class 10 chemistry important question 2020 - chapter1, chapter2 chapter3

class 10 chemistry important question 2020

CHAPTER- 1 CHEMICAL REACTIONS 
PRACTICE QUESTIONS

         1 mark question

1. Why do we store Silver chloride in dark colored bottles?                                 

2.Identify the type of reaction

(a) 2 AgNO₃ + Cu    → Cu (NO₃)₂ + 2 Ag

(b) 2 SO₂ + O₂    →       2 SO₃     

2 marks question                                                                            

3. What change in the colour of iron nail and copper sulphate solution do you observe after keeping the iron nail dipped in copper sulphate solution for about 30 minutes? Write the equation involved.                                                                                

4.Balance the following equations:

(a) Fe + H₂O    →      Fe₃O₄ + H₂

(b)HNO₃+Ca(OH)₂ →Ca(NO₃)₂+H₂O                                                    

5.Identify the substance oxidized, reduced , oxidizing agent and reducing agent:

        MnO₂ + 4 HCl      →    MnCl₂  + 2 H₂O+Cl₂                                                            

6. (a) What is rancidity?

   (b) Write the common methods to prevent it?    

3 marks questions                                                       

7. What happens when aqueous solution of Sodium sulphate and Barium chloride are mixed together? Give a balanced equation for the reaction and write the state symbols. Name and define the type chemical reaction involved in the above change.   

8.  2 g of ferrous sulphate crystals were heated in a hard glass test tube and observations are recorded.

(a) What was the successive color change?

(b) What type of odour is observed?

(c) Name the products obtained.

(d)What type of reaction is this?                                                                                  

 9.What are decomposition reactions? give one example each of

(a) Thermal decomposition

(b) Electrolytic decomposition

(c) photolytic decomposition.  

5 marks questions                                                            

10.Sonia has been collecting silver coins and copper coins. One day she observed a green coating on copper coins and a black coating on silver coin.

     (a) Which chemical phenomenon is responsible for these coating?

     (b) Write the chemical name of black and green coatings.

     (c) Explain with equations involved.                                            

11. A reddish brown metal X on heating in presence of Oxygen forms a black coloured compound Y which is basic in nature and  when heated with Hydrogen gas gives back  X. Identify X and Y. Write the chemical reaction between Y and Hydrogen.Identify the substance being oxidized and reduced.             

                                                      

ACIDS, BASES AND SALTS-CHAPTER 2

1 MARK QUESTIONS

1.What is the name given to the indicators giving different odours in acidic and basic medium.Give one example?   

                                                                                

2. Name the acid present in the bee sting. Write the common method to get relief from the pain and irritation caused by bee sting.   

2 MARKS QUESTIONS

3.What do you see when pentahydrate copper sulphate crystals are heated. Give reasons too?                                                                                                                     

4.Given the pH values of four different liquids as 7,14,10,2.Which of these could be that of, (a) lemon juice, (b)distilled water, (c) NaOH, (d) Milk of magnesia?

  

5. What is baking powder? How does it help the cake to become soft and spongy?   

3 MARKS QUESTIONS

6.Identify the compound of Ca which is used for plastering of fractured bones.Using suitable chemical equation, show how it is prepared and what are the special precautions taken during the preparation of this compound.                            

7.The pH of a salt used to make tasty and crispy pakodas is more than 7.Identify the salt and write a chemical equation for its formation. List its two uses.  

                               

8. Eating too much sweets may lead to tooth decay.How can tooth paste prevent cavities on tooth?                                                                                                       

9.Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved..Identify A,B,and C and write its formula.                                       

5 MARKS QUESTIONS

10.A student dropped few pieces of marble in dilulte HCl,contained in a test tube.The evolved gas was then passed through lime water. What change would be observed in lime water. What will happen if excess of gas is allowed to pass through lime water.Explain the observations with the help of chemical equations for all the changes.  

  

11.(a) Identify the compound of Calcium which is yellowish white powder and is used for disinfecting drinking water.

(b)Write its chemical name and formula.

(c) How is it manufactured?

(d) Write the chemical equation involved in the reaction.

(e)Also list two uses of the compound.                         

 

 

METALS AND NON METALS- CHAPTER-3

metals and non metals extra questions class 10

         1 MARK QUESTIONS

1. A non -metal X can exist in two different forms and they are Y and Z. Y is the hardest natural substance and is very expensive whereas Z is a good conductor of electricity. Identify Y and Z.               

2. Why ionic solids do not conduct electricity?   

3. Name the metals involved in the electrical activity in nerves and muscles.

4. Name the type of oxide formed when non-metals combine with oxygen. 

2 MARK QUESTIONS                                               

5.Show the formation of magnesium chloride by the transfer of electrons?      

6. What are the constituents present in solder alloy? Explain the property of solder which helps us to use it for welding electrical wires?                                                               

7.A metal can exists as a liquid at room temperature

and it is obtained by heating its sulphide form in the presence of air.

(i) Identify the metal and its ore.

(ii)the reactions involved.

8.Explain the terms:

 (a) roasting

 (b) calcination.                                                               

                      

3 MARKS QUESTIONS                                                                                                

9.(a) What are amphoteric oxides? 

Choose the amphoteric oxides amongst the following oxides.

Na₂O, ZnO,  Al₂O₃,  CO₂ ,H₂O

(b) Why  metals do not displace Hydrogen when reacted with dilute Nitric acid?                                   

10. Write the chemical equations for the reactions taking place when:

(i) Zinc sulphide  is heated in air

(ii) Calcination of Zinc carbonate is done

(iii) Magnesium dioxide is heated with Aluminium powder.                               

11. Give reason-

a. Articles which are made up of aluminium do not corrode easily even though aluminium is an active metal.

b.Carbon can not be used for making aluminium from aluminium oxide.

c. Sodium and Potassium are stored in kerosene oil.                                                                                                                                                                           

12.( a) What are alloys?

   (b)What are the alloys called amalgams

  (c) Give two examples of alloys containing copper as one of the constituents.                                                                                          

5 MARKS QUESTIONS                                         

13. (a)What is meant by refining of metals?

(b)Name the most widely used method of refining impure metals produced by various reduction processes.

(c)Describe with the help of a labelled diagram, how this method may be used for refining of Copper. 

14.(a)Name a liquid metal which does not stick to glass.

(b)Name a non metal which is a good conductor of electricity.

(c)Name the metal which is commonly used in thermite welding.            

(d)What gets deposited at the cathode, a pure metal or impure metal?          

(e)What is the nature of ZnO?  

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

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.