Rusting Of Iron And Crystallization

Whether it is a change taking place within our body or in our surroundings, we know that changes can be broadly categorized as physical and chemical changes

Physical change

In a physical change, a substance undergoes a change in its physical properties.During this change, the formation of new substances does not take place and most of the physical changes are reversible. Evaporation, melting of butter, and cutting of paper are some examples of physical changes.

Chemical change

In a chemical change, the formation of one or more new substances takes place. The new substance formed has different chemical properties from that of the substance that formed it. Burning of fuels, cooking of food, fermentation, and souring of milk are some examples of chemical changes.

We will now discuss two important changes:

Rusting (a chemical change) and crystallization (a physical change)

You must have observed that when articles of iron are kept out in the open for some time, they get covered by a brownish substance. This brownish substance is called rust. Rust is the new substance obtained from the combination of iron and atmospheric oxygen. The characteristic properties of rust are different from that of iron as well as oxygen. Hence, rusting of iron is a chemical change, which affects articles of iron and slowly destroys them.

The two main factors that cause rusting are oxygen and water. As soon as the article comes in contact with air (oxygen) and moisture (water), it starts rusting. The chemical process that occurs during rusting can be represented as follows:

Iron (Fe) + Oxygen (O2) + Water (H2O) → Rust (Fe2O3)

Rusting becomes faster with an increase in the content of moisture in air. That is why water pipes made of iron tend to get rusted easily.

Salt makes the process of rusting faster. Rusting is a complex process involving many steps. The presence of salt speeds up the first step, which in turn speeds up the whole process.

Did you know?

Ships are made of iron and a part of them remain under water. Seawater contains many salts dissolved in it and salt water makes the process of rusting faster. Therefore, ships suffer a lot of damage. As a result, a fraction of the ship’s iron has to be replaced every year. Hence, a large amount of money is spent to replace the damaged iron and steel.

Every year, our world suffers huge monetary losses owing to the process of rusting, which causes harm to the articles made of iron. Therefore, attempts are being made to prevent rusting. Here are some ways that can prevent rusting.

1.1. Painting or coating iron articles with grease: This does not allow iron to come in contact with oxygen and water. Hence, it prevents rusting. In fact, paints and grease should be applied regularly to prevent rusting.

2. Rusting can also be prevented by depositing a layer of metal such as chromium or zinc on the surface of the iron article. The process of depositing zinc on iron is called galvanization.

Alloying is another method used for the prevention of rusting. Stainless steel is an alloy. It is a homogeneous mixture of iron, carbon, chromium, nickel, and manganese. It does not rust.

Now, let us discuss crystallization in detail, which is a physical change.

We know that evaporation is a physical process in which a substance changes from liquid to gaseous state. By evaporation, salt is obtained from seawater and all water changes to water vapour. As a result, only the non-volatile salt remains. The salt obtained by this method is not pure and has to be purified. Hence, purified crystals of salt can be obtained by the method of crystallization.

In the crystallization method, a saturated solution of a substance (to be purified) is made. Then, this solution is boiled to make it a supersaturated solution. When this supersaturated solution is cooled, crystals of pure substances are obtained. Thus, large crystals of pure substances can be formed from their solutions by the process of crystallization.

Since no new product has been formed, this is an example of physical change. Let us watch the following animation to understand the process of crystallization.their solutions by the process of crystallization.

Since no new product has been formed, this is an example of physical change. Let us watch the following animation to understand the process of crystallization.

PLEASE LIKE AND SHARE IT.

You must have observed that when ice melts, it changes to water. Similarly, when we burn paper, it changes to ash. Thus, in both cases, a change is taking place. There are many changes taking place all around us. Can we classify these changes? All the changes can be broadly classified into two types:

1. Physical changes

2. Chemical changes

Let us differentiate between physical changes and chemical changes.

We know that the shape, size, colour, and state of a substance are its physical properties. Physical changes usually involve changes in these properties of a substance. A change in any one of these physical properties is called a physical change.

For example, if you cut a piece of paper into 4 equal squares, then the shape of the paper changes, but there is no change in the properties of the paper. Also, no new substance gets formed in the process. Hence, the cutting of paper is a physical change.

                                 

In this case, we cannot join back the pieces to form the original paper. Hence, the cutting of paper is irreversible in nature. Let us now discuss a physical change, which is reversible in nature.

If we add a spoon of common salt in some water and stir the mixture for sometime, then the salt disappears. Now, if we place the salt solution in a china dish over a hot plate, then it will be observed that the water evaporates after sometime, leaving behind a white solid (as shown in the figure).

                                                  

The white solid that is left after all the water is boiled is nothing but salt. This proves that when salt dissolves in water, no new substance is formed. However, this process is reversible. Thus, dissolution of salt in water is a physical change.

Hence, it can be concluded that in a physical change,

• a change in the physical properties of a substance such as state, shape, size, and colour takes place
• no new substances are formed

For example,

Ice → Water →Steam (They are all still water)

• the original substance can generally be recovered again

Now, you know what physical changes are. Do you know the characteristics of chemical changes?

A chemical change is the one in which the formation of one or more new substances takes place. The new substance formed has different chemical properties from that of the substance that formed it.

Now, watch the following animation to see an example of chemical change.

You must have observed that when ice melts, it changes to water. Similarly, when we burn paper, it changes to ash. Thus, in both cases, a change is taking place. There are many changes taking place all around us. Can we classify these changes? All the changes can be broadly classified into two types:

1. Physical changes

2. Chemical changes

Let us differentiate between physical changes and chemical changes.

We know that the shape, size, colour, and state of a substance are its physical properties. Physical changes usually involve changes in these properties of a substance. A change in any one of these physical properties is called a physical change.

For example, if you cut a piece of paper into 4 equal squares, then the shape of the paper changes, but there is no change in the properties of the paper. Also, no new substance gets formed in the process. Hence, the cutting of paper is a physical change.

In this case, we cannot join back the pieces to form the original paper. Hence, the cutting of paper is irreversible in nature. Let us now discuss a physical change, which is reversible in nature.

If we add a spoon of common salt in some water and stir the mixture for sometime, then the salt disappears. Now, if we place the salt solution in a china dish over a hot plate, then it will be observed that the water evaporates after sometime, leaving behind a white solid (as shown in the figure).

The white solid that is left after all the water is boiled is nothing but salt. This proves that when salt dissolves in water, no new substance is formed. However, this process is reversible. Thus, dissolution of salt in water is a physical change.

Hence, it can be concluded that in a physical change,

• a change in the physical properties of a substance such as state, shape, size, and colour takes place
• no new substances are formed

For example,

Ice → Water →Steam (They are all still water)

• the original substance can generally be recovered again

Now, you know what physical changes are. Do you know the characteristics of chemical changes?

A chemical change is the one in which the formation of one or more new substances takes place. The new substance formed has different chemical properties from that of the substance that formed it.

Now, watch the following animation to see an example of chemical change.

Let us add more to our knowledge by performing the next activity.

When lime is added to water, the temperature of water increases and water almost starts boiling. A substance called slaked lime is produced during this change. Hence, it is a chemical change. The following chemical equation can be used to represent the chemical change.

CaO + H₂O → Ca (OH)₂ + Energy

Lime Water Slaked lime

Thus, it can be concluded that in a chemical change,

• one or more new substance(s) are formed
• the chemical properties of the new substance(s) are different from those of the starting material
• the original material cannot be recovered easily

For example, magnesium oxide and calcium hydroxide (formed in the above activities) cannot be converted back into their original substances.

Hence, we can summarize the differences between physical and chemical changes as given in the table below.

Physical Change	Chemical Change
1. The chemical composition of a substance does not change.	1. The chemical composition of a substance changes.
2. Most changes are reversible.	2. Most changes are irreversible.
3. No new substances are formed. For example, Ice → Water → Steam	3. New substances are formed.For example, Paper → Ashes

Can you specify the type of changes given in the table?

PLEASE LIKE AND SHARE ON FACEBOOK,TWITTER AND OTHER SOCIAL SITES.

Soil, Its Importance And Characteristics

Did you know that it takes a thousand years to form a one-inch thick layer of soil?

We find soil all around us. What is soil? What are its components? How is soil formed? What are the different layers of soil?

Let us explore the answers to the above questions.

Dig a pit in a suitable area using a spade. Collect a sample of soil from this pit and mix it with water in a glass jar. Stir well, and then allow the contents to settle. Observe the components.

What do you see?

Organisms like ants and earthworms, decaying leaves, plant roots, small pebbles, rock particles etc are commonly observed.

You will also see soil particles of varied colours, and sizes. These settle down at different regions in the glass jar. The larger and heavier particles settle at the bottom of the glass, while the finer soil particles form the top layer. Soil particles of intermediate size, form the middle layer. These are the components of the soil.

Decaying leaves and dead organisms are called Humus.

How is soil formed?

Soil is formed by a process called weathering. The process of weathering occurs as a result of the action of wind, water, or climatic changes.

Weathering is the process that breaks down large rocks into smaller pieces. These small pieces of rocks form soil by mixing with decaying plants and animal parts. 

Thus, is soil uniform throughout? Let us find out

Dig a deep pit vertically into the ground. What do you observe? Is the appearance of the soil same as you go deeper into the pit?

No. As we dig deeper, the nature of the soil changes in terms of its colour, contents, texture, chemical composition etc. Thus, different regions or layers of soil can be observed.

What are these layers of soil? Let us find out more

Safety Measures During Thunderstorm, Cyclone, And Tornadoes

Do you know that approximately 1, 40,000 people died in a cyclone that hit Bangladesh in 1991?

The cyclone that hit the state of Orissa in 1999 destroyed 17110 square kilometres of crop land. Approximately, 25 00 000 domestic animals died and the total loss of property was estimated to be about 4.5 billion dollars!

Thus, high speed winds are capable of causing large-scale destructions. Since their occurrence cannot be controlled therefore, knowledge of safety measures is of utmost importance.

Some of the safety measures to be followed are listed

• Pay heed to the warnings broadcasted by the authorities over the radio and television
• Floods cause damage to the roads. Therefore, all roads in flood-hit regions should be avoided
• Necessary arrangements should be made for the shifting of domestic animals, vehicles, household goods etc from cyclone hit areas to safer areas
• Emergency phone numbers of services like police, fire brigade, and medical centres should be known by all members of the family

Some precautions for cyclones include

• Floods follow cyclones. Therefore moving to a higher altitude area is recommended in order to avoid floods
• Going outside the house, particularly to the sea-shore, should be avoided during a cyclone
• Previously stored water should be used for drinking as water during cyclones may be contaminated
• Emergency supplies such as water and food, first-aid kits, etc should be stored by people living in cyclone-prone areas
• Construction of cyclone shelters in cyclone-prone areas is recommended. Construction of houses that can withstand cyclones should be encouraged, wherein plywood can be used instead of glass to make the windows.

• Broken switches and wires should not be touched during a cyclone as these can cause electric shock
• Rescue workers who provide support by supplying food, water, and medicine should be helped in their tasks
• We should help and cooperate with neighbours and friends who may need assistance during a cyclone

Some of the safety measures to be followed during tornadoes

• Constructing tornado shelters

• Shutting down of all the doors and windows

• Sitting underneath a bench or a table inside the house
• Bending on your knees and bowing down by protecting the head with your hands will help shield the body from fatal injuries
  Along with the knowledge of cyclones, advancements in science and technology can help develop better prediction and warning systems. This will help to combat emergency situations.
  With time, predictions about the occurrence of cyclones and tornadoes have become very accurate. With the help of satellites and radar systems, weather forecasters can warn people in advance about cyclones and tornadoes. Forecasters use watches and warning systems to help people in cyclone-hit areas.
  A cyclone watch is a weather alert that makes a forecast about cyclones that are likely to hit a particular area
  • For a storm, it is issued about two days in advance
  • A cyclone warning is a weather alert that is issued 24 hours in advance
  • Before cyclones hits the shoreline the message is broadcasted every 30 minutes
  These systems are used by several national and international agencies. An instrument used to study the speed of winds is the anemometer
  
  
  
  More about anemometers!
  Since the low-pressure area in a cyclone results in high-speed winds, it is very important to measure the speed of the winds. It helps the meteorologists to accurately predict the nature and extent of these natural disasters. You can measure wind speeds with the help of an anemometer that can be installed at the top of your house.
  
  

Wind Formation On Earth

Wind Formation On Earth

We have all felt the gush of wind. Why is this wind sometimes fast and at other times slow? How is wind formed and what causes it to move?

Let us first learn a few facts about air that would help us understand wind better.

Winds blow from a region of low temperature to a region of high temperature because of a difference in the atmospheric pressures.

A region with a high temperature has a low-pressure condition because of low air density. A region with a low temperature has a high-pressure condition because of high air density.

We understand that a pressure difference is important in the formation and movement of winds. However, what is responsible for creating this difference in pressure?

The pressure differences exist because of the uneven heating of the Earth’s surface.

What causes an uneven heating of the Earth’s surface?

The various factors responsible for the uneven heating of the Earth’s surface and thereby for the formation of winds are listed below.

[1] Different latitudes

Owing to the tilted rays of the Sun, both the poles receive a minimum amount of sunlight. This causes the air in these regions to remain relatively cold, thereby creating a high-pressure region. The air between the 30° to 60° latitude belts is warmer in comparison to the air near the poles. Hence, this warm air rises up and cold air from the Polar Regions rush in to fill the empty space. This is depicted in the above figure.

[2] Different heating of land and water

Have you ever heard of land breeze and sea breeze?

During the summer months, the equatorial land absorbs heat and the temperature of the land becomes higher than that of the oceans. This makes the hot air from the land rise up and the cold air from the oceans blow towards the land. This results in the formation of the monsoon winds.

During winter months, the temperature of the land becomes less than that of the oceans. As a result, winds start blowing from land to the oceans.

Monsoon rain

Monsoons are seasonal winds that change their direction with changing seasons. They blow from the oceans towards land in summer and from the land to oceans in winter. When blowing from oceans to land, these winds carry water droplets with them and are responsible for the rains in India.

Other factors that influence winds:

The rotation of the Earth affects the direction of wind currents.

The rotation of the Earth on its axis causes the day and night cycle. During the day, one-half of the Earth receives sunlight and the other half is dark. Because of the rotation of the Earth, the wind currents do not flow in a straight North-South direction, but tend to flow in a curved path. The force produced by the rotation of the Earth is known as Coriolis force. It affects the direction of winds.

Summer and winter seasons affect the speed of wind currents.

The seasons are caused by the revolution of the Earth around the Sun. Air near the Earth’s surface becomes very hot during the summer months. This hot air rises upwards and creates a region of a very low pressure. Cold air comes in very fast to fill this low-pressure space. This results in the occurrence of high-speed wind currents.

On the other hand, during the winter months, wind current blows at very low speeds because of minimal pressure differences between the hot air and cold air regions

Air Pressure

We have seen kites flying in the sky and the trees moving to and fro when the wind blows.

How do kites fly in the sky? What causes the trees to move back and forth when the wind blows?

The movement of kites and the swaying of trees are caused by the pressure exerted on them by air.

What is this air pressure?

Air pressure refers to the force exerted per unit area of surface by the air that is directly above that surface.

When air blows, it exerts pressure on the face of a kite and pushes the kite up in the sky. Similarly, when the wind blows, it exerts pressure on a tree and makes it bend in the direction of the blowing air.

Let us perform an activity to understand this.

Please perform the activity under adult supervision.

• Pour water into a metal can and boil over a stove keeping the can uncovered.
• After boiling for 2-3 minutes, cover the can with a lid.
• Using tongs, carefully place the can in the sink.
• Pour cold water over it.
  What do you observe? When cold water is poured over the can, it causes the can to crush.
  Water vapour condenses when cooled. It has more pressure. Therefore, when cooled, the vapour condenses, reducing the pressure. This compresses the metal can. Therefore, air exerts pressure.
  Let us look at some more instances where we feel the air pressure.
  • Cycling or rowing against the wind is difficult because of the pressure exerted by air.
  • The tyres of vehicles are filled with air, thereby exerting pressure. This makes it possible for them to hold and carry weight.
    
    Let us now explore another important property of air by performing an activity.
    Place a small paper ball inside the neck of a transparent bottle as shown and forcefully blow air into it.What do you observe?
    It is observed that it is difficult to push the small paper ball inside the bottle by blowing.
    This is because the speed of the wind is higher at the mouth of the bottle, thereby resulting in reduced air pressure near the mouth of the bottle.
    On the contrary, the wind inside the bottle has a low speed and therefore, a higher pressure as compared to that at the mouth of the bottle. This higher air pressure inside the bottle prevents the paper ball from entering the bottle.
    Therefore, high wind speed has low pressure and low wind speed has high pressure.
    Let us perform a small experiment.
    
    
    Let us look at another demonstration of this property. Place a strip of paper between your lips and forcefully blow out air. You will observe that the paper strip moves upwards.
    
    
    
    
    
    
    

Nitrogen Fixing Bacteria- Rhizobium

Nitrogen is essential for plants to make proteins. Plants cannot directly utilize the nitrogen available in the atmosphere. They require nitrogen in the soluble form.

How is atmospheric nitrogen supplied to plants in the soluble form without the use of fertilizers?

A bacterium called Rhizobium plays an important role in this process.

Rhizobium converts atmospheric nitrogen into the soluble form, which can then be taken in by plants. However, since Rhizobium cannot prepare its own food, it establishes itself in the roots of other plants and provides them with nutrients. Plants, in turn, provide the bacterium with food and shelter. Thus, there exists a symbiotic relationship between the bacterium and plants.

Rhizobium lives in the roots of gram, peas, moong, beans, and other leguminous plants. It is not present in the roots of all plants.

Do you know why farmers plant leguminous plants along with other crops in their fields?

Leguminous plants enrich the soil by fixing atmospheric nitrogen with the help of Rhizobium bacterium, which is present in their roots. They also help in reducing the use of fertilizers in the soil. It is for this reason farmers plant leguminous plant along with other crops in their fields.

                                          

                 INTRODUCTION TO PHOTOSYNTHESIS

                               by the super blogger prashant gupta