solution).

  Observation: The lime water turns milky (forms a white precipitate of CaCO₃).

• Ammonia (NH₃)

  Test 1: Bring a moist red litmus paper to the mouth of the test tube containing the gas.

  Observation 1: The red litmus paper turns blue.

  Test 2: Bring a glass rod dipped in concentrated HCl to the mouth of the test tube.

  Observation 2: Dense white fumes (of NH₄Cl) are produced.

• Hydrogen Chloride (HCl gas)

  Test 1: Bring a moist blue litmus paper to the mouth of the test tube containing the gas.

  Observation 1: The blue litmus paper turns red.

  Test 2: Bring a glass rod dipped in concentrated ammonia solution to the mouth of the test tube.

  Observation 2: Dense white fumes (of NH₄Cl) are produced.

• Nitrogen Dioxide (NO₂)

  Test: Observe the colour of the gas.

  Observation: The gas is reddish-brown.

  Test 2: Introduce moist blue litmus paper.

  Observation 2: Blue litmus paper turns red.

• Chlorine (Cl₂)

  Test 1: Observe the colour of the gas.

  Observation 1: The gas is greenish-yellow.

  Test 2: Introduce moist blue litmus paper.

  Observation 2: The blue litmus paper turns red and then bleaches (turns white).

Identification Tests for Food Substances

• Starch

  Test: Add a few drops of iodine solution to the food sample.

  Observation: The solution turns blue-black.

• Simple Sugars (Reducing Sugars like Glucose)

  Test: Add Benedict’s solution to the food sample and heat gently in a water bath.

  Observation: The solution changes colour from blue to green, yellow, orange, or brick-red precipitate, depending on the concentration of sugar.

• Proteins

  Test (Biuret Test): Add equal volumes of dilute sodium hydroxide solution and dilute copper(II) sulphate solution to the food sample.

  Observation: A violet or purple colour develops.

• Fats and Oils

  Test 1 (Translucency Test): Rub the food sample on a piece of filter paper.

  Observation 1: A translucent spot (oil stain) appears on the paper.

  Test 2 (Emulsion Test): Dissolve the food sample in ethanol, then pour the ethanol solution into water.

  Observation 2: A milky white emulsion is formed.

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 introduces the topic by asking them what they understand by identifying unknown substances in the laboratory.
Pupils’ Activity: Pupils respond to the teacher’s questions and state their ideas about identifying substances.
Learning Point: Pupils are introduced to the concept of qualitative analysis.

Step 2: Explanation of Qualitative Analysis

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines qualitative analysis and explains its importance in chemistry, particularly in identifying gases and components of food substances.
Pupils’ Activity: Pupils listen attentively and take notes on the definition and importance of qualitative analysis.
Learning Point: Pupils understand the meaning and relevance of qualitative analysis.

Step 3: Test for Gases (Part 1)

Time: 10 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher demonstrates and guides pupils to perform tests for hydrogen, oxygen, and carbon dioxide gases, ensuring safety and proper observation. The teacher records observations on the board.
Pupils’ Activity: Pupils observe the demonstrations, participate in performing the tests carefully, and record their observations in their notebooks.
Learning Point: Pupils learn how to identify hydrogen, oxygen, and carbon dioxide gases.

Step 4: Test for Gases (Part 2)

Time: 7 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher continues by demonstrating and guiding pupils to perform tests for ammonia, hydrogen chloride, nitrogen dioxide, and chlorine gases. The teacher emphasizes safety precautions.
Pupils’ Activity: Pupils observe, participate in the tests, and record the characteristic observations for each gas.
Learning Point: Pupils learn how to identify ammonia, hydrogen chloride, nitrogen dioxide, and chlorine gases.

Step 5: Introduction to Food Substance Tests

Time: 3 minutes
Teaching Skill: Explanation/Connection
Teacher’s Activity: The teacher introduces the concept of identifying food substances, explaining why it is important to know what nutrients are present in different foods.
Pupils’ Activity: Pupils listen and contribute ideas on why food tests are important.
Learning Point: Pupils understand the significance of identifying components in food.

Step 6: Identification of Food Substances

Time: 10 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher demonstrates and guides pupils to perform tests for starch, simple sugars, proteins, and fats/oils using appropriate reagents. The teacher records observations on the board.
Pupils’ Activity: Pupils observe the demonstrations, carefully perform the tests, and record their observations and conclusions.
Learning Point: Pupils learn to identify various food substances using chemical tests.

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. How would you test for the presence of hydrogen gas?
2. State the observation when carbon dioxide is bubbled through lime water.
3. Describe the test for starch in a food sample.
4. What is the expected result when testing for protein using the Biuret test?

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/Assignment
Teacher’s Activity: The teacher summarizes the key learning points about the tests for gases and food substances and assigns homework: “List two practical applications of qualitative analysis in everyday life.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: The lesson is concluded with a recap and a take-home assignment.

Lesson Keywords

• Qualitative analysis – Identification of substances in a sample.
• Hydrogen – Gas that extinguishes a lighted splint with a ‘pop’ sound.
• Oxygen – Gas that rekindles a glowing splint.
• Carbon Dioxide – Gas that turns lime water milky.
• Ammonia – Alkaline gas that turns moist red litmus blue and forms white fumes with HCl.
• Chlorine – Greenish-yellow gas that bleaches moist litmus paper.
• Starch – Food substance that turns blue-black with iodine solution.
• Simple sugars – Food substance that gives a colour change with Benedict’s solution upon heating.
• Proteins – Food substance that gives a violet colour with Biuret reagent.
• Fats and oils – Food substance that forms a translucent spot on paper or a white emulsion with ethanol and water.

Differentiation

For pupils who grasp the concepts quickly, the teacher can challenge them to explain the chemical reactions behind the observations. For those who need more support, the teacher will provide simplified instructions, more direct guidance during practicals, and repeat demonstrations as necessary.

Note for teachers using this lesson plan

Ensure all reagents and equipment are readily available and in good working condition before the lesson. Emphasize safety precautions, especially when handling gases and using a Bunsen burner. Encourage active participation from all pupils during the practical sessions and allow them to record their observations accurately.