Class VI: Chemistry : Air and Atmosphere

Air and Atmosphere

The Atmosphere: The layer of air that surrounds the Earth is called the Atmosphere. 

The atmosphere has five layers.

1. Troposphere: This layer is closest to the surface of the Earth. The troposphere starts at the Earth's surface and extends 8 to 14.5 kilometers high (5 to 9 miles). This part of the atmosphere is the densest. Almost all weather is in this region.
2. Stratosphere: This is the layer next to the troposphere. Aircrafts usually fly in this layer. The ozone layer is present within this layer.
3.  Mesosphere:  It is the layer above the stratosphere and extends to 85 kilometers. Fragments of rock and dust (meteors) that enter the Earth's atmosphere burn up in this layer. 
4. Thermosphere: The thermosphere starts just above the mesosphere and extends to 600 kilometers high. Artifical satellites orbit the Earth in this layer.
5. Exosphere: It is the outermost layer of the atmosphere. extends up to 10,000 km. 

Why air is a mixture and not a pure substance? 

Reasons: 

1. The composition of air varies from place to place.
2. The different constituents of the air retain their original properties.
3. There is no specific chemical formula for air. 
4. The components of air can be separated by simple physical methods.

Constituents of Air:

Constituents of Air	Percentage by Volume	Properties and Uses
Nitrogen	78%	Nitrogen is an inert gas It does not support burning It is an important component of proteins in living things.
Oxygen	21%	Oxygen is chemically reactive gas It supports burning It is essential for respiration in living organisms.
Carbon Dioxide	0.04%	Carbon dioxide is a chemically reactive gas. It does not support burning. It is necessary for photosynthesis in plants.
Noble Gases such as argon, helium, neon, krypton and xenon	0.93%	These gases are inert means non-reactive. Helium, neon and argon are used to light signboards. Helium is used in weather balloons Krypton is used photography. Xenon is used in the manufacturing of semiconductors.
Water vapour	Variable	Water vapour present in the air is also called humidity. It is responsible for weather changes such as rain.
Impurities: Dust particles, carbon dioxide, sulfur dioxide, oxides of nitrogen	Variable	Impurities present in the air may lead to acid rain. These may also cause respiratory problems, skin diseases and cancer.

Importance of Air:

1. Respiration: All living things breath in the air. 
• Inhaled air: The air we breathe in is called inhaled air. The oxygen in the inhaled air is used to break down food and release energy. 
• Respiration: The process of breaking down food to release carbon dioxide, water and energy is called respiration.
• Exhaled air: The air we breathe out is called exhaled air. Exhaled air has more carbon dioxide than inhaled air.
• The process of respiration continuously releases carbon dioxide into the atmosphere. It can be summarized as
• Food  + Oxygen ------> Energy + Water vapour +  Carbon Dioxide
2. Photosynthesis : 
• Green plants manufacture food through the process of photosynthesis.
•  In this process, food is synthesized in the form of glucose in the presence of sunlight, water, and carbon dioxide. 
• Green plants have a pigment called chlorophyll which helps to carry out photosynthesis. 
• Water is broken down into hydrogen and oxygen with the help of sunlight. Carbon dioxide combines with hydrogen a nd oxygen to form glucose. This glucose is stored in the form of starch
•                                        sunlight 
• Carbon dioxide + Water ---------> Glucose + Oxygen
•                                          chlorophyll 

Respiration	Photosynthesis
The process of breaking down food to release carbon dioxide, water and energy is called respiration.	In this process, food is synthesized in the form of glucose in the presence of sunlight, water and carbon dioxide.
The oxygen in the inhaled air is used to break down food and release energy.	Green plants have a pigment called chlorophyll which helps to carry out photosynthesis.  Water is broken down into hydrogen and oxygen with the help of sunlight. Carbon dioxide combines with hydrogen and oxygen to form glucose. This glucose is stored in the form of starch
In this process, carbon dioxide is released.	In this process, Oxygen is released.
Food  + Oxygen ------> Energy + Water vapour +  Carbon Dioxide	sunlight  Carbon dioxide + Water ----------------> Glucose + Oxygen                                              chlorophyll

Why plants and animals are interdependent?
How photosynthesis and respiration are interrelated?

Ans: Plants and animals are interdependent because the carbon dioxide required by plants for the process of photosynthesis is released by animals during respiration and the oxygen required by animals for the process of respiration is released by plants during the process of photosynthesis.  

Why do we need to plant more trees? 
Give reasons: We should grow more trees.
Explain how the balance of oxygen and carbon dioxide is maintained in the air. 

Ans:  

• The carbon dioxide required by plants for the process of photosynthesis is released by animals during respiration
• The oxygen required by animals for the process of respiration is released by plants during the process of photosynthesis.  
• Thus the balance of oxygen and carbon dioxide is maintained in the air. 
• But, due to a continuous increase in deforestation (cutting down trees) and atmospheric pollution, the balance of oxygen and carbon dioxide gets disturbed.
• Therefore we need to plant and grow more trees to resume the balance of oxygen-carbon dioxide in the air. 

Burning = Combustion 

A chemical change (process) in which a substance combines with oxygen and releases energy in the form of heat and light is called burning or combustion.

Substances like wood, coal, paper and candles burn in the presence of air and release energy. Any substance that burns uses oxygen from the air and releases carbon dioxide into the air.

Fuels 

A substance that releases heat and light when burnt in the air is called fuel. During burning, fuels use oxygen and release carbon dioxide into the atmosphere. 

Fuel + Oxygen ------> Heat + Light  +Carbon Dioxide  +Water vapour 

Based on their physic state fuels are classified into following three types:

• Solid Fuels: Wood and coal are solid fuels. 
• Liquid fuels: Kerosene, petrol and diesel are liquid fuels. They are obtained by the fractional distillation of petroleum.
• Gaseous fuels: Liquefied petroleum gas (LPG) and compressed natural gas (CNG) are gaseous fuels. They are also obtained by fractional distillation of petroleum

Uses of Fuels

• Fuels are used for cooking food because when combined with oxygen, fuels release energy in the form of heat which can be used for cooking. LPG and kerosene are used for cooking food. 
• Petrol and diesel are used in automobiles and machines.
• Kerosene is used in cooking stove and for lighting lamps.
• CNG is preferred fuel for running automobiles because it is cheaper and less pollution than other fuels.

Burning	Respiration
A chemical change (process) in which a substance combines with oxygen and releases energy in the form of heat and light is called burning.	The process of breaking down food to release carbon dioxide, water and energy, by living things, is called respiration.
The energy released in the process of burning is used in automobiles, machines and cooking food,	The energy released in the process of respiration is used by living things to grow.
A substance + oxygen ----à Heat  +  Light + Carbon dioxide	Food  + Oxygen ------> Energy + Water vapour +  Carbon Dioxide

Why is nitrogen considered so important for organisms? 

Ans: Nitrogen is the major component of air (78%) and is an essential nutrient for all organisms because

•  It forms the building blocks of proteins, enzymes and other cellular constituents which are essential for all forms of life.Proteins make up our skin, hair and help in carrying out various processes in the body like digestion of food, growth, and repair. 
• Plants need nitrogen for growth and it forms an important constituent of chlorophyll.

What is Nitrogen fixation? How do organisms obtain Nitrogen?

Ans: The process by which free nitrogen in the air is converted to soluble nitrate with the help of blue-green algae and certain types of bacteria living in the soil is called nitrogen fixation. 

Most of the organisms cannot use the nitrogen directly from the atmosphere. It becomes available to organisms when it is converted into soluble nitrogen compounds (nitrates or fixed nitrogen). the soluble nitrogen compounds are absorbed easily by plants from the soil. Other organisms get nitrogen when they consume the plants.

Explain the term air pollution. List three air pollutants.

Ans: 

Air Pollution

The release of harmful substances such as hydrogen sulphide, sulphur dioxide and carbon monoxide into the air is called air pollution

Air pollutants:

• hydrogen sulphide
• sulphur dioxide
• carbon monoxide

Common sources of air pollution

• Automobile exhaust
• Thermal power plants that burn coal to produce electricity
• Factories that burn fuels and release polluting gases.

Air pollution can be controlled by

• growing more trees
• setting up factories in non-residential areas
• using eco-friendly, non-polluting products
• controlling deforestation
• using chimneys and filters in industrial complexes to absorb pollutants

Global Warming :

The increase in the temperature of the Earth's atmosphere due to the increase in the concentration of gases such as carbon dioxide is called global warming.

What causes global warming?
Ans: Activities like deforestation and the burning of fossil fuels increase the concentration of carbon dioxide, methane, nitrous oxide, water vapour and other gases in the atmosphere. These gases prevent solar radiation reflected from the Earth's surface from returning to space. Due to this, the temperature f the Earth increases and leads to global warming. 

Class VI : South America - Location, Political Divisions and Physical Features

South America - Location, Political Division and Physical Features

Facts about South America

• South America is the fourth largest continent in the world.
• South America is also known as Latin America along with Mexico and the countries of Central America.
• It is connected with North America by a narrow stretch of land called Isthmus of Panama.
• the southernmost point of South America is Cape Horn.
• The southern part of the continent is very close to Antarctica. 

Location of South America

• Latitudes: It extends between 13°N and 55°S
• Longitudes: It extends between longitudes 35°W and 81°W
• South America is surrounded by water bodies on all four sides, the Atlantic ocean in the East, the Pacific ocean in the West, the Caribbean sea in the North.
• In the south, the Strait of Magellan separates the main continent from the island of the Tierra del Fuego.
• Most of South America lies within the Tropic of Capricorn.
• The Equator passes through the northern part of the continent.
• There are some well-known islands off the coast of South America. Some of the islands in the Pacific oceans are South Georgia, Trinidad, Falkland Islands (Malvinas) and the Galapagos.

Discovery and Exploration

1. The year 1498: Christopher Columbus explored the northern coastline of South America.
2. 16th Century: Spanish conqueror Francisco Pizarro arrived in South America to find the treasure and conquer this rich land.
3. Incas were the native people of South America. With the help of superior weapons and military tactics, Pizarro’s army conquered Inca Empire. But the traditions of Incas lived on.
4. 16th Century: A Portuguese explorer and navigator Pedro Alvares Cabral discovered Brazil.
5. The colonies of Spain in South America got their independence in the first half of the 19th Century.

Political Divisions

• There are 13 countries in the mainland of South America. 
• Different forms of Government found in South America are - presidential, federal, democratic and dictatorship
• Chile and Brazil are the largest democratic countries in South America continent.
• The two main languages spoken in South America are Spanish and Portuguese.
• Brazil is the largest country in the South America continent.

Physical Features
The continent of South America can be divided into four physical features

1. Western coastal strip
2. Central Plains
3. Western mountains
4. The Eastern Highlands

Western Coastal Strip :

• The Western Coastal Strip lies between the Andes mountains and the Pacific ocean all the way from northern part of the continent down to the south.
• It is widest in the northern parts. 
• Atacama Desert : 
• The Atacama Desert also lies in this Western Coastal Strip.
• It is one of the driest deserts in the world: Why ?  
• 
• Atacama desert is located at a high altitude of 2500 m from sea level where the air is dry.
• Also, the Andes mountains run along the Atacama desert acting as the natural barrier between the coastal desert on one side and the Amazon forest on the other side. It blocks all the moisture from Amazon. 
• Therefore Atacama desert is the driest desert in the world.
• The middle and the northern part of the desert run along the Pacific coastline of Chile and the remaining part runs into Peru.

Western Mountains :

• The Western mountains are also known as the Andes mountains.
• These are the continuation of the North American Western Cordilleras.
• The Andes mountains:  Facts
• These are the young fold mountains.
• Length of the Andes mountains is 7,2,42km.
• These mountains pass through seven countries in South America, namely, Argentina, Chile, Peru, Ecuador, Bolivia, Colombia and Venezuela
• The Andes mountains are the longest mountain ranges in the world.
• The Andes are the second highest mountains in the world.
• The highest peak in the Southern Hemisphere is Mount Aconcagua in Chile (6,962 m). They dominated the life of the native Incan society in South America. Its peaks were worshiped as gods.
• These mountains create a natural barrier between coastal desert on one side and the forests on the other side.
• The Andes continue under the South Atlantic Ocean and emerge in the continent of Antarctica as the Trans-Antarctic Mountains.
• The snow-capped mountains have deep gorges.
• These are the three chains of mountains.
• There are many active volcanos like Ojos Del Salado, Chimborazo and Cotopaxi.
• The widest part of the Andes mountains is in Bolivia and Peru with several plateaus and basins between them.
• Altiplano is an enormous plateau located at an altitude of about 6000 m. It has the highest lake in South America - Lake Titicaca.
• The entire region of Andes mountains is prone to earthquakes and is volcanic in nature. Therefore it is a part of the Pacific Ring of Fire.

Central Plains :

• The central plains are also called as Central Lowlands.
• They are found between the Eastern Highlands and the Andes mountains.
• These plains consist  of three river basins, the Orinoco Basin, the Amazon Basin and the La Plata River Basin,
• All these three rivers drain into Atlantic ocean.

1. The Orinoco Basin 
• The Orinoco basin is in the North part of South America.
• It is drained by the Orinoco river. 
• The source of the Orinoco river is in the Guiana Highlands and it flows into the Atlantic ocean.
• The Orinoco river crosses the Llanos of Venezuela. It is a navigable river.
• The basin is covered with tropical grasslands called Llanos which means plains.
2. The Amazon Basin
• The Amazon basin is drained by the Amazon river and its many tributaries.
• The Amazon river is the largest river in terms of volume of water and is the second longest river in the world after the Nile. 
• It originates in Peru.
• Smaller ships can travel all the way to Iquitos in Peru.
• The Amazon basin is an area of rainforests called Selvas. Mostly hardwood trees are found in this rainforest.
3. The La Plata River Basin

• This is wild, fertile basin in the south part of South America.
• It is drained by three rivers, the Parana, Paraguay and Uruguay.
• These rivers flow into the estuary (tidal mouth of the large river) Rio de la Plata, the widest estuary in the world on the southeastern coast of South America.
• The region at the north of this basin is called the Gran Chaco.
• The central area consists of miles of flat grasslands of Argentina called the Pampas.
• Below the Pampas are the drier regions of Patagonia which is called as Patagonian Plateau. 
• The Patagonian Desert is a part of the plateau. 

Eastern Highlands :

•  The eastern highland can be divided into

1. The Guiana highlands: These highlands lie to the North of the Amazon.  The highest waterfall - the Angel Falls is located in this highlands.
2. The Brazilian Highland: These highlands lie in the south-east.
3. The Patagonian Plateau:  this plateau lies close to the Andes mountains in the South.

• These highlands are composed of old rocks that contain important minerals.
• They are lesser in height than the high mountains in the west because of the effect of erosion over centuries. 

Rivers in South America

1. The Amazon River : 
• The Amazon river is the largest river in terms of volume of water and is the second longest river in the world after the Nile. 
• It is the largest river in South America.
• It originates in Peru.
• It has more than 1,000 tributaries.
• Rising high in the Andes mountains it irrigates almost half of the continent.
• Smaller ships can travel all the way to Iquitos in Peru.
2. The Orinoco River : 
• It is one of the longest rivers in South America.
• It flows like a giant arc from Colombia and Venezuela all the way to the Atlantic ocean.

Lakes in South America

• Lake Titicaca:
• It is the highest lake in the world
• It is the largest lake in South America in terms of volume of water.
• It is situated between Peru and Bolivia.
• It consists of two parts that almost look like two different lakes.
• Lake Maracaibo:

• It has a larger surface area. 
• It is connected to the Caribbean sea via the Gulf of Venezuela. Therefore, technically it is a bay rather than a lake.
• Lake Licancabur:

• It is the highest lake in the world. It is crater lake.
• It is situated in Chile, near the border with Bolivia.

Differences :

Atacama Desert	Patagonia Desert
Atacama Desert lies in this Western Coastal Strip.	Patagonia desert lies in Central Plains. The Patagonian Desert is a part of the Patagonian plateau.
Andes mountain runs along the Atacama desert	This desert lies close to the Andes mountain in the south.
This is the driest desert in the world.	This is less dry than the Atacama desert.

River Amazon	River Orinoco
It is the largest river in South America.	It is the longest river in South America
This river drains the Amazon Basin	This river drains the Orinoco basin.
The Amazon basin is an area of rainforests called Selvas. Mostly hardwood trees are found in this rainforest.	The basin is covered with tropical grasslands called Llanos which means plains.

The Orinoco Basin	The La Plata River Basin
The Orinoco basin is in the North part of South America.	This is wild, fertile basin in the south part of South America
It is drained by the Orinoco river	It is drained by three rivers, the Parana, Paraguay and Uruguay
The source of the Orinoco river is in the Guiana Highlands and it flows into the Atlantic ocean.	These rivers flow into the estuary (tidal mouth of the large river) Rio de la Plata, the widest estuary in the world on the southeastern coast of South America.

The Eastern Highlands	The Western Highlands
The eastern highlands are divided into three parts, the Guiana Highlands, the Brazilian Highland and the Patagonian Plateau	The Western Highlands are also known as Andes mountains.
Mountains in these highlands are lesser in height than the mountains in western highlands because of the effect of erosion over centuries.	Highest peaks of South America are part of these Highlands.

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