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Class 9 Science NCERT solutions of chapter 2-Is matter around us pure
NCERT Solutions of class 9 science chapter 2-Is matter around us pure? are explained here beautifully by an expert teacher of science. What is the importance of the NCERT solutions of the chapter 2-Is matter around us pure?,Its answer is that all NCERT solutions of the chapter 2-Is matter around us pure? delivers you the preliminary knowledge whatever is required to a chemist or scientists for proceeding their experiments or productions. All NCERT solutions are of the questions mentioned within the pages or of back exercise of class 9 science NCERT textbook of class 9. The NCERT solutions of class 9 science chapter 2-Is matter around us pure? are prepared for helping you in your homework and preparation of forthcoming class tests and exams.
NCERT solutions of class 9 science chapter 2 -Is matter around us pure?
NCERT solutions of class 9 science chapter 2 -Is matter around us pure?
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Q1-What is meant by a substance?
Ans-Substance is the pure form of matter, its particles are of the same kinds, as for example hydrogen, iron, water, etc.
Q2-List the points of differences between homogeneous and heterogeneous mixtures.
Ans- Homogeneous mixture- In this mixture one substance is completely dissolved in another substance, its particles are too small to be seen by naked eyes, it passes the beam of light through it, its examples are the solution of sugar and water, air, alloy, etc.
Heterogeneous mixture- In this mixture one substance does not dissolve in another substance completely, its particles are larger. It is of two kinds.
(a)Suspension – Its particles are larger enough that could be seen by naked eyes means these particles are capable to reflect light, its particles are not suspended throughout the mixture, it is not stable and after some time its particle settled down at the bottom. Its examples are soil and water mixture, oil and water mixture, etc.
(b)Colloid-Its particles are smaller than the particles of suspension but larger than the size of the solution. It is a heterogeneous mixture but it looks like a homogeneous mixture. If a beam of light is allowed to pass through it, it is visible which is known as the Tyndall effect. Its examples are milk, mud, etc.
Q3-Differentiate between homogenous and heterogeneous mixtures with examples.
Ans-
| Homogenous mixture | Heterogeneous mixture |
| Particles are uniformly distributed throughout the mixture | All particles are not mixed completely and thus not distributed throughout the mixture. |
| Has uniform composition | Irregular composition |
| The mixture is in the same phase | It can be made of two or more phases separated by two layers. |
Q4-How are sol, solution, and suspension different from each other?
Ans-
| Sol | Solution | Suspension |
| Heterogenous | Homogenous | Heterogenous |
| Particle size 10-7 mm – 10-5 mm | Particle size less than 10-9 mm | Particle size more than 10-7 mm
|
| Tyndall effect is shown | Tyndall effect is not shown | Tyndall effect may be seen or may not be seen, it depends on the particle size. |
| It looks like a homogenous mixture but actually it is heterogenous | It is always transparent | It is opaque |
| Its particles can be seen by an ultramicroscope | Its particles can’t be seen by any device | Its particles can be seen by naked eyes. |
| It diffuses very slowly | Diffuses very rapidly | Don’t diffuse |
| Stable moderately | Stable highly | It is unstable |
| Can settle down with the help of centrifugation | Can not settle down | Settle down automatically |
| Example: Milk, blood, cloud, mud etc. | The mixture of salt-water, sugar-water etc. | The mixture of Air and dust, water and soil etc. |
Q5-To make a saturated solution. 30 gm of sodium chloride is dissolved in 100 gm of water at 293 K. Find its concentration at this temperature.
Ans- Conc. Of sodium chloride
= (Mass of sodium chloride/mass of solution) x 100
Mass of sodium chloride = 30 gm
Mass of solution = Mass of sodium chloride +mass of water
= 30 + 100 =130 gm
Concentration of sodium chloride = (30/130)×100= 23 %
Q6-How will you separate a mixture containing kerosene and petrol(difference in their boiling points is more than 250c), which are miscible with each other?
Ans-Taking the mixture of kerosene and petrol in a distillation flask and fit it with a thermometer. Arranging the apparatus as shown in the fig.
Heating the mixture and observing the reading at the thermometer. The kerosene vaporizes and condenses in the condenser and can be collected from the condenser outlet and petrol is left behind in the flask. This process of separating the mixture is known as distillation.
Q7-Name the technique to separate
(i) Butter from curd
(ii)Salt from sea-water
(iii) Camphor from salt
Ans- (i) Butter from curd is separated by the method of centrifugation. In this method curd is made to spin rapidly, the havier particles of butter are forced to bottom and lighter particles of buttermilk stay at the top.
(ii) Salt is separated from seawater by the method of evaporation, In this method, seawater is heated in a container due to this water is evaporated leaving behind salt.
(iii) Camphor is separated by the method of sublimation, there are few substances that directly change from solid-state to gaseous state or gaseous state to solid-state, such a process is known as sublimation. In this method when the mixture of salt and camphor is heated the camphor changes into gas leaving behind the salt alone.
Q8-What type of mixtures are separated by the technique of crystallization?
Ans- Few substances get crystallized from their solution, this method is used to purify solid which contains impurities in it. As an example salt from seawater has many impurities. Salt gets crystallized and separated from all the impurities when its solution is dried.
Q9-Classify the following as chemical or physical changes:
- Cutting of trees
- Melting of butter in a pan.
- Rusting of almirah
- Boiling of water to form steam.
- Passing of electric current through water and the water breaking down into hydrogen and oxygen gases.
- Dissolving common salt in water.
- Making a fruit salad with raw fruits and
- Burning of paper and wood
Ans-
- Physical change
- Physical change
- Physical change
- Chemical change
- Chemical change
- Physical change
- Chemical change
Q10-Try segregating the things around you as pure substances or mixtures.
Ans-Pure substance- Sugar, Eating salt, Water, Iron, Oxygen, carbon dioxide ets
Mixture- solution of water and salt, Milk, Tea, Air, mud, etc.
Q11-Which separation technique will you apply for the separation of the following ?
(a) Sodium chloride from its solution in water.
(b)Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c)Small pieces of metal in the engine oil of a car.
(d)Different pigments from an extract of flower petals.
(e)Butter from curd .
(f)Oil from water.
(g)Tea leaves from tea.
(h)Iron pins from sand.
(i)Wheat grains from husk.
(j)Fine mud particles suspended in water.
Ans-
(a) Sodium chloride from its solution in water.
-Crystallization
(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
-Hand-picking
(d) Different pigments from an extract of flower petals.
-Chromatography
(e) Butter from curd
-Centrifugation
(f) Oil from water.
– Separating funnel
(g) Tea leaves from tea.
-Filtration
(h) Iron pins from sand.
-Magnetic separation
(i) Wheat grains from husk.
-Winnowing
(j) Fine mud particles suspended in water.
– Centrifugation
Q12-Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.
Ans-Take a few cups of water as a solvent to dissolve tea and sugar, Heat the mixture which will make the solution of all of these solutes. Filtering the tea through stainer, the soluble part of tea filtrates, and the insoluble part remains as a residue on the stainer.
Q13-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 the substance dissolved in 100 gms of water to form a saturated solution).
(a)What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 gms of water at 313 K ?
(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.
(c)Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature ?
(d)What is the effect of change of temperature on the solubility of a salt?
Ans. At 313 K 100 g of water needed to dissolve-62 g of potassium nitrate then on the same temperature 50 g of water can dissolve =(62/100) x50 =31 g of potassium nitrate.
(b)The amount of potassium chloride increases with the increase in temperature in making a saturated solution so when it is left to cool at room temperature it will precipitate at the bottom of the solution.
(c)The solubility of each salt is as follows.
Potassium nitrate –32 g
Sodium chloride-36 g
Potassium chloride-35 g
Ammonium chloride-37 g
Ammonium chloride has the highest solubility.
(d)The solubility of salt increases with the increase of temperature.
Q14-Explain the following giving examples.
(a)Saturated solution
(b)Pure substance
(c)Colloid
(d)Suspension
Ans-
Saturated solution- The solution in which further addition of solute does not dissolve is known as a saturated solution.
The pure substance-Pure substance is the substance in which all the particles are of the same kind, these are of two kinds (a) elements- hydrogen, iron, etc (b)compounds- water, carbon dioxide, etc.
Colloid-Colloids are the kind of mixture that looks like a solution but actually are heterogeneous mixture. Its particles are more than the size of the solution but far less than the size of suspension. It makes a beam of light visible when passed through it, this phenomenon is known as the Tyndall effect. As an example milk, air etc.
Suspension-Suspensions are the kind of mixture whose size of particles is more than the particle size of solution and colloid. The particle size are large enough to reflect the light so it can be seen by naked eyes. As an example: a mixture of soil and water etc.
Q15-Classify each of the following as a homogenous or heterogeneous mixture.
Soda water, wood, air ,soil, vinegar, filtered tea.
Ans-
Soda water- homogeneous
Wood- homogeneous
Air- homogeneous
Soil- heterogeneous
Vinegar- homogeneous
Filtered tea- homogeneous
Q16-How would you confirm that a colorless liquid given to you is pure water?
Ans-Pure water is not a good conductor of electricity, so we will pass electricity through it, if the current does not pass through it then it is pure water.
Q17-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-
(a) Ice is a pure substance because its each particle is the same ; that is H2O.
(b) Milk is an impure substance because it is a mixture of different substances like calcium, vitamins, proteins, and fats.
(c) Iron is an element because its all particles are the same, so it is a pure substance.
(d) Hydrochloric acid is a compound, it’s all particles are the same,so it is a pure substance.
(e) Calcium oxide is a compound, its all particles are the same , so it is a pure substance.
(f) Mercury is an element, its all particles are of the same type so it is a pure substance.
(g) Brick is a mixture of different substances that exist in the soil, so it is impure.
(h) Wood is made of single-particle “cellulose”it is made of pure substance but it is not pure substance.
(i) Air is a mixture of different gases like oxygen, nitrogen, carbon dioxide, water vapor, and other gases, so it is not a pure substance.
Q18-Identify the solution among the following mixture.
(a)Soil
(b)Seawater
(c)Air
(d)Coal
(e)Soda water
Soil- Soil is a heterogeneous mixture of inorganic and organic substances, so it is not a solution.
Sea water-Sea water is a homogeneous mixture of salts and water, so it is a solution.
Air- Air is a homogeneous mixture of oxygen, nitrogen, carbon dioxide, water vapor, and other gases, so it is a solution.
Coal- Coal is a homogeneous mixture of carbon and cellulose.
Soda water-It is a homogeneous mixture of soda and water.
Q19-Which of the following will show the “Tyndall effect”?
(a)Salt solution
(b)Milk
(c)Copper sulfate solution
(d)Starch solution
Ans- (a), (c) and (d) are solutions , particles of solutions are too small to show Tyndall effect. Milk is colloid, its particles are larger enough to show Tyndall effect.
Q20-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
(j)Blood
Ans-
Elements-Sodium, silver, tin, and silicon
Compounds-Calcium carbonate, soap, methane, and carbon dioxide
Mixture-Soil, sugar solution, coal, air, and blood.
Q21-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 the candle.
Ans-
(a)Physical change
(b)Chemical change
(c)Physical change
(d)Chemical change
(f)Physical change
(h)Candle becomes small after melting,it is a physical change. The burning of candles releases water vapor and carbon dioxide, it is a chemical change.
Brief notes on the chapter ‘ Is matter around us pure?’
Aqueous Solution: The solution of any substance in water is known as an aqueous solution.
Tyndall Effect: The scattering of the light by the particles of a colloid solution is known as Tyndall Effect.
Universal Solvent: Water is called a universal solvent because it has the ability to dissolve almost every substance.
Saturated Solution: A solution in which no more quantity of a solute can be dissolved at the given temperature is known as a saturated solution.
Mixture: A mixture is a combination of two or more substances (elements or compounds) mixed in any proportion.
Element: An element is a pure form of the substance which is made of same types of particles(i.e atoms).
Compound: A compound is a substance composed of two or more elements combined chemically in a definite proportion by mass, compound is also a pure form of a substance made of different particles(atoms).
Sublimation: The process in which any solid directly changes to a gaseous state on heating and gaseous state changes to a solid state on cooling without passing through a liquid state is known as sublimation.
Evaporation: The process of slow conversion of a liquid into vapor state at any temperature is called evaporation.
Condensation: The process of slow conversion of any gaseous substance to a liquid state on cooling is called condensation.
Sublimate: A solid residue formed from a gaseous state on the cooling of vapors of any sublimable substances.
Filtrate: The clear solution which passes out of the filter paper during the process of filtration is called filtrate.
Residue: The insoluble substance left on the filter paper during the process of filtration is known as the residue.
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