SOIL CHAPTER 9 CLASS 7 SCIENCE NOTE- STUDY MATERIAL

SOIL CHAPTER 9 CLASS 7 SCIENCE NOTES

                                SOIL 

There are many natural resources on earth. Soil plays an important role among them. Soil provides shelter for many animals. We can see many organisms in the soil which dwell their life in it. It helps human beings also in many ways. Our crops, forests, water resources, buildings, and constructions are very much related to the soil.

You can collect soil samples from different places and observe the kind of insects and small organisms present in them. Different plants and herbs can be seen in it. Tabulate your result and make a comparative study of it.

 

Collect a sample of soil from your garden. Put that soil in a transparent glass tumbler of water. Stir it properly and allow it to settle down. Observe the distinct layers seen in the tumbler.

We can see that the heavy gravel particles are settling at the bottom of the tumbler. Just above that layer, we can observe sand particles. Clay particles are finer and smaller than sand and hence it will be settling on top of the sand. There will be a muddy water layer just above the clay layer. Water will become more clear as time passes and it will be visible as a separate layer. Very lighter and less dense things will be floating on the top layers. It may include dry leaves, animal remains, and twigs.

HUMUS

The rotting dead matter of plants and animals present in the soil is called humus. Normally the top layer of the soil will be rich in humus.

SOIL PROFILE

How soil is formed on earth? Have you ever thought of the formation of soil on earth?

The soil we see today has been formed through different processes that occurred in nature. The rocks that were there on earth undergone many changes due to climate change, rain, heat, and flowing water. 

Water that gets collected in the cracks of rocks will be freezing at night and it expands to make bigger cracks on it. It started breaking down into smaller pieces and might have carried by the wind or water. 

The process of breaking down rocks into the soil by the action of wind, water, and climate is called weathering.

When you are taking a ride in a hilly place, you can see the vertical cross-section of soil through which the roads are made. Have you noticed the difference in the colour and texture of each layer?

SOIL PROFILE

The vertical section through various layers of soil is called a soil profile.

These layers in a soil profile are called horizon. Each horizon will be of different colour, texture, depth, and composition.

We can discuss the features of these horizons in detail.

A-HORIZON or TOPSOIL

• It is the uppermost layer of the soil.
• It is dark in colour as it is rich in humus and minerals.
• It is soft and porous.
• It can retain more water.
• It is a shelter for many animals.
• It helps the roots of plant to spread easily through the soil.

B-HORIZON

• It is the next layer to the topsoil.
• It has a lesser amount of humus.
• It has more amount of minerals.
• It is generally harder and more compact than the topsoil.

C-HORIZON

• It is the third layer of the soil profile.
• It is made up of small lumps of rocks with cracks and crevices.

BEDROCK

• It is the last layer of the soil profile.
• It is the hardest layer.
• It contains a bed of rock which is difficult to dig with a spade.

TYPES OF SOIL

Soil formed from rocks in different places will be different in its composition.

Soil may contain different proportions of rock particles, clay, and humus.

The soil is classified into three types based on the proportion of particles present in it.

a. Sandy soil

b. Loamy soil

c. Clayey soil

The soil which contains a greater proportion of big particles is called sandy soil.

SANDY SOIL

If the proportion of fine particles present in the soil is higher, it is called clayey soil.

CLAYEY SOIL

If the proportion of large particles and fine particles are almost the same, it is called loamy soil.

LOAMY SOIL

DIFFERENCE BETWEEN SANDY, LOAMY AND CLAYEY SOIL

SANDY SOIL

• The particle size of the soil is large.
• There is a large space between the particles and it cannot fit closely together.
• Sand is well aerated.
• Water can drain quickly through the space between the particles.
• Less water holding capacity.
• Sand is light and dry.

CLAYEY SOIL

• The particle size is very small.
• The soil particles are tightly packed and there is very little space between them.
• Sand is less aerated.
• Water will not drain easily.
• Water holding capacity is more.
• It is heavier as it holds more water.
• It is the best soil for making pots, statues, and toys.

LOAMY SOIL

• Loamy soil is the best soil for the growth of the plants.
• It is a mixture of sand, clay, and silt.
• It has the right amount of humus.
• it has the right water holding capacity.

* SILT- It is the deposit of soil seen at the river bed. The particle size of silt is between sand and clay. It is very fertile as it carries all the minerals from the hills and mountains. it helps in the growth of plants.

PROPERTIES OF SOIL

The important properties that we are going to discuss are the percolation rate of the soil, moisture in the soil, and the water absorption capacity.

PERCOLATION RATE

Have you ever noticed how fast water seeps down through the soil? If you are collecting different samples of soil, the amount of water that seeps down will be different. Why it is so?

The time taken by the water to percolate through a particular sample of soil depends upon the particle size of the soil. We can observe that the time for percolation will be less in the case of sandy soil as it is loosely packed. Water goes down very fast through it.

So percolation rate can be calculated for a particular sample of soil by knowing the amount of water percolated and the time taken for percolation.

Percolation rate (ml/min) = amount of water(ml) /percolation time(min)

If a given sample of soil has taken 10 minutes to percolate 300 ml of water, the percolation rate will be 300/10=30ml/min.

MOISTURE IN SOIL

If you are heating a sample of soil from your garden in a test tube, you can observe tiny droplets of water getting condensed on the inner sides of the test tube. Where does this water come from?

It is due to the moisture or the water content present in the soil.

On a hot summer day, we can observe the air above the hot soil shimmering. The water vapour which is coming out of the soil reflects the sunlight and it appears to shimmer. Hence we can conclude that there is moisture present in the soil.

ABSORPTION OF WATER BY SOIL

Different types of soil will be absorbing water to a different extent.

The amount of water retained by clayey soil will be more than that of sandy soil.

An activity can be performed to observe this. 

Take a funnel and pour a known amount of soil into it. Note down the initial volume of water in a measuring jar and start pouring that into the soil. Make sure that you are pouring it all over the soil. 

Look at the tip of the funnel. When it starts dripping, stop pouring and note down the final volume of water. The difference will give you the volume of water absorbed by the soil.

The percentage of water absorbed by the soil can be found using the equation;

Percentage of water absorbed = U-V/W x100

where U is the initial volume of water in the measuring cylinder, V is the final volume of water in the measuring cylinder and W is the weight of the soil.

SOIL AND CROPS

Wheat and gram - clayey soil and loamy soil which is good at retaining water.

WHEAT

Paddy- clayey soil is rich in clay and organic matter and can retain more water.

PADDY

Lentils and pulses- loamy soil that drains water easily.

Cotton - sandy loam or loamy soil that can drain water easily and are well aerated.

COTTON FARM

In this chapter, you have learned about the formation of soil, soil profile, types of soil, and the properties of soil. You have already studied soil erosion and soil pollution in your geography lessons. The activities that are mentioned in the NCERT textbook can be performed at home to make the concepts more clear. This abstract of soil chapter 9 class 7 notes will definitely help you to enhance your knowledge of this chapter.

physical and chemical changes class 7

PHYSICAL AND CHEMICAL CHANGES - CHAPTER 6- IMPORTANT TOPICS

physical and chemical changes class 7

We are observing different types of changes around us in our daily life. Some changes are taking place very slowly like the growth of your nail or hair. But there are some changes which occur very fast. Certain changes are reversible like melting and freezing of water. Setting curd from milk is a desirable change, but milk getting spoiled is an undesirable change. In this session, we can see another type of classification. They are PHYSICAL CHANGE and CHEMICAL CHANGE.

PHYSICAL CHANGES

A change in which the physical properties of a substance undergoes change is called a physical change.

Normally physical properties like shape, size, state, and color are changed. Most of the physical changes are reversible. During a physical change, new products are not formed.

paper boat

If you are making a paper boat, it can be unfolded to get back the paper in the same shape, size, and color. So it is a physical change.

If you are taking some ice and melting it. water is obtained. To get back ice, we can keep that water in a freezer. Similarly  the steam obtained by boiling water can be condensed back to water. Hence change in state of matter is a physical change

Iron on heating will become red hot and it will get its color back on cooling. This is also an example of physical change. Think about such changes happening around you and make a list of five physical changes.

CHEMICAL CHANGES

In a chemical change, one or more new products are formed. Most of the chemical changes are not reversible. It is also called a chemical reaction, as it leads to the formation of new things.

 

On burning a piece of paper, we can observe the formation of ash. But on tearing a piece of paper, we are not getting any new product. Rusting iron is another example of a chemical change. Iron articles will get rusted when exposed to air. The rust obtained is the new product formed and we cannot get back iron from it.

Chemical changes are accompanied by the following changes:

• color may change
• the sound may be produced
• gas may be evolved
• heat, light or any radiation might be evolved or absorbed
• smell may be changed

More examples of chemical changes/chemical reactions

1. Burning of Magnesium ribbon

Burn a small strip of magnesium ribbon on flame. It burns with Oxygen in the air with a dazzling white light leaving behind white powdery ash.

The reaction can be represented as:

Magnesium + Oxygen → Magnesium oxide

Mg + O2 → MgO

Dissolve the white powder obtained (MgO) with water and test it with red and blue litmus paper.

The red litmus paper will turn blue and there is no color change with blue litmus paper. This indicates the formation of a basic compound.

Magnesium oxide + water → Magnesium hydroxide

MgO + H2O → Mg(OH)2

2. Reaction of Iron and Copper sulphate

Place an iron nail in a Copper sulphate solution that contains a few drops of dilute sulphuric acid. Observe the color change after some time.

We can observe the color change from blue to green and some brown powdery deposits on the iron nails. This is due to the chemical reaction between iron and copper sulphate.

Blue-colored copper sulphate reacts with iron to form green-colored iron sulphate and brown-colored copper.

The reaction is as follows:

Copper sulphate + Iron → Iron sulphate + Copper

copper sulphate

3. Reaction of Acetic acid and Baking soda

Add a pinch of baking soda to acetic acid (vinegar). We can observe the formation of gas bubbles with a hissing sound. The bubbles are due to the formation of carbon dioxide.

Acetic acid + Baking soda → Carbon dioxide + other substances

On passing the gas obtained in the above reaction through lime water (Calcium hydroxide), the colorless solution turns milky.

The reaction is as follows:

Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

Ca(OH)2 + CO2 → CaCO3 + H2O

When carbon dioxide is passed through colorless calcium hydroxide, calcium carbonate is formed which turns milky. This is a standard test of carbon dioxide.

4. Rusting of Iron

When an iron article is exposed to air, it reacts with oxygen and moisture to form hydrated iron oxide (rust). It is represented by the equation:

Iron + Oxygen + Water → Iron oxide

Fe + O2 + H2O → Fe2O3.x H2O

The presence of both oxygen and water is essential for rusting.

If the air is more humid, rusting becomes faster.

Prevention of rusting

Rusting of iron can be prevented:

•   By painting
• By oiling 
•    By greasing
•           By galvanization
•   By alloying

Galvanization- It is the process of depositing a layer of zinc on iron. The iron pipes to carry water and storage tanks are galvanized to prevent rusting.

Alloying-  is the process of mixing different types of metals or metals with non-metals. Stainless steel is made by mixing iron with carbon, chromium, nickel, and manganese.

acids bases and salts class 7 easy study material

ACIDS, BASES AND SALTS CHAPTER-5 GRADE 7-CHEMISTRY

acids bases and salts class 7 notes

In our daily life, we are using many vegetables and fruits which are sour. Have you ever wondered, why these are sour to taste?

Lemon, orange, vinegar, curd-like that many sour things we include in our diet. At the same time, some food items are sweet, bitter, and salty. Let's learn the chemistry behind these.

ACIDS

Substances that are sour to taste contain acids in it. Those substances are acidic in nature. The word acid itself means sour. Fruits and vegetables contain natural acids.

citrus fruits

NATURAL ACIDS-acids which occur in nature. It is also called organic acids.

Acetic acid	vinegar
Formic acid	ant's sting
Citric acid	citrus fruits like lemon, orange, etc.
Lactic acid	curd, buttermilk
Oxalic acid	spinach, tomato
Ascorbic acid   (vitamin C)	citrus fruits, gooseberry
Tartaric acid	tamarind, grapes, unripe mango

MINERAL ACIDS- acids that are made from inorganic minerals. Hence it is also called inorganic acids. Examples are given in the table below.

Hydrochloric acid	HCl
Sulphuric acid	H2SO4
Nitric acid	HNO3
Phosphoric acid	H3PO4

Sulphuric acid is called the King of chemicals.

BASES

There are certain substances that are bitter to taste and soapy to touch. Such substances are called bases. The nature of such substances is basic.

Examples: baking soda, Calcium hydroxide(lime water), Sodium hydroxide, Potassium hydroxide, Magnesium hydroxide

baking soda

INDICATORS

Substances that are used to test whether a given sample is acidic or basic are called indicators.

Indicators can show different colors with an acidic or a basic substance.

Indicators can be of two types:

• Natural indicators- turmeric, litmus solution or litmus paper, china rose petals, red cabbage juice
• Synthetic indicators- phenolphthalein, methyl orange

LITMUS

It is a commonly used indicator. Litmus is extracted from lichens. In distilled water, it has a purple color. It turns red when added to acids and it turns blue when added to bases.

Litmus solution or litmus paper is available for testing. Commonly we are using red litmus paper and blue litmus paper.

On dipping a blue litmus paper in acid, it turns red.

On dipping a red litmus paper in acid, it remains red(no color change).

On dipping a red litmus paper in the base, it turns blue.

On dipping a blue litmus paper in the base, it remains blue(no color change).

lichens

Neutral solutions

Substances that are neither acidic nor basic are called a neutral solution. They do not show any color change with red or blue litmus papers.

Example- distilled water, salt solution, sugar solution

TURMERIC 

turmeric

Turmeric indicator can be made at home by applying a paste of turmeric on a piece of white paper and drying it. When you apply a drop of soap solution on it, it turns red. This indicates that soap is basic.

with acid- yellow color

with base- red color

CHINA ROSE 

China rose (hibiscus)

For making china rose indicator, take some china rose petals and mix it with warm water and keep it aside for some time. The colored solution obtained can be used as an indicator.

With acid- magenta (dark pink)

With base- green

SYNTHETIC INDICATORS

Phenolphthalein- Color change

With acid - colorless

With base - pink

Methyl orange- color change

With acid- red

With base- yellow

NEUTRALISATION

The reaction between an acid and a base to obtain salt and water is called neutralization.

Acid + Base → salt + water

Example: On adding Hydrochloric acid to Sodium hydroxide, Sodium chloride and water are formed. In this Sodium chloride is the salt formed. Heat is also produced during this reaction.

Hydrochloric acid + Sodium hydroxide →Sodium chloride + water

HCl + NaOH →NaCl + H2O

NEUTRALISATION IN EVERYDAY LIFE

                                1. INDIGESTION

antacid-gelucil tab

When we have indigestion problems, we usually take this kind of medicine. The hydrochloric acid present in our stomach helps indigestion. But when there is more amount of this, it causes acidity. 

To reduce acidity, we are taking mild bases like milk of magnesia which contains Magnesium hydroxide. These bases are called antacids and it can neutralize the effect of excess acid and relieve stomach pain.

2. ANT BITE

ant 

When an ant bites our body, it injects formic acid and it causes irritation and pain. 

On rubbing moist baking soda (sodium hydrogen carbonate) or calamine lotion (zinc carbonate), the effect of an acid can be neutralized.

3. SOIL TREATMENT

soil treatment

When the soil is too acidic, we must add bases like quick lime or slaked lime. Organic matter like leaf waste and decayed vegetables are added when the soil is more basic. This way we can neutralize the soil for the better growth of the plant. 

4.FACTORY WASTE

factory waste

The factory wastes are neutralized with bases if they contain more acid in it. If it is disposed directly to the water bodies, it will affect the aquatic life. There should be proper pollution checks in this area to save our natural resources.

fibre to fabric class 7

FIBER TO FABRIC- IMPORTANT TOPICS

ANIMAL FIBERS- WOOL AND SILK

WOOL

Wool is a very popular animal fiber widely used all over the world. It is mainly obtained from sheep. But there is much wool yielding animals like camel, alpaca, llama, goat, yak, etc.

WOOL YIELDING ANIMALS

fiber to fabric class 7

SHEEP

alpaca

ALPACA

llama

LLAMA

yak

YAK

angora goat

ANGORA GOAT

Angora goats are reared in Jammu and Kashmir and are known for their soft and fine fleece.

Pashmina shawls are made from the wool of Kashmiri goat.

pashmina shawl

SELECTIVE BREEDING

In order to get special characters in the offspring, good quality parents are selected for breeding. This selection process of parents is called selective breeding.

Example- sheep with soft under hair are selected for getting good quality wool.

PROCESSING OF FIBRES INTO WOOL

STEP-1- SHEARING

shearing

Shearing is the process of removal of the fleece of sheep along with a thin layer of skin. It is normally done during summer.

STEP-2 -SCOURING  

Scouring is the process of washing the sheared skin with fleece in tanks to remove dirt, dust, and grease. It is usually done by hand or machines.

STEP-3- SORTING

Sorting is done in the factories after scouring, based on its texture.

STEP-4 - REMOVAL OF BURRS

There will be fluffy fibers called burrs on the fleece. Burrs are picked out and the fibers are scoured again and dried. 

STEP-5 - DYEING

dyeing

The natural colors of fleece are white, black, and brown. The fibers can be dyed in different colors.

STEP- 6 - ROLLING

wool roll

The fibers are then straightened, combed, and rolled into yarn for making fabric.

ANTHRAX- SORTER'S DISEASE- Sorters in the wool industry will get affected by a bacterium which causes a fatal blood disease. This kind of disease faced in industries is called an occupational hazard.

SILK

silk

Silk was originated in China and now it is made all around the world.

SERICULTURE- it is the rearing of silkworm for obtaining silk.

sericulture

LIFE HISTORY OF SILK MOTH

eggs

EGGS

silkworms

SILKWORM

cocoons

COCOON

silk moth

SILK MOTH

The female silk moth lays eggs on leaves and then hatch silkworms or caterpillars. Silkworms eat mulberry leaves and grow in size. Then it enters the pupa stage. It swings its head in the form of eight and secretes a liquid that contains protein. It hardens on exposure to air and turns into silk fiber. This covering made is called a cocoon. Inside the cocoon, the pupa will develop into a silk moth.

Examples of silk- Tassar silk, Mooga silk, Kosa silk

PROCESSING OF SILK

• Eggs are stored on cloth or paper and sold to silkworm farmers.
• They keep them under suitable conditions of temperature and humidity
• The eggs are hatched to form silkworms.
• They eat mulberry leaves day and night and grow in size.
• After 25 to 30 days, the silkworms stop eating and move to a tiny chamber of bamboo in the tray to spin cocoons.
• The cocoons are kept under the sun or boiled in water or exposed to steam to separate out silk.
• The silk fibers can be used to make silk threads and are woven into silk cloth by weavers.

REELING- It is the process of taking out silk threads from the cocoon for use as silk.

reeling silk

silk cocoons