NCERT SCIENCE CLASS 6--sorting materials into groups -chapter 4- study material

SORTING MATERIALS INTO GROUPS- CHAPTER 4 -IMPORTANT TOPICS

NCERT SCIENCE CLASS 6--sorting materials into groups -chapter 4- study material

Look at this picture. How nicely the hats are arranged on each shelf! Have you ever wondered why we are sorting and arranging things? What is the need for sorting different materials and which are the criteria for sorting? Is sorting materials into groups makes our task easier?

In this session, we can discuss the sorting of materials into groups based on their properties. The objects we see around us are made up of one or more materials like metal, plastics, glass, wood, mud, etc. You can make a list of materials that are around you and group them according to the material by which it is made up of.

Certain objects that we choose may be using different materials. For example, you may have chairs made up of wood, plastic, or metals at home.

plastic chair

wooden chair

Similarly, we can find that a plate, pen, or cot made of different materials. Make a list of objects and the materials by which each one can be made.

Contrary to this, we can think about a material like wood or plastic and list out objects made by this. For example, using cotton, we can make clothes, bed sheets, bags, curtains, etc. Make a table of items like this and find out five items each.

So we can find that objects around us are made of different materials and one material could be used for making many different objects.

PROPERTIES OF MATERIALS

When we are choosing a material for making an object, we need to consider many things like its availability, properties, cost factor, manufacturing methods, etc. Among this, the most important factor is the properties of the material. If we know the properties, sorting of materials into groups is easy. Some of the properties that are discussed here are appearance, hardness, solubility, floating, and transparency.

(a) Appearance

copper

Materials are always different in their appearance and we can make out it from its texture and luster. Metal looks different from wood. Metals like gold, silver iron, copper, etc are lustrous. On exposure to air for a long period of time, iron and copper may become dull. But when it is freshly cut, it shines.

(b) Hardness

Certain objects around you can be compressed easily whereas other objects are difficult to compress. A sponge is easily compressible. You can make a mark on wood with an iron nail by scratching on it. That means iron nail is more hard than wood.

Materials that can be compressed or scratched easily are called soft material and materials which are not easy to compress are called hard materials.

soft sponge

hard rock

    (c) Solubility

You might have noticed that some of the objects dissolve completely in water and some of them do not dissolve. This is one of the important properties for sorting materials into groups. On dissolving salt or sugar in water, it gets soluble easily. If you are adding and mixing chalk powder in water, it may not be dissolving completely.

The substances that are completely dissolving are called soluble substances. Substances that do not mix with water and do not dissolve even after stirring are called insoluble substances.

Solubility is applicable to liquids and gases also. On mixing water and vinegar, it is easily miscible. But on mixing oil and water, we will get two separate layers. Some gases like oxygen are soluble in water. We know that aquatic living things are depending on dissolved oxygen in the water.

fish need oxygen

   (d) Floatation

ice floating

We have seen ice floating on water. Depending on the density, objects can float or sink. The object which is less dense will float. Ice is less dense than water. Similarly, a dry leaf thrown into a pond floats in water, while a stone sinks. When a few drops of honey are poured into a glass of water, it sinks.

 (e) Transparency

transparent glass

Can you see through these glass tumblers? Yes, they are transparent. Substances or materials through which things can be seen are called transparent materials. In our daily life, we come across many transparent materials.

frosted glass

When we are looking through frosted glass, we can not the other side clearly. It allows the light to pass through it partially. Such materials through which objects can be seen partially, not clearly are called translucent. You can think about more examples of this.

wooden plank

Are you able to see the other side when you look through these wooden logs? The materials like wood and metals will not allow the light to pass through it. Hence we can not see the other side. These materials are called opaque materials. List out more examples of opaque objects.

 So we can sort different materials into different groups based on the similarity of their properties. Grouping or sorting is done for our convenience. In shops, libraries, textile,s and even at home, we store different things by sorting things for our easy access. Grouping or sorting of materials into groups is helpful to study the properties of groups and to observe the pattern in these properties.

changes around us class 6

 CHANGES AROUND US

Have you observed nature? Can you list out some changes that are happening around you?

We can see the change in season, growth of a plant from a sapling, boiling water, flowers blooming, and many more like that when you observe.We need to classify the changes into different groups.

changes around us class 6

melting of ice

boiling water

Some changes happen very slowly and some are fast. The growth of a plant is a slow change, but the burning of a paper is fast change. Some changes are desirable and some are not. Milk changing to curd is desirable, but milk getting spoiled is undesirable.  Some changes can be reversed and some cannot be reversed. Many changes are physical changes and many are chemical changes.

REVERSIBLE AND IRREVERSIBLE CHANGES

balloons

A balloon changes its size and shape on blowing air into it. If you let the air escape, it will come back into its original shape. Hence it is a reversible change.

Similarly, on unfolding a paper boat, we will get the paper in the same shape and size.

paper boat

If you take an ice cube and melt it, how will you get it back? We can bring it back by freezing. The same is the case with boiling water. Evaporated water vapor will condense back to the water. Hence all these changes are examples of reversible changes.

Let's see a few more changes.

dough

Make a ball with the dough and roll out a roti. Maybe you are not happy with its shape. We can bring it back to the ball of dough. This is a reversible change. But if you are baking the roti on a pan, are you able to get back the dough again? So the second one is not a reversible change. We can observe many irreversible changes in our daily life. 
Change of milk to curd, boiling of an egg, burning of paper, growth of a plant- these are all irreversible changes.
A change in which we can get back the same material in the same state is called a reversible change.
A change in which material changes into another form and cannot be brought back is called an irreversible change.

WAYS TO BRING A CHANGE

1. By heating

2. By cooling

3. By burning

4. By adding other things

blacksmith making tools

In the picture, you can see how a blacksmith makes a tool. He uses the principle of expansion and contraction to fix the handles of these tools. On heating, the metal expands, and on cooling, it contracts.

burning candle

We have observed the burning of a candle. Do you get the same amount of wax when it burns? The length of the candle decreases as it burns and it forms water vapor and carbon dioxide which are gases and it escapes into the atmosphere. Hence burning of a candle is an irreversible change. 
But on melting a piece of wax, we can bring it back by cooling. So melting of wax is a reversible change.
On adding a spoon of salt to the water, the dissolved salt can be obtained by evaporating water.
There must be many other ways of changing things around us. So we have discussed changes that can be reversed and change that cannot be reversed.

separation of substances class 6

SEPARATION OF SUBSTANCES-CLASS 6-IMPORTANT TOPICS

separation of substances class 6

In our daily life, there are many instances to separate different substances from a mixture.

We need to separate harmful or non-useful substances. Sometimes, we separate even useful components if we need to use them separately. Different separation methods are used depending upon its state, size, miscibility, etc.

We shall discuss some of the important methods here.

1. HANDPICKING

The method of handpicking is done for separating components having a difference in size. The quantity of substances to be separated should be less.

Example: stones from rice or pulses, husk from wheat.

2. THRESHING

threshing

We can separate the grain from stalks by threshing. By the threshing process, stalks are beaten on a hard surface to free the grains. Bullocks and machines are also used to thresh large quantities of grain.

3.WINNOWING

winnowing

winnowing

Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. Wind manages to separate heavier particles from lighter particles.

We can see winnowing in our paddy fields, where farmers separate lighter husk particles from heavier seeds of grain.

4. SIEVING

sieving

Sieving is done if components of a mixture have different sizes. Smaller particles are allowed to pass through the holes of the sieve while bigger particles will remain on the sieve.

Example: impurities and bran present in flour are removed by sieving, pebbles and stones are removed from sand using sieve at construction sites.

5. SEDIMENTATION, DECANTATION, FILTRATION

filtration

Have you tasted filtered coffee? This is how it is made by the process of filtering.

• Fine insoluble impurities can be removed from liquids by the process of sedimentation, decantation, and filtration.

• When the heavier components in a mixture of solid and liquid settle down at the bottom, that process is called sedimentation.

• 

  sedimentation
  

• The process of pouring out a clear solution from the top of the mixture after sedimentation is called decantation. 

• The remaining very fine particles can be removed by filtration using a filter paper as shown in the picture. 

• A filter paper has very fine pores and the solid particles in the mixture do not pass through it and remain on the paper.

Example: Mud particles from muddy water can be removed using filter paper.
Cottage cheese or paneer (in Hindi) is filtered through a fine cloth or a strainer.
A similar principle is used for separating a mixture of two liquids that do not mix with each other. For example, oil and water mixture can be allowed to stand for some time to get two separate layers. Then it can be separated by using a separating funnel as shown in the picture.

separating funnel

6. EVAPORATION

salt field

I

In this picture, you can see how salt is made from seawater by evaporation in salt fields. To separate water and salt, seawater is evaporated by the heat of the sun. In a few days, the water evaporates completely leaving behind the solid salt. Common salt is then obtained from this after purification.

The process of conversion of liquid into its vapor state is called evaporation.

 CONDENSATION - The process of conversion of any vapor into its liquid form is called condensation. 

We use evaporation and condensation together in the separation of certain mixtures.

 SATURATED AND UNSATURATED SOLUTION

A solution in which no more soluble substance can be dissolved is called a saturated solution.

Example: on adding more salt to the water , it remains undissolved and settles at the bottom. It is a saturated salt solution. A larger quantity of salt can be dissolved on heating. Heating increases the solubility.

If we can add more salt to a solution and if it is getting dissolved completely, it is an unsaturated solution.

  

Here we have discussed a few methods of separation methods only. In higher grades, you will learn more techniques of separation.

fibre to fabric class 6

FIBRE TO FABRIC -IMPORTANT TOPICS TO LEARN

fibre to fabric class 6

            

fabric

FIBRE →YARN → FABRIC

cotton fibre

↓

yarn

↓

fabric

Fabrics are made up of yarns and yarns are made up of fibres.

Fibres are classified into two types:

*Natural fibres

   *Synthetic fibres

Examples of natural fibres- cotton, wool, silk, jute (obtained from plants and animals)

Examples of synthetic fibres - nylon, polyester, acrylic (man-made)

LET'S SEE HOW SOME PLANT FIBRES ARE MADE.

COTTON

Where does this cotton come from? Cotton is grown in fields and black soil is the best soil for cotton cultivation. They grow well in a warm climate. Fruit of the cotton plants is called cotton bolls. When the bolls burst open on maturing, it is collected. Fibres can be separated from the seeds by combing.

Ginning- the process of separating fibres from the seeds of cotton bolls is called ginning. It is done traditionally by hand and nowadays by machines.

cotton field

cotton bolls

SPINNING OF COTTON YARN

We can make yarn from fibres.

Fibres from a mass of cotton are drawn out and twisted to make a yarn. This process is called spinning.

The device used for spinning is a hand spindle (takli in Hindi) and another device used is Charkha (Hindi) which was popularized by Mahatma Gandhi. On a large scale, spinning is done by spinning machines.

spinning

YARN TO FABRIC

The main processes to make fabric from yarn are 

WEAVING and KNITTING.

WEAVING-The process of arranging two sets of yarns together to make a fabric is called weaving. It is done on looms which are hand-operated or power operated.

loom

loom

KNITTING - In knitting, a single yarn is used to make a fabric. Loops are made with yarn using knitting needles. It is done by hand or on machines. Sweaters and socks are made by knitting.

knitting

knitted sweater

knitted socks

      JUTE

jute yarn

• The fibre of jute is obtained from the stem of the jute plant.
• It is cultivated during the rainy season.
• It is harvested when it is at its flowering stage.
• The stems of the jute plants are immersed in water for a few days.
• The stems rot and fibres are separated from the stalks by a to and fro motion in water.
• The fibres are hung on bamboo railings for sun drying for 2-3 days.
• Then jute fibres are sold in the market for making different products like jute bags, fabrics, sacks etc.

jute farm

 

jute sacks

In this topic, you have learnt about different types of fibres and the production of plant fibres like cotton and jute. In higher grades you will learn about animal fibres like silk and wool.certain synthetic fibres and its uses are also there to enrich your knowledge about fibres and fabric.