CHAPTER 5: AIR

Why is air a mixture ?

1.      The composition of air is not fixed.

2.     It changes according to  the time of the  day, the conditions of environment and humans’ activities.

3.     For example,

The air in a place which is crowded with people has a higher content of a carbon dioxide than the air in a less crowded place.

The air in a jungle has a higher content of oxygen than

the air in an industrial area.

The content of water vapour in the air is higher in the morning than in the afternoon.

4.      All these examples show that  the   percentage the

  components of air is not  always the same.

5.        Therefore, we can say that  air is a mixture.

THE                     PROPERTIES   OF   OXYGEN                       AND   CARBON   DIOXIDE.

What are the properties of oxygen and carbon dioxide?

1.      Oxygen  and carbon                            dioxide are two of most important gases in the air.

2.     Table below shows the properties of oxygen and carbon dioxide.

Properties	Oxygen	Carbon dioxide
Solubility in water.	Slightly soluble.	Slightly soluble.

Solubility in sodium hydroxide solution.	Not soluble.	Very soluble
Effect on glowing wooden splinter.	The splinter ignites. Oxygen supports burning.	The splinter goes out. Carbon dioxide does not support burning.
Effect on burning wooden splinter.	Splinter burns more brightly. Oxygen supports burning.	Splinter goes out. Carbon dioxide does not support burning.
Effect on moist blue litmus paper and red litmus paper.	Oxygen has no effect on blue litmus paper and red litmus paper. Oxygen is a neutral gas.	Blue litmus paper : Changes to red. Red litmus paper : No change of colour. Carbon dioxide is an acidic gas.
Effect on lime water.	No change	Lime water turns cloudy.
Effect on bicarbonate indicator.	No change	Changes the colour of bicarbonate indicator from red to yellow.

OXYGEN   IS   NEEDED                        IN                              RESPIRATION

1.      The process whereby our body obtains energy from food

is called respirations.

2.     Respirations takes place in the cells of our body.

3.     Oxygen is needed for respiration to take place.

4.     The products of respirations are energy, carbon dioxide and water vapour.

OXYGEN                           IS                               NEEDED    FOR   COMBUSTION

1. Combustion  is a chemical reaction which takes place when fuel

combines with oxygen.

2. Fuel is a substance which can burn. For example :

a.      Carbon like charcoal, coal and firewood.

b.     Hydrocarbon  like diesel, kerosene, gasoline (petrol), candle and natural gas.

3. The product of fuel combustion :

a.      Carbon.

Carbon   +   oxygen

carbon dioxide  + light energy +  heat   energy. 

 b. Hydrocarbon.

Hydrocarbon +  oxygen  --------  carbon dioxide  +

water +  light energy  +   heat energy.

AIR POLLUTION

1.      Air pollution refers to the presence of foreign particles in air which can affect the quantity of air and the health of living things.

2.     The sources and effects of air pollutants.

Air pollutant	Sources	Effects
Smoke particles and soot.	Cigarette smoke. Smoke from motor vehicles. Burning of rubbish. Burning of fossil fuels. Forest fires	Cause breathing difficulties. Make the eyes feel uncomfortable.
Dust	Construction sites Cement plants	Causes lung cancer, coughing and asthma.
Carbon monoxide	Cigarette smoke Smoke from motor vehicles	Causes tiredness, headache, brain damage and death.
Sulphur dioxide	Burning of coal	Damages lung cells Forms acid rain that damages metallic structures and kills aquatic life Kills plants
Oxides of nitrogen	Smoke from motor vehicles	Form acid rain

THE IMPORTANCE OF KEEPING THE AIR CLEAN

1.      Air is one of the basic needs of life.

2.     We would all suffer in many ways if they we no clean air for us to

         breath: It is unpleasant to smell dirty air. We may have breathing

         difficulties. We may cough continuosly.

         We may get lung diseases.

3.     We can help to keep the air clean by doing the following : Using

        public transport. Using unleaded fuel. Enforcing anti-air pollution
        
        laws.  Planting trees around the house.

 4.     Habits to keep the air clean : Do not smoke.

         Turn off the car engine while waiting for someone. Cycle or walk for
         
         short distance trips. Practice car-pooling.