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 100^oC at 1 atmospheric pressure. If the given colourless liquid boils at even slight above or below 100^oC , then the given liquid is not pure water. It must boil at sharp 100^oC.

 

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.