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Showing posts with label NCERT Science. Show all posts
Showing posts with label NCERT Science. Show all posts

Is Matter around us Pure (Class - 9th) Exercise , Question and Answer (NCERT Book)

Chapter – 2

Is Matter Around Us Pure

 

 

Question 1. Which separation techniques will you apply for the separation of the following?

 

(a) Sodium chloride from its solution in water.

-------Evaporation.

 

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.

-------Sublimation

 

(c) Small pieces of metal in the engine oil of a car.

------Filtration

 

(d) Different pigments from an extract of flower petals.

-------Chromatography

 

 

(e) Butter from curd.

------------Centrifugation

 

(f) Oil from water.

---------Separating Funnrl

 

(g) Tea leaves from tea.

---------Filtration

 

(h) Iron pins from sand.

-------------Magnetic Separation

 

(i) Wheat grains from husk.

------------ Sieving

 

(j) Fine mud particles suspended in water.

--------- sedimentation and then filtration.

 

 


Question 2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Ans – First water is taken as a solvent in a sauce pan. This water is allowed to boil. During heating , milk and tea leaves are added to the solvent as solutes. They form a solution. Then the solution is poured through a strainer. The insoluble part of the solution remains on the strainer as residue. Sugar is added to the filtrate, which dissolved in the filtrate. The resukting solution is the required tea.

 

Question 3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

Substance Dissolved

Temperature in K

283

293

313

333

353

Potassium nitrate

21

32

62

106

167

Sodium chloride

36

36

36

37

37

Potassium chloride

35

35

40

46

54

Ammonium chloride

24

37

41

55

66

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

Ans – At 313 K the mass of potassium nitrate dissolved in 100g of water is 62 g.

At 313 K the mass of potassium nitrate dissolved in 50 g of water = 62g/100 X 50g = 31 g.

 

 

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.

Ans – On cooling the solution at room temperature the crystals of potassium chloride will be obtained.

 

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

Ans – Solubility at 293 K.

(i)              potassium nitrate = 32 g per 100 g of water.

(ii)           Sodium chloride = 36 g per 100 g of water.

(iii)        Potassium chloride = 35 g per 100 g of water.

(iv)         Ammonium chloride = 37 g per 100 g of water.

This shows that the ammonium chloride has the maximum solubility at 293 K.

 

(d) What is the effect of change of temperature on the solubility of a salt?

Ans – With  increase in temperature the solubility of all salts in water increases and when temperature is decreased the solubility of these salts in water decreases.

Question 4. Explain the following giving examples.

(a) Saturated solution – A saturated solution is a solution in which the maximum amount of solute has been dissolved at a given temperature. The solution cannot dissolve beyond that amount of solute at that temperature. Any more solute added will settle down at the bottom of the container as a precipitate.

 

(b) Pure substance – A pure substance is a substance consisting of a single type of particles, i.e. all constituent particles of the substance have the same chemical properties.

For example – salt , sugar, water are pure substances.

 

(c) Colloid – A colloid is a heterogeneous mixture. The size of the solutes in this mixture is so small that they cannot be seen individually with naked eyes, and seems to be distributed uniformly throughout the mixture. The solute particles do not settle down when thw mixture is left undistributed. Colloids show Tyndall effect. For example – milk, butter, foam , fog, smoke, clouds.

 

(d) Suspension – Suspension are heterogeneous mixture. The solute particles in this mixture remain suspended throughout the bulk of the medium. The particles can be seen with naked eyes. Suspension shows the Tyndall effect. The solute particles settle down when the mixture is left undisturbed. For example – mixture of chalk powder and water, wheat flour and water.

 

 

Question 5. Classify each of the following as a homogeneous or heterogeneous mixture.

soda water, wood, air, soil, vinegar, filtered tea.

Ans – Homogeneous mixture – Soda water, air, vinegar, filtered tea.

          Heterogeneous mixture – wood, soil.

 

Question 6. How would you confirm that a colourless liquid given to you is pure water?

Ans – Every liquid has a characteristic boiling point. Pure water has a boiling point of 100oC at 1 atmospheric pressure. If the given colourless liquid boils at even slight above or below 100oC , then the given liquid is not pure water. It must boil at sharp 100oC.

 

Question 7. Which of the following materials fall in the category of a “pure substance”?

 (a) Ice

(b) Milk

(c) Iron

(d) Hydrochloric acid

(e) Calcium oxide

(f)  Mercury

(g)  Brick

(h) Wood

(i) Air.

Ans – Pure substance –

(a) Ice                             (b) Iron                        (c) Hydrochloric acid

(d) Calcium oxide                 (e) Mercury        

 

Question 8. Identify the solutions among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water.

Ans – The following mixture are solutions –

(b) Sea water                (c) Air                           (e) Soda water

 

Question 9. Which of the following will show “Tyndall effect”?

 

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution.

Ans – Milk and Starch solution will show “Tyndall Effect”.

 

 

Question 10. Classify the following into elements, compounds and mixtures.

 

(a) Sodium

(b) Soil

(c) Sugar solution

(d) Silver

(e) Calcium carbonate

(f) Tin

(g) Silicon

(h) Coal

(i) Air

(j) Soap

(k) Methane

(l) Carbon dioxide

(m) Blood

Ans – Elements –

(a) Sodium                   (d) Silver             (f) Tin

(g) Silicon

Compounds –

(e) Calcium carbonate           (k) Methane                  (l) Carbon dioxide

Mixture –

(b) Soil                (c) Sugar solution                  (h) Coal

(i) Air                            (j) Soap                         (m) Blood.

 

Question 11. Which of the following are chemical changes?

 

(a) Growth of a plant

(b) Rusting of iron

(c) Mixing of iron filings and sand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of a candle.

Ans – The following changes are chemical changes –

(a) Growth of a plant            (b) Rusting of Iron

(d) Cooking of food              (e) Digestion of food

(e) Burning of candle.

 


Chapter 1 : Matter in Our Surroundings : Class - 9 : Question and Answer (Part -3)

 

NCERT BOOK QUESTIONS AND EXERCISES

Chapter 1 : Matter in Our Surroundings

Part – 3 


Question 1- Convert the following temperature to the Celsius scale :     

      (a)                      293 K              (b) 470 K

 Answer – (a) Temp. On Kelvin scale = Temp. on Celsius scale + 273

293 = temperature on Celsius scale + 273

So, temperature on Celsius scale = 293 – 27

     = 20oC

(b) Temp. On Kelvin scale = Temp. on Celsius scale + 273

470 = temperature on Celsius scale + 273

So, temperature on Celsius scale = 470 – 273

       = 197oC

 

Question 2 – Convert the following temperature to the Kelvin scale -      (a)                      25oC        (b) 373oC

Answer – (a) Temperature  On Kelvin scale = Temperature on Celsius scale + 273 

   = 25 + 273 

  = 298 K

(b) Temperature  On Kelvin scale = Temperature on Celsius scale + 273

      = 373 + 273

     = 646 K

 

Question 3 – Give reasons for the following observations –

(a) Naphthalene balls disappear with time without leaving any solid.

(b)   We can get the smell of perfume sitting several metres away.

Answer –

(a) Naphthalene is a volatile solid organic compound which can undergo sublimation (change from solid states directly in to vapour state). The solid naphthalene balls keep subliming slowly. After a certain time, the naphthalene balls sublime completely forming naphthalene vapours and hence they disappear without leaving any solid residue.

 

(b) We can get the smell of perfume sitting several metres away due to the diffusion of perfume vapours into air. This can be explained as follows : Perfume is a volatile liquid. When liquid perfume is applied by a person, it quickly changes in to vapours. The perfume vapours move very rapidly in all directions in air, mix up with air particles and spread in the air by diffusion. When this air containing perfume vapours reaches several metres away, we can smell the perfume.

 

Question 4 – Arrange the following substances in increasing order of forces of attraction between the particles – water, sugar, oxygen.

Answer – The forces of attraction between the particles in a solid are the strongest, in liquids are less strong whereas in gases are the weakest. Now out of water sugar and oxygen :

(i) Oxygen is a gas, so it has the weakest forces of attraction between its particles.

(ii) Water is a liquid, so it has a stronger forces of attraction between its particles.

(iii) Sugar is a solid, so it has the strongest forces of attraction between its particles.

Thus, the increasing order of forces of attraction between the particles of water, sugar and oxygen will be :

           oxygen < water < sugar

 

Question 5 – What is the physical state of water at :

(a)  25oC         (b) 0oC        (c) 100oC

Answer – (a) The physical state of water at 25oC is liquid.


(b) 0oC is the melting point of ice as well as the freezing point of water. So, the physical state of water at 0oC can be either a solid or liquid.


(c) 100oC is the boiling point of water as well as the condensation temperature of steam. So, the physical state of water at 100oC can be either a liquid or a gas.

 

Question 6 – Give two reasons to justify : 

(a) Water at room temperature is a liquid.

(b) An iron almirah is a solid at room temperature.

Answer – (a) The two general properties of liquids are that liquids have a fixed volume but no fixed shape. Now water is a liquid at room temperature because :

(i)              Water has a fixed volume.

(ii)           Water has no fixed shape.

 

(b)The two general properties of solids are that solids have a fixed shape and a fixed volume. An almirah is a solid at room temperature because :

    (i) an almirah has a fixed shape.

   (ii) an almirah has a fixed volume.

 

Question 7 – Why is ice at 273K more effective in cooling than water at the same temperature?

Answer – First of all please note that the temperature of 273K is equal to 0oC and it is the melting point of ice at the same temperature. Another point to be noted is that the latent heat of melting of ice is 3.34 x 105 joules per kilogram. Now ice at 273K is more effective in cooling a substance than water at the same temperature of 273 K because for melting each kilogram of ice takes 3.34 x 105 joules of its latent heat from that substance and hence cools the substance more effectively. On the other hand, water at the same temperature of 273K cannot take away any such latent heat from the substance and hence does not cool it more effectively.

 

Question 8 – What produces more severe burns – boiling water or steam ?

Answer – When water changes in to steam at its boiling point, it absorbs latent heat of vaporisation. This means that steam at 100oC contains much more heat than boiling water at same temperature of 100oC. So, when steam falls on our skin and condenses to form water, it gives out 22.5 x 105 joules per kilogram of more heat than boiling water at the same temperature. Since steam gives out more heat than boiling water, it cause more severe burns.

 

Question 9 – Name A, B, C, D, E, and F in the following diagram showing changes in state : 

 


 

Answer –

(i) In process A , a solid is changing into a liquid, so A is melting.

(ii) In process B, a liquid is changing in to a gas, so B is vaporisation.

(iii) In process C, a gas is changing into a liquid, so C is condensation.

(iv) In process D, a liquid is changing in to a solid, so D is freezing.

(v) In process E, a solid is directly changing into a gas, So E is sublimation.

(vi) In process F, a gas is changing directly into a solid, so F is also sublimation.

 

Chapter 1 : Matter in Our Surroundings : Class - 9 : Question and Answer (Part -2)

 

NCERT BOOK QUESTIONS AND EXERCISES

Chapter 1 : Matter in Our Surroundings

Part – 2

Question 9 . Convert to following temperature to Celsius scale :

(a)           300 K                          (b)    573 K

Answer : (a) We know that :

Temperature on Celsius  scale = temperature on Kelvin  scale – 273

                                        = 300 – 273

                                        = 27oC

(b)          We know that :

Temperature on Celsius  scale = temperature on Kelvin  scale – 273

                                        = 573 – 273

                                        = 300oC

 



Question 10 : What is the physical state of water at :

(a)          250oC                          (b) 100oC

 

Answer : (a) The boiling point of water is 100oC. So, the physical state of water at a temperature of 250oC (which is much above its boiling point) will be gaseous state.

(b)          The physical state of water at its boiling point temperature of 100oC will be both ‘liquid state’ as well as ‘gaseous state’. This is because at its boiling point the liquid state of water starts changing in to its gaseous state(steam).

 



Question 11 : For any substance, why does the temperature remain constant during the change of state ?


Answer : The heat energy supplied to a substance during the change of state (at its melting point or boiling point ) is all used up in overcoming the force of attraction between its particles without increasing its kinetic energy. Since the heat supplied during the change of state does not increase the kinetic energy of the substance, therefore no rise in temperature takes place. The temperature remains constant.

 



Question 12 : Suggest a method to liquefy atmospheric gases ?

 

Answer : Atmospheric gases can be liquefied by applying pressure and lowering temperature. When enough pressure is applied, the gases are highly compressed in to a small volume. The particles of gases get so close together that they start attracting one another sufficiently to form a liquid. When a gas is compressed too much  by applying high pressure, a lot of heat is produced. So while applying pressure to liquefy gases, it is necessary to lower their temperature to take away the heat produced during compression. 

 

 

Question 13. Why does a desert cooler cool better on a hot dry day?


Answer – The cooling in a desert room cooler is caused by the evaporation of water. A desert cooler cools better on a hot and dry day because the higher temperature on a hot day increases the rate of evaporation of water, and the dryness of air (low humidity of air) also increases the rate of evaporation of water. And due to increased rate of evaporation of water, a desert room cooler cools better on a hot and dry day.

 



Question 14 – How does the water kept in an earthen pot (matka) become cool during summer?


Answer – The earthen pot has a large number of extremely small pores in its walls. Some of the water kept in the earthen pot continuously keeps seeping through these pores to the outside of the pot. This water evaporates continuously by taking the latent heat of vaporisation from the earthen pot and the remaining water. In this way the earthen pot and remaining water lose heat and get cooled.

 



Question 15 – Why does our palm feel cold when we put some acetone or perfume on it ?

Answer – Acetone, petrol and perfume are volatile liquids. When we put some acetone, petrol or perfume on our palm, the acetone, petrol or perfume evaporate rapidly and our palm feels cold. This is due to the fact that to change from the liquid to the vapour state, acetone, petrol or perfume require latent heat of vaporisation. The acetone, petrol or perfume take this latent heat of vaporisation from our palm. The palm loses heat and feels cold.

 



Question 16 – Why are we able to sip hot tea or milk faster from a saucer than a cup ?


Answer – If the hot tea or milk is taken in a cup then due to the narrow shape of the cup, the surface area of hot area or milk in the cup is comparatively small. Because of small surface area the evaporation of hot tea or milk taken in the cup is slow, cooling caused by evaporation is less, and hence the hot tea or milk remains appreciably hot for a much longer time, making it difficult to sip. On the other hand, saucer has a large surface area. Due to the large surface  area of hot tea or milk taken in the saucer, the evaporation of hot tea or milk from the saucer is faster. The faster evaporation cools the hot tea, or milk much more quickly making it convenient to sip.



 

Question 17 – What type of clothes should we wear in summer ?


Answer – We should wear cotton clothes in hot summer days to keep us cool and comfortable. This is due to the following reason : During hot summer days, we perspire more(give out more sweat through the pores of the skin). Sweat (pasina) is mainly water. The cotton clothes are good absorber of sweat. So, cotton clothes absorb the sweat produced on our skin quickly and expose it to the atmosphere for evaporation. The evaporation of sweat from cotton clothes takes the latent heat of vaporisation from our skin. In this way, our skin loses heat and makes us feel cool and comfortable.


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Microrganisms : Friend and Foe (Class - 8) NCERT Science Sollution

Class – 8

Subject – Science

Chapter – 2 : Microorganisms : Friends and Foe

Exercise   (Question and Answer)

 

Question 1. Fill in the blanks.

(a) Microorganisms can be  seen with the help of a _microscope_.

(b) Blue green algae  fix _nitrogen_ directly from air and enhance fertility of soil.

(c) Alcohol is produced with the help of _yeast_.

(d) Cholera is  caused by _bacteria_.

 

Question 2. Tick the correct answer.

(a) Yeast  is used in the production of

(i) sugar                                    (ii) alcohol

 (iii) hydrochloric acid           (iv) oxygen

 

Answer - (ii) Yeast

 

(b) The following is an  antibiotic

(i) Sodium bicarbonate.   (ii) Streptomycin (iii) Alcohol.                        (iv) Yeast

 

Answer - (ii) Streptomycin

 

 

(c) Carrier of malaria-causing protozoan is

(i) female  Anopheles  mosquito (ii) cockroach

(iii) housefly                                  (iv) butterfly

 

Answer - (i) female Anopheles mosquito

 

(d) The most  common carrier of communicable diseases is

(i) ant                                 (ii) housefly

(iii) dragonfly                   (iv) spider

 

Answer - (ii) housefly.

 

 

(e) The bread or  idli  dough  rises because of

(i) heat.                                        (ii) grinding

(iii) growth of  yeast cells.      (iv) kneading

 

Answer - (iii) growth of yeast

 

 

(f) The process of conversion of  sugar into alcohol is called

(i) nitrogen fixation.          (ii) moulding 

(iii) fermentation               (iv) infection

 

Answer - (iii) fermentation

 

 

Question 3. Match the organisms in Column  A  with their action in Column  B.

 

Answer -

Column  A 

Column  B

Bacteria

Causing Cholera

Rhizobium

Fixing Nitrogen

Lactobacillus

Setting of curd

Yeast

Baking of bread

A protozoan

Causing Malaria

A Virus

Causing AIDS

 

 

 

 

 

Question 4. Can microorganisms  be seen with the naked eye? If not, how can  they be seen?

 

Answer - No , microorganisms can not be seen with naked eyes. They can be seen with the help of microscope.

 

Question 5. What are the major groups of  microorganisms?

 

Answer - The major group of microorganisms are as follows -

1. Viruses

2. Bacteria

3. Algea

4. Fungi

5. Protozoa

 

 

Question 6. Name the microorganisms which can fix atmospheric nitrogen  in the soil.

 

Answer - The microorganism which can fix atmospheric nitrogen in the soil is Cyanobacteria (blue green algae).

 

 

Question 7. Write 10 lines on the usefulness  of microorganisms in our lives.

 

Answer - (i) Micro-organisms are used in the making of curd.

(ii) Microorganisms are used in the making of  bread and cake.

(iii) Micro-organisms are used in the production of alcohol.

(iv) Microorgamisms are used in the synthesis of acetic acid (vinegar).

(v) Micro-organisms are used in the preparation of medicines (or drugs) called antibiotics.

(vi) Micro-organisms are used in agriculture to increase the fertility of soil by fixing atmospheric nitrogen gas (to form nitrogen compounds).

(vii) microorganisms are used in the manufacturing of vaccine. ex- corona vaccine.

(viii) Micro-organisms clean up the environment by decomposing the organic matter of dead plants, dead animals and animal wastes into harmless and useful simple substances. 

(ix) Some microorganisms like blue green algea produce oxygen in the process of photosynthesis.

(x) Some Algae and Fungi are used as food. 

 

 

Question 8.  Write a short paragraph on the harmful effects of microorganisms.

 

Answer - Micro-organisms can be harmful in many ways. For example, some of the micro-organisms cause diseases in human beings, other animals and plants. Those micro-organisms which cause diseases are called pathogens. Thus, pathogens are disease-causing micro-organisms. Pathogens can be bacteria, viruses, protozoa or fungi, etc. Micro-organisms cause diseases such as tuberculosis (TB), tetanus, diphtheria, whooping cough, cholera, typhoid, AIDS, food poisoning, malaria, smallpox and chickenpox, etc. Some micro-organisms spoil food, clothing and leather objects. 

 

Question 9. What are antibiotics? What precautions must be taken while taking antibiotics?

 

Answer - A medicine which stops the growth of, or kills the disease-causing micro-organisms is called an antibiotic. The source of antibiotic medicines are micro-organisms. 

Some of the precautions to be observed in the use of antibiotics are as follows :

(i) Antibiotics should be taken only on the advice of a qualified doctor.

(ii) A person must complete the ‘full course’ of antibiotics prescribed by the doctor.

(iii) The antibiotics should be taken in proper doses as advised by the doctor. If a person takes antibiotics in wrong doses (or when not needed), it may make the antibiotics less effective when the person might need it in future.

(iv) Antibiotics should not be taken unnecessarily. Antibiotics taken unnecessarily may kill the useful bacteria in the body and harm us.