Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Air
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Air
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Subject: Chemistry
Class: Senior Secondary 2
Term: 1st Term
Week: 2
Theme: Chemistry And Environment
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list the constituents of air list the percentagecomposition of air state the properties of air draw, label and explain the various zonesof flame
zones with varying temperatures and chemical reactions. Diagram of a Luminous Flame (Teacher should draw this on the board and guide students): ``` /\ / \ / \ / \ (Hottest) / \ (Outer Non-Luminous Zone - pale blue/invisible) | | | YELLOW | | LUMINOUS| (Luminous Zone - bright yellow) | CONE | | | | | (Coolest) \________/ (Dark Inner Zone - unburnt gas) | | |____| (Wick/Burner Jet) ``` Explanation of the Zones:
1. Dark Inner Zone (Innermost Zone): Appearance: Dark or opaque.
Composition: Contains unburnt fuel gas (e.g., methane for Bunsen burner, paraffin wax vapour for candle).
Temperature: This is the coolest part of the flame (around 300°C) because there is no oxygen for combustion.
Reaction: No combustion occurs here.
2. Luminous Zone (Middle Zone): Appearance: Bright yellow or orange, due to the incandescence (glowing) of unburnt carbon particles.
Composition: Contains partially burnt fuel, hot carbon particles, and limited oxygen.
Temperature: Moderately hot (around 800-1000°C).
Reaction: Incomplete combustion occurs here due to insufficient oxygen supply. The carbon particles are formed during the thermal decomposition of the fuel and then glow brightly. Soot (carbon) is often deposited from this zone.
3. Outer Non-Luminous Zone (Outermost Zone): Appearance: Pale blue or almost invisible.
Composition: Contains completely burnt gaseous products (e.g., CO2, H2O) and abundant oxygen from the surrounding air.
Temperature: This is the hottest part of the flame (around 1200-1500°C), where complete combustion takes place.
Reaction: Complete combustion occurs here because there is ample oxygen from the atmosphere.
Note: For a non-luminous (Bunsen) flame, where the air hole is fully open, the flame is primarily blue and non-sooty, indicating complete combustion throughout and often only two distinct zones (a small dark inner zone and a larger pale blue non-luminous outer zone). 2.1 Constituents of Air Air is a mixture of gases that surrounds the Earth.
It is not a compound because: Its components are not chemically bonded. Its components retain their individual properties. Its composition can vary slightly. It can be separated by physical means (e.g., fractional distillation of liquid air). The constituents of air can be broadly categorized into: Permanent (Major)
Constituents: These gases are present in relatively fixed proportions.
Nitrogen (N2): The most abundant gas. It is relatively unreactive (inert) due to its strong triple covalent bond, but vital for plant growth (nitrogen fixation) and manufacturing fertilizers.
Oxygen (O2): Essential for respiration (breathing) in living organisms and supports combustion (burning). It is a reactive gas.
Argon (Ar): An inert noble gas.
Carbon Dioxide (CO2): Present in small but crucial amounts. It is essential for photosynthesis in plants and plays a significant role in the Earth's climate (greenhouse gas).
Variable (Minor)
Constituents: These gases are present in varying amounts depending on location, time, and environmental conditions.
Water Vapour (H2O): Varies greatly depending on humidity. Influences weather patterns (clouds, rain).
Other Noble Gases: Neon (Ne), Helium (He), Krypton (Kr), Xenon (Xe) – present in trace amounts, mostly inert.
Pollutants: Smoke, dust, sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), methane (CH4), etc. These are typically human-induced and vary significantly in concentration, especially in urban or industrial areas. 2.2 Percentage Composition of Air (by volume, dry air) The approximate percentage composition of dry air (excluding water vapour) is: Nitrogen (N2): 78% Oxygen (O2): 21% Argon (Ar): 0.9% Carbon Dioxide (CO2): 0.03% (often rounded to 0.04% in modern contexts due to increase) Other Noble Gases (Ne, He, Kr, Xe): 0.002% Other Trace Gases: Variable It is important for learners to understand that these percentages are for dry air. The presence of water vapour can reduce the relative percentages of other gases. 2.3 Properties of Air 2.3.1 Physical Properties: Colourless, Odourless, Tasteless: Pure air has no distinct colour, smell, or taste.
Transparent: Allows light to pass through it.
Gaseous State: At standard temperature and pressure.
Occupies Space: Air takes up space, as demonstrated by inverting a beaker into water.
Has Mass: Though light, a given volume of air has mass.
Exerts Pressure: Atmospheric pressure, vital for weather systems and demonstrated by simple experiments (e.g., collapsing can, drinking with a straw).
Slightly Soluble in Water: This allows aquatic life to breathe (fish use dissolved oxygen).
Bad Conductor of Heat and Electricity: Makes air an excellent insulator. 2.3.2 Chemical Properties: Supports Combustion: Due to the presence of oxygen, air allows substances to burn.
Supports Respiration: Oxygen in the air is essential for cellular respiration in living organisms.
Inert Nature of Nitrogen: Nitrogen does not readily react with most substances, acting as a diluent for oxygen and preventing rapid combustion.
However, it can react under specific conditions (e.g., lightning, Haber process).
Reactivity of Oxygen: Oxygen readily reacts with many elements and compounds (oxidation, rusting of iron).
Role of Carbon Dioxide: Participates in photosynthesis, dissolves in water to form weak carbonic acid (contributing to acid rain with pollutants). 2.4 Zones of a Luminous Flame A flame is the visible, gaseous part of a fire. When substances burn, they produce a flame. A luminous flame, such as that produced by a Bunsen burner with a partially closed air hole or a candle, is characterized by its yellow colour and sootiness, indicating incomplete combustion. It has distinct zones with varying temperatures and chemical reactions. Diagram of a Luminous Flame (Teacher should draw this on the board and guide students): ``` /\ / \ / \ / \ (Hottest) / \ (Outer Non-Luminous Zone - pale blue/invisible) | | | YELLOW | | LUMINOUS| (Luminous Zone - bright yellow) | CONE | | | | | (Coolest) \________/ (Dark Inner Zone - unburnt gas) | | |____| (Wick/Burner Jet) ``` Explanation of the Zones:
1. Dark Inner Zone (Innermost Zone): Appearance: Dark or opaque.
Composition: Contains unburnt fuel 3.1 Teacher Activities: Introduction (10 min): Begin by asking learners to brainstorm what air is and why it is important to life in Nigeria (e.g., breathing, cooking, flying planes). Display charts or visuals showing the Earth's atmosphere and the presence of air. Briefly introduce the lesson objectives.
Constituents and Composition (15 min): Present a chart or diagram detailing the major constituents of air and their approximate percentages. Explain the difference between permanent and variable constituents, giving examples relevant to Nigeria (e.g., water vapour varies in dry season vs. rainy season; pollutants higher in Lagos than a rural village). Emphasize why air is a mixture and not a compound.
Properties of Air (20 min): Physical Properties: Conduct simple demonstrations: Air occupies space: Invert an empty beaker into a trough of water, show water cannot enter fully.
Air has mass: Use two balloons, one inflated, one deflated, on a balanced stick.
Air exerts pressure: Use a plastic cup filled with water covered with cardboard, then invert it. The cardboard remains (briefly). (Alternatively, discuss straw effect, or collapsing plastic bottle with hot water then cap).
Solubility in water: Show fish tank or discuss bubbles released when water is heated.
Chemical Properties: Discuss the roles of oxygen (combustion, respiration), nitrogen (inertness), and carbon dioxide (photosynthesis, greenhouse effect). Perform a simple demonstration of oxygen supporting combustion (e.g., burning a candle, then covering it with a jar to show it extinguishes as oxygen is consumed).
Zones of Flame (25 min): If available, light a Bunsen burner to produce a luminous flame (partially closed air hole). Clearly point out and describe the three zones: dark inner, luminous yellow, and non-luminous outer. Explain the temperature differences and types of combustion in each zone. Alternatively, use a burning candle to demonstrate the zones, highlighting similarities and differences with a Bunsen flame. Guide learners in drawing and labelling the flame structure on their notebooks.
Conclusion (5 min): Summarize the main points of the lesson. Address any lingering questions. 3.2 Student Activities: Active Listening and Note-taking: Learners listen attentively and take notes on the constituents, percentages, and properties of air.
Observation: Learners observe teacher demonstrations on properties of air and the zones of a flame.
Participation: Respond to questions, contribute to discussions, and ask clarifying questions.
Drawing: Learners draw and label the three zones of a luminous flame as guided by the teacher.
Group Discussion: In small groups, learners discuss the importance of individual air components in everyday life in Nigeria (e.g., oxygen in hospitals, nitrogen in fertilizers).
Question 1: List the four most abundant gases in dry air and state their approximate percentage composition by volume.
Solution 1: The four most abundant gases in dry air are: Nitrogen (N2): Approximately 78% Oxygen (O2): Approximately 21% Argon (Ar): Approximately 0.9% Carbon Dioxide (CO2): Approximately 0.03%
Commentary: This question tests direct recall of the major constituents and their relative abundance, which is fundamental to understanding air composition.
Question 2: State two physical properties and two chemical properties of air.
Solution 2: Physical Properties of Air (any two from below): It is colourless, odourless, and tasteless. It occupies space. It has mass. It exerts pressure. It is slightly soluble in water. Chemical Properties of Air (any two from below): It supports combustion (due to oxygen). It supports respiration (due to oxygen). It allows for the rusting of iron (due to oxygen and water vapour). Nitrogen in air is relatively inert. Carbon dioxide in air is used for photosynthesis.
Commentary: This assesses understanding of both observable characteristics and reactive behaviours of air as a mixture.
Question 3: Draw a simple diagram of a luminous flame and label its three main zones. Briefly describe the characteristics of the hottest zone.
Solution 3: (Teacher will draw the diagram similar to the one in Section 2.4)
Labelled Diagram: Outer Non-Luminous Zone (or Pale Blue/Invisible Zone) Luminous Zone (or Bright Yellow Zone) Dark Inner Zone (or Unburnt Gas Zone) Wick/Burner Jet Characteristics of the hottest zone (Outer Non-Luminous Zone): Appearance: Pale blue or almost invisible.
Combustion: Complete combustion occurs here.
Temperature: It is the hottest part of the flame (around 1200-1500°C) due to ample oxygen supply from the surrounding air allowing for efficient burning.
Commentary: This question tests the learner's ability to visualize, reproduce, and explain the key features of a flame, linking structure to function (temperature, combustion type).
Question 4: Explain why air is classified as a mixture and not a compound.
Solution 4: Air is classified as a mixture and not a compound for the following reasons: Variable Composition: The components of air are not present in a fixed ratio by mass or volume; the amount of water vapour and pollutants, for example, varies considerably.
Retained Properties: Each component of air retains its individual chemical properties (e.g., oxygen still supports combustion, nitrogen remains largely unreactive). In a compound, original properties are lost.
Physical Separation: The components of air can be separated by physical means (e.g., fractional distillation of liquid air) without chemical reactions. Components of a compound can only be separated by chemical means.
No Chemical Bonding: The constituents of air are not chemically bonded together.
Commentary: This question probes a fundamental conceptual understanding of the difference between mixtures and compounds, using air as a concrete example.
Air Pollution and Health in Nigerian Cities: Many Nigerian cities, like Lagos, Kano, and Port Harcourt, suffer from significant air pollution due to exhaust fumes from old vehicles, emissions from numerous generators, industrial activities (e.g., cement factories, oil refineries), and open burning of waste. Understanding air composition helps learners grasp why pollutants like carbon monoxide (CO), nitrogen oxides (NOx), and sulfur dioxide (SO2) are dangerous. This knowledge can foster awareness about respiratory diseases and the need for environmental protection initiatives.
Industrial Utilization of Air Components: Nigeria's burgeoning industrial sector relies on components of air. For instance, oxygen is crucial in steel production, welding, and hospitals for medical support. Nitrogen is vital for the production of ammonia (Haber process) which is then used to make fertilizers (e.g., by Notore Chemical Industries), essential for Nigeria's agricultural sector. Learners can appreciate the economic value derived from understanding air chemistry.
Combustion and Energy Generation: From cooking with kerosene stoves and gas cylinders to powering homes and businesses with generators, combustion is a daily reality in Nigeria. Understanding the role of oxygen in combustion and the zones of a flame helps in optimizing burning efficiency (e.g., adjusting air holes in stoves for blue, non-sooty flames) and preventing the formation of harmful products like carbon monoxide from incomplete combustion, which is a significant household hazard.