Class: Senior Secondary School 2 (SS2 / SSS2)
Term: Second Term
Week: 9
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry of Non-metals
Previous Lesson: Nitrogen: Meaning, Group Properties and Laboratory Preparation.
Topic: NITROGEN
Subject Matter: Industrial preparation of nitrogen from liquid air, properties of nitrogen

Specific Objectives

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

Cognitive Domain:

Explain the industrial preparation of nitrogen from liquid air.
State the physical and chemical properties of nitrogen.
Explain why nitrogen is generally unreactive.

Affective Domain:

Appreciate the industrial importance of nitrogen.
Show interest in the study of atmospheric gases.

Psychomotor Domain:

Draw appropriate diagrams for the laboratory preparation of nitrogen.
List the steps involved in the fractional distillation of liquid air.

Work collaboratively to discuss the properties of nitrogen.

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://www.britannica.com/science/nitrogen
https://www.thoughtco.com/nitrogen-facts-p2-606622

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts tabulating nitrogen group properties
Charts showing laboratory preparation of nitrogen
Diagrams of the nitrogen cycle
Periodic table
Whiteboard and markers

Rationale for the Lesson

This lesson helps pupils understand how nitrogen, a vital component of the atmosphere, is prepared on a large scale for industrial uses. It enables them to grasp the fundamental properties of nitrogen, which are essential for understanding its role in various chemical processes and its application in daily life.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of elements, mixtures (especially air), the concept of atmospheric gases, and basic principles of separation techniques like distillation.

Lesson Content/Board Summary

NITROGEN

Industrial Preparation of Nitrogen from Liquid Air

Nitrogen is prepared industrially from liquid air using the process of fractional distillation. Air is a mixture of gases, primarily nitrogen (approx. 78%) and oxygen (approx. 21%), which have different boiling points.

The steps involved in the industrial preparation are:

Filtration: Air is first filtered to remove dust particles.
Compression and Cooling: The filtered air is compressed to a high pressure and then cooled to a low temperature. This process removes carbon dioxide and water vapour, which freeze out.
Liquefaction: The purified air is then allowed to expand rapidly, which causes further cooling and liquefaction.
Fractional Distillation: The liquid air, primarily a mixture of liquid nitrogen and liquid oxygen, is then fed into a fractional distillation column. Due to their different boiling points, they separate:
- Liquid nitrogen has a lower boiling point (-196 °C) and boils off first, collected at the top of the column.
- Liquid oxygen has a higher boiling point (-183 °C) and remains in the liquid state, collected at the bottom.

Properties of Nitrogen

Nitrogen is a key element with distinct physical and chemical characteristics.

Physical Properties of Nitrogen

State: It is a colourless, odourless, and tasteless gas at room temperature.
Density: It is slightly less dense than air.
Solubility: It is sparingly soluble in water.
Boiling Point: -196 °C
Melting Point: -210 °C

Chemical Properties of Nitrogen

Nitrogen is generally unreactive at room temperature due to the strong triple covalent bond between its two atoms (N≡N).

Unreactivity: It does not burn or support combustion. It is unreactive with most substances under normal conditions.
Reaction with Active Metals: At high temperatures, nitrogen can react with very active metals (e.g., lithium, magnesium) to form nitrides.
Example: 6Li(s) + N₂(g) → 2Li₃N(s)
Reaction with Oxygen: At very high temperatures, such as during lightning discharges or in internal combustion engines, nitrogen reacts with oxygen to form oxides of nitrogen.
Example: N₂(g) + O₂(g) → 2NO(g)

Reason for Unreactivity

The nitrogen molecule (N₂) contains a very strong triple covalent bond (N≡N). A large amount of energy is required to break this bond, making nitrogen very stable and generally unreactive under normal conditions. It requires high temperatures or pressures to participate in chemical reactions.

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 the major components of air and their approximate percentages. The teacher also asks pupils if they know how individual gases from air can be obtained.
Pupils’ Activity: Pupils respond by mentioning nitrogen and oxygen as major components of air and state their percentages. They may suggest methods like distillation.
Learning Point: Pupils recall prior knowledge of air composition and separation techniques.

Step 2: Industrial Preparation of Nitrogen from Liquid Air

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the industrial process of obtaining nitrogen from liquid air, emphasizing fractional distillation. The teacher uses diagrams or charts to illustrate the process, explaining each stage from filtration to the collection of nitrogen.
Pupils’ Activity: Pupils listen attentively, observe the diagrams, and ask questions for clarification regarding the process and equipment used.
Learning Point: Pupils understand the principles and steps involved in the industrial preparation of nitrogen.

Step 3: Discussion on Fractional Distillation Details

Time: 8 minutes
Teaching Skill: Explaining/Questioning
Teacher’s Activity: The teacher elaborates on the concept of fractional distillation as applied to liquid air, highlighting the boiling point differences between nitrogen (-196 °C) and oxygen (-183 °C) and how this difference allows for their separation. The teacher also reminds pupils to draw appropriate diagrams for laboratory preparation of nitrogen from previous knowledge.
Pupils’ Activity: Pupils note the boiling points of nitrogen and oxygen and understand how these differences facilitate separation. They recall and discuss diagrams for laboratory preparation.
Learning Point: Pupils grasp the core principle of separation by fractional distillation based on boiling points.

Step 4: Physical Properties of Nitrogen

Time: 7 minutes
Teaching Skill: Description/Listing
Teacher’s Activity: The teacher describes the physical properties of nitrogen, such as its colourless, odourless, and tasteless nature, its density compared to air, and its solubility in water. The teacher also states its melting and boiling points.
Pupils’ Activity: Pupils listen, observe, and write down the physical properties of nitrogen as explained by the teacher.
Learning Point: Pupils identify and record the key physical characteristics of nitrogen.

Step 5: Chemical Properties of Nitrogen

Time: 7 minutes
Teaching Skill: Explanation/Examples
Teacher’s Activity: The teacher explains the chemical properties of nitrogen, focusing on its general unreactivity under normal conditions. The teacher then discusses its reactions with active metals and oxygen at high temperatures, providing relevant chemical equations.
Pupils’ Activity: Pupils listen to the explanations, copy the chemical properties and equations into their notes.
Learning Point: Pupils understand the chemical behaviour of nitrogen and the conditions under which it reacts.

Step 6: Explanation for Nitrogen’s Unreactivity

Time: 3 minutes
Teaching Skill: Explanation/Reasoning
Teacher’s Activity: The teacher explains the primary reason for nitrogen’s unreactivity, which is the strong triple covalent bond (N≡N) between its atoms, requiring a high amount of energy to break.
Pupils’ Activity: Pupils listen and understand the structural reason behind nitrogen’s stability and unreactivity.
Learning Point: Pupils identify the triple bond as the cause of nitrogen’s low reactivity.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Explain the industrial preparation of nitrogen from liquid air.
List three physical properties of nitrogen.
State two chemical properties of nitrogen.
Why is nitrogen generally unreactive at room temperature?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarizing
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the industrial preparation of nitrogen and its properties. The teacher then assigns homework: “Draw a labelled diagram of the fractional distillation column used for separating liquid air.”
Pupils’ Activity: Pupils listen to the summary and copy down the assigned homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Nitrogen – A chemical element, the most abundant gas in Earth’s atmosphere.
Liquid Air – Air that has been cooled to a temperature where it condenses into a liquid state.
Fractional Distillation – A process used to separate components of a liquid mixture with different boiling points.
Boiling Point – The temperature at which a liquid changes into a gas.
Unreactive – Not readily undergoing chemical reactions.
Triple Covalent Bond – A chemical bond between two atoms involving six bonding electrons.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research the uses of nitrogen in industry. For pupils requiring additional support, the teacher will provide simplified diagrams and allow for peer-to-peer explanation and guided note-taking during the lesson.

Note for teachers using this lesson plan

Teachers should ensure that diagrams for the industrial preparation of nitrogen are clear and well-explained. Emphasize the concept of boiling point differences for fractional distillation. Encourage pupils to actively participate in discussions about nitrogen’s properties and its importance.