CONSTITUENTS OF AIR PROPERTIES OF AIR AND AIR POLLUTION

TOPIC: AIR

CONTENTS:

1. CONSTITUENTS OF AIR
2. PROPERTIES OF AIR
3. AIR POLLUTION

4.FLAME

PERIOD 1:  CONSTITUENTS OF AIR

Air is a mixture of gases, composed mainly of nitrogen and oxygen with small amounts of Carbon (iv) oxide, noble gases and water vapour. The constituents of air can be separated easily by physical methods. Nitrogen accounts for about 4/5 of the atmosphere by volume, while oxygen occupies the remaining 1/5

Percentage composition

The chief natural constituents of air and their percentage composition by volume are as follow:

PERIOD 3: PROPERTIES OF AIR

1. Water vapour in air: The presence of water vapour or moisture in the atmosphere is due to the evaporation of water from the oceans, rivers, lakes, sea and water reservoirs. The amount present in air varies with temperature, the prevailing weather and the position of the place.
2. Noble gases in air: Argon is the most abundant of the bobble gases in the air, then neon. Noble gases are generally in reactive. They are used to produce colourful light for advertisement.
3. Carbon (iv) oxide air: The presence of carbon (iv) oxide in air can be proved by the passage of air through aqueous solution of calcium hydroxide (lime water) or KOH. The percentage of carbon(iv) oxide in air is balanced and maintained by the process of respiration and photosynthesis
4. Oxygen in air: oxygen is the most active component of air. It supports life. The process of burning a substance in air is called combustion. Its major reactions include corrosion (rusting), respiration and combustion.

Corrosion: This is the change on metallic surface that is observed after being exposed to air for few days. The corrosion of iron is commonly known as rusting. This can be prevented by (a) Applying grease (b) painting exposed surface (c) coating with metal e.g. chromium

EVALUATION

1. Mention two substances that can be used to remove carbon (iv) oxide from air.
2. List 5 properties of air.
3. What is corrosion? How can it be prevented?
4. State the percentage by volume of CO₂ in the atmosphere.

PERIOD 3: AIR POLLUTION

Air pollution is the released of substances into the atmosphere in quantities that are harmful to lives.

Causes of air pollution

1. COMBUSTION OF FOSSIL FUEL SUCH AS COAL, GASOLINE AND PETROLEUM GASES.
2. RELEASE OF FREONS FROM AEROSOL CANS.
3. RELEASE OF POISONOUS GASES FROM CHEMICAL WARFARE

Air pollutants:

1. Particulate matter: these are materials which exist as micro-sized solids in the air. They include dust, smoke, soot, asbestos, heavy metals particles etc. some of these heavy metals are lead, cadmium, arsenic and mercury. Lead particles are released to the atmosphere from the combustion of petrol in the form of lead (ii) bromide. Exposure to lead pollution over a long period of time is dangerous. This can cause brain damage among children. It also cause irritability, aggressive tendencies and gastric disorder. Mercury causes poison while cadmium causes severe gastric disorder.
2. Oxides of carbon: carbon (ii) oxide is released into the atmosphere through incomplete combustion of fossil fuel. It causes brain damage when inhaled even in low concentration. In high concentration, it results to death because it combines with the haemoglobin thereby depriving the body of oxygen. Increased amount of carbon (iv) oxide in the atmosphere leads to increased retention of infra-red rays and hence further warming of the earth-a phenomenon known as greenhouse effect. Therefore carbon (IV) oxide is called greenhouse gas.
3. Oxides of Sulphur and nitrogen: Sulphur (IV) oxide is derived from burning of coal, the combustion and refining of petroleum and the smelting of mineral ores for extraction. Once Sulphur (IV) oxide is present in air, it is oxidized by atmospheric oxygen to Sulphur (VI) oxide. The Sulphur (VI) is washed out by rain which converts it to tetraoxosulphate (VI) acid. This is called acid rain. The effect of inhaling the Sulphur (IV) oxide and acid rain are as follow:

(a) Sulphur (IV) oxide causes respiratory disorder.

(b). Acid rain causes death of plants.

(c). Acid rain leads to corrosion of metals, aging of fabrics, stiffening and crackin of leather, and destruction of buildings made of limestone

Nitrogen (ii) oxide causes depletion of ozone layer, and nitrogen (iv) oxide results to acid rain

4. Gaseous hydrocarbons and chlorofluorocarbons: some hydrocarbons in the air are the volatile ones such methane. They have carcinogenic effect in man and animal. Methane is also a greenhouse gas. Chlorofluorocarbons deplete the ozone layer. This exposes the earth to ultra-violet rays which causes skin cancer, sunburns and their ailments.

EVALUATION:

1. What is air pollution?
2. State four air pollutants
3. What is global warming? Name two greenhouse gases.

PERIOD 4: FLAMES

Flames are produced when substances burn. A flame is a region where gases combine chemically, with the production of heat and light. The type of flame produced depends on the nature of the substance that is burning. A flame may be luminous (brightly seen and yellow) or non – luminous (barely seen). Types of flame can be explained further using hydrogen, candle and Bunsen flames as examples.

• Hydrogen flame: Hydrogen burns with a very faint, non- luminous flame. The structure is simple, consisting of only regions: the unburnt gas zone and the zone of complete combustion.
• Candle flame: A candle burns with luminous flame four zones can be identified in the flame.
• The zone of unburnt gas around the wick
• The bright yellow luminous zone where there is incomplete burning of the hydrocarbon due to insufficient air supply
• The barely visible, non- luminous zone on the outside where complete of carbon particles take place due to sufficient air supply
• The blue zone at the base of the flame which also a region of complete combustion.

• Bunsen flame: A Bunsen burner is built with an air inlet of the base of the burner tube so that a stream of air can be supplied to the flame together with the fuel gas.

It is important equipment in a school laboratory used for heating. The fuel for the burner is a mixture of hydrocarbon gas (methane and butane) and some hydrogen and carbon (II) oxide

Luminous Bunsen flame: to produce luminous Bunsen flame, the air hole at the base of the burner tube should be closed. The flame produced is high, bright, wavy and yellow but not hot.

Non- luminous Bunsen flame: To produce non- luminous Bunsen flame, the air hole should be kept open. The flame is much hotter, cleaner and more compact than the luminous Bunsen flame.

EVALUATION:

1. Define flame
2. Compare the luminous and non- luminous flame Bunsen flames.
3. Describe the structure of a candle flame and explain the formation the products obtained during the burning.

GENERAL EVALUATION:

OBJECTIVE TEST:

1.These gases burn with blue flames except.

(a) C₂H₂ (b) H₂ (c) CH₄ (d) CO (e) SO₂

1. All these are the causes of luminosity in flames except.

(a) Solid particles (b) size of material (c) solid particles and increased pressure (d) pressure (e) solid particles and increased temperature

3. Which of these is not necessary for metallic corrosion?

(a) SO₂ (b) water (c) heat (d) oxygen (e) CO₂

4. The most abundant noble gas in nature is

(a) Neon (b) Argon (c) Helium (d) Krypton (e) Radon

5. When air is passed through a tube containing finely divided copper, the component of air absorbed is (a) Nitrogen (b) Water vapour (c) noble gas (d) carbon (IV) oxide (e) oxygen

ESSAY TEST:

1. (a) List four examples of noble gases. (b) Compare the structure of luminous and the non- luminous.
2. Give the constituents of atmospheric air, and indicate its approximate percentage composition.
3. Define combustion. Combustion in air would be impossible in the absence of which gas?
4. Draw and label the structures of (a) hydrogen flame (b) candle flame
5. What is rusting and how can it be prevented. (b) Explain any two properties of air.