Chapter 5 The Air Around Us


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Chapter 5:

Chapter 5 The Air Around Us

The composition of Air 空气的组成:

The composition of Air 空气的组成 Air is matter It exist in the form of gas Air – main gases + inert gases, water vapour, microorganisms and dust

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The quantities of water vapour, microorganisms and dust are very small. Change with time and place. Water vapour -- changes with the weather Microorganisms -- cannot be seen because are too tiny Dust particles -- come from the soil and from the burning of fuels

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Water vapour Microorganisms Dust particles

Properties of oxygen and carbon dioxide:

Properties of oxygen and carbon dioxide Properties Oxygen Carbon dioxide Colour Colourless Colourless Odour Odourless Odourless Solubility in water Slightly Slightly Reaction with sodium hydroxide Not soluble Very soluble

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Properties Oxygen Carbon dioxide Effect on glowing and burning splinter Relight Extinguished Effect on moist litmus paper No effect Oxygen is neutral Blue to red Carbon dioxide is acidic Effect on lime water No effect Cloudy Effect on hydrogen carbonate indicator No effect Red to yellow. Carbon dioxide is acidic.

The role of Oxygen in Respiration:

The role of Oxygen in Respiration All living cells require O 2 to carry out its daily processes — respiration and production of energy O 2 is obtained from air through breathing Inhalation & exhalation Inhaled air – the air that is breathed in Exhaled air – the air that is breathed out

Respiration :

Respiration Chemical reaction process whereby O 2 is used to break down food to produce CO 2 , water and energy Glucose + O 2 → CO 2 + water + energy

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Cockroaches and germinating seeds take in oxygen and give out carbon dioxide during respiration. Carbon dioxide is absorbed by the sodium hydroxide solution The volume of air in the boiling tubes A and B are decreased, so the drop of the red inks moves towards the boiling tube.

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Living things give out carbon dioxide during respiration. Carbon dioxide is absorbed by hydrogen bicarbonate solution. The colour of indicator will change from red to yellow.

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Inhaled air Exhaled air N 2 (78%) Inert gas(1%) O 2 content CO 2 content Water vapour content Temperature 21% 0.03% Varies 25 0 C 16% 4% Concentrated 37 0 C

The role of Oxygen in Combustion:

The role of Oxygen in Combustion Combustion = chemical reaction which take place when fuel combines with oxygen Fuel, oxygen and heat are required Combustion will not take place if any of these conditions are not present

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Carbon + Oxygen → Carbon dioxide + Heat energy + Light energy Hydrocarbon + Oxygen → Carbon dioxide + Heat energy + Light energy + Water

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Manipulated variable: burning of candle Responding variable: volume of air left in the gas jar Constant variable: the air in the gas jar Showing that oxygen is needed for combustion

Slide 21:

Water filled up one-fifth of the original volume of the air in the gas jar. Means that, one-fifth of the air was used in the combustion of candle. Since oxygen makes up one-fifth of the volume of air, so the oxygen used in the combustion can be estimated 1/5 x 100% = 20%

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Manipulated variable: Size of beakers Responding variable: Time taken for the candles to burn Constant variable: Size of candles Finding out the effect of the size of a container on the length of time a candle burns

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A bigger container contains more air than a smaller container. A candle will burn for a longer time in a bigger beaker because there is more oxygen to support combustion.

Finding out the product of combustion of charcoal:

Finding out the product of combustion of charcoal

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Charcoal – consists carbon only, when burnt in air, the carbon combines with oxygen to form carbon dioxide (CO 2 ), whereas water is not formed. Kerosene – is a hydrocarbon (contains hydrogen and carbon). When burnt in air, the hydrogen and carbon combine with oxygen to form water (H 2 O) and carbon dioxide (CO 2 ).

Fire can be put out :

Fire can be put out Cut off the supply of oxygen To remove fuel To remove heat – use water to cool down the burning substance

Air Pollution:

Air Pollution

Air Pollution:

Air Pollution Occurs when there are pollutants in the air. Pollutants – harmful substances that are added to the air. – produced as a result of human activities – such as dust, CO 2 , pesticides … – dirty the environment and harmful to living thing.

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Gases and smoke from vehicles and factories contain carbon particles and soot.

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Burning of fuels such as petrol and diesel release carbon dioxide and water vapour.

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If the combustion of fuels is not complete, carbon and poisonous gas – carbon monoxide are formed. Sulphur dioxide and oxides of nitrogen are also formed. They can dissolve in rain water to form acid rain. In the past, compounds of lead were added to petrol because this will improve the combustion. However, the released gases contained lead particles are harmful to people.

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The forming of acid rain

The effect of acid rain:

The effect of acid rain

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The effect of acid rain

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Haze is caused by the open burning of forests and also by the release of excessive pollutants from vehicles.

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Effects of air pollution on human beings and the environment:

Effects of air pollution on human beings and the environment Cause mainly lung diseases and other health problem, such as: (a) asbestos particles – cause lung cancer. (b) gases from vehicle – cause liver failure and cancer (c) lead particles – damage children ’ s brains (d) carbon monoxide – cause headaches, brain damage or even death (e) sulphur dioxide – cause bronchitis, pneumonia and lung cancer

Thinning of Ozone Layer:

Thinning of Ozone Layer Ozone layer – acts as a natural filter for ultraviolet rays - destroyed by chlorofluorocarbon (CFC) compounds and speed up its thinning process

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CFC compounds : Given out when we use aerosol sprays Also used as coolants in air conditioners and refrigerators Thinning of ozone layer allows more ultraviolet rays to reach the Earth. Too much ultraviolet rays is harmful to living things, it cause skin cancer and damage to the eyes , kill the organisms that are useful to man

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Thinning of Ozone Layer

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Greenhouse Effect:

Greenhouse Effect Caused by excess carbon dioxide produced. It prevents the heat from the Earth from escaping into space and causes the temperature on the Earth to rise. The increase in temperatures will result in changes in climate, the rate of photosynthesis is decreased, amount of agricultural products will drop. It will also cause the ice in the North and South Poles to melt which results in rising sea-levels. This may flood low-lying area.

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