Science Form 1 - chapter 5

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CHAPTER 5

The Air Around Us

State what is air made of

Explain why air is mixture

State the everage percentage of nitrogen, oxygen

and carbon dioxide

Carries out activities that shows:

1. The percentage of oxygen

2. That air contains water vapour,

microorganisms and dust

5.1 What is air made of

All living things need air to live.We can fast for

a day or two without taking any food or water,

but how long can we live without air? Take a

deep breath and hold it as long as you can.

Then exhale onto your palm. Can you feel the

air coming out from your nostrils? We cannot

see the air but we know it is there.

Earth is surrounded by 30 kilometres of air: a

mixture of several different gases

mixed together in different proportions.

Unfortunately the air around us is becoming

polluted by the day. Can we live in polluted air?

What must we do to keep the air clean to save

ourselves and the rest of the world?

What Is The Composition Of Air ?

Air is a mixture of different gases. The pie chart shows

the composition of air by percentage. What is the

average percentage of nitrogen, oxygen, carbon

dioxide and inert gases in the air? Why is the word

‘average’ used in the

earlier question?

Oxygen

21%

Nitrogen

78%

Carbon

dioxide 0.03%

Inert gases

<1%

Air as Mixtures

Air over busy cities

often contains toxic gases such as sulphur dioxide

and carbon monoxide. Air over industrial areas may

even contain traces of hydrogen and methane in

addition to the other components of the air.

As a mixture, the composition of air

varies from place to place and time to

time.

Air also contains varying amounts of water

vapour.

It can vary from practically zero in the hot

deserts to

about 5% in the tropical forests.

Microorganisms such as bacteria and viruses are

also present in the air. Do you know that we often

catch common cold because of the

microorganisms in the air?

Why do we often detect the strong smell of disinfectants in

hospitals?

Chlorofluorocarbons, dust, grit,

smoke, and compounds of

lead are some of the tiny solid

particles that are contained in

the air. These particles often

pollute the air. What particle or

particles in the air cause haze?

Haze causes serious health problems.

People with asthma have died from breathing in hazy air.

What must we do to prevent the air from being hazy?

Ozone is a compound made up of

three oxygen

atoms chemically combined together.

It forms a

layer high up in the Earth’s

atmosphere.

This

layer protects the Earth from the

harmful

ultraviolet rays of the Sun.

O3

Notes

Toxic gases, microorganisms, dust, smoke, grit,

chlorofluorocarbons (CFCs),

compounds of lead and ozone are also present in our air.

Air is a mixture of gases consisting of :

• Nitrogen

•Oxygen

•Inert gases

•Carbon dioxide

•Dust, microogranisms and water

vapour

78%

21%

<1%

0.03%

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CHAPTER 5

The Air Around Us

List the properties of oxygen and carbon dioxide

Identify oxygen and carbon dioxide based on their

properties

Choose suitable test for oxygen and carbon dioxide

5.2 Properties of Oxygen and Carbon Dioxide

is a colourless and odourless gas at room

temperature.

is soluble in water.

is very active as it readily combines chemically

with many substances to form new substances.

supports combustion as burning will not occur

without oxygen.

is needed for respiration by living things.

is produced by green plants during

photosynthesis.

Properties of Oxygen

is a colourless and odourless gas at room

temperature.

is slightly more soluble in water than oxygen.

Does not burn nor support combustion.

Is needed by plant to make food during

photosynthesis

is produced when living things respire, when carbon

or carbon compounds such as hydrocarbons and

carbonates are burnt and when carbohydrates such

as sugars and starch are fermented.

Dissolves in water to form weak acids

Properties of Carbon Dioxide

Properties Oxygen Carbon dioxide

Solubility in water Slightly soluble Slightly soluble

Solubility in sodium

hydroxide solutionNot soluble Very soluble

Effect on glowing

splinter

The splinter ignites

Oxygen supports burning

The splinter goes out

Carbon dioxide does not

support burning

Effect on burning

wooden splinter

The splinter burns brighter

Oxygen supports burning

The splinter goes out

Carbon dioxide does not

supports burning

Effect on moist blue

litmus paper or moist

red litmus paper

Oxygen has no effect on blue

litmus paper or 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

indicatorNo change

Changes the colour of

bicarbonate indicator from

red to yellow

State that energy, CO2 and water vapor are the products of

respiration

Relate that living things use oxygen and give out , CO2 during

respiration

Compare and contrast the content of oxygen in inhaled and

exhaled air in humans

State that oxygen is needed for respiration

Carry out experiment to show that living things use O2 and give

out CO2 during respiration

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CHAPTER 5

The Air Around Us5.3 Oxygen is needed in respiration

Respiration The process where our body obtains energy from

food is called respiration.

Respiration takes place in our body

Oxygen

Food

(Sugar)

Energy

Water Vapour

Carbon dioxide

Breath In Breath Out

Oxygen (O2) Carbon Dioxide (CO2)

INHALE EXHALE

Composition Inhaled Air Exhaled Air

Oxygen High (21%) Low (16%)

Carbon Dioxide Low (0.03%) High (4%)

Water Vapour Less More

Nitrogen No changes No changes

Composition Of Inhaled & Exhaled AIr

State what combustion is

State that oxygen is needed for combustion

List the products of combustion

Carry out experiments to investigate combustion

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CHAPTER 5

The Air Around Us5.4 Oxygen is needed for combustion

Combustion ?

Combustion is an oxidation reaction between a substance and oxygen

to give out

oxide (or oxides) and energy.

If the combustion is accompanied by flames, the process is called

burning.

Thus burning is a rapid combustion reaction between a substance and

oxygen giving out

light and heat.

When carbon (an element) burns in oxygen, an oxide is formed.

Charcoal, an example of carbon, burns in excess oxygen to produce

carbon dioxide gas.Carbon + oxygen →carbon dioxide

Condition for combustion ?

The presence of OXYGEN

The Presence of fuel

Enough amount of Heat is present

Combustion will not take place if any of these

condition is not present

Carbon + oxygen Heat energyCombustion

Light energy

Carbon Dioxide

+

+

Combustion of carbon

Combustion of hydrocarbon

Hydrocarbon + oxygen Heat energyCombustion

Light energy

Carbon Dioxide

+

+

Water

+

Explain what is air pollution

List examples of air pollutants

List the sources of air pollutants

Describe the effects of air pollution

Explain the steps needed to prevent and control air

pollution

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CHAPTER 5

The Air Around Us5.5 Air Pollution

We say that there is air pollution when there is a

SUBSTANCE THAT ARE HARMFUL to our health and can

cause damage to our environment are found in the air

POLLUTANTS

DUST

CO2 PESTICIDES

SMOKE

SULPHUR DIOXIDE

CARBON MONOXIDE NITROGEN OXIDE

The sources of air pollutants include motor vehicles,

factories, power plants, open burning and misuse of

pesticides

Air Pollutants Source of Pollutants

Gases (Carbon dioxide) and

smoke

Motor vehicles and factories

Carbon monoxide, sulphur

dioxide

Motor vehicles

Haze Open burning

Chlorofluorocarbon Aerosol spray, electronics

factories

EFFECTS OF AIR POLLUTION TO OUR HEALTH

Air Pollutant Effect

Asbestos particles Lung cancer

Gases from motor vehicles Liver failure and cancer

Carbon monoxide Headaches, brain damage or death

Sulphur dioxide

Bronchitis, pneumonia, lung cancer

Acid rain: damages plants and make

iron rust faster

Chlorofluorocarbon Causes damage to the ozone layer.

Too much exposure to UV rays can

cause, skin cancer, eye diseases and

the break-down of the body’s immune

system

Carbon dioxide Causes green house effect – Will result

global warming, changes in climate,

rising sea levels/ flooding

Describe how life would be without clean air

Suggest ways to keep the air clean

Practice habits that keep the air clean

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CHAPTER 5

The Air Around Us5.6 The Importance of Keeping the Air Clean

Steps to prevent air

pollution

Limit the use of CFC

in industry

Encourage the use of

biodiesel in cars

Encourage the

use of solar

energy

Avoid open burning

Relocate factories

away from urban

areas

Factories of chimneys

are built to a certain

heightMinimise

smoking habit

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