Science class 9– Chapter 2 – Is Matter around us Pure?– NCERT Exercise Solution ( Question-Answer) –

Science Class 9 -Chapter 2 – Is Matter around us Pure? – NCERT Exercise Solution (Question-Answer) is provided below. Total 11 Questions are in this NCERT Exercise, all are solved here.

Q1. Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.

Answer: Sodium chloride from its solution in water is separated by the technique of Evaporation.

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

Answer: Ammonium chloride from a mixture containing sodium chloride and ammonium chloride is separated by the technique of Sublimation.

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

Answer: Small piece of metal in the engine oil of a car is separated by the technique of Filtration.

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

Answer: Different pigments from an extract of flower petals are separated by the technique of Chromatography.

(e) Butter from curd.

Answer: Butter from curd is separated by the technique of Centrifugation.

(f) Oil from water.

Answer: Oil from water is separated by the technique of Separating Funnel.

(g) Tea leaves from tea.

Answer: Tea leaves from tea is separated by the technique of Filtration

(h) Iron pins from sand.

Answer: Iron pins from sand is separated by the technique of Magnetic Separation.

(i) Wheat grains from husk.

Answer: Wheat grains from the husk is separated by the technique of Winnowing / Sedimentation.

(j) Fine mud particles suspended in water.

Answer: Fine mud particles suspended in water is separated by the technique of Decantation and Filtration.

Q2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Answer: 👉Steps we would use for making tea:-

(i) We take a cup of water in a container which is solvent, supply it with heat.

(ii) Add sugar (solute) in water and heat it till all sugar dissolves.

(iii) We get a solution of water and sugar because sugar is a type of solute which completely dissolve in water (solvent)

(iv) Now add a half teaspoon of tea-leaves, tea leaves are insoluble in water.

(v) Add milk which is also soluble in water, and boil the content.

(vi) At last filter the tea with the help of a strainer, we observe that tea collected in the cup is filtrate and the tea-leaves collect on the strainer which is residue.

Q3.  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                         The temperature in K
283           293              313               333                 353                                   Solubility            
Potassium nitrate21               32                 62                106               167
Sodium chloride36               36                  36                 37               37
Potassium chloride35               35                 40                  46               54
Ammonium chloride25               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?

Answer: Given: Mass of potassium nitrate required to produce a saturated solution in 100 g of water at 313 K = 62 g

  To find: Mass of potassium nitrate required to produce a saturated solution in 50 g of water at 313 K = 620 * 50 / 100 = 31.0 g

Hence, 31 g potassium nitrate  is required .

(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.

Answer: The solubility of potassium chloride in water is decreased when a saturated solution of potassium chloride loses heat at 353K. So, the crystal of potassium chloride will be obtained on cooling the saturated solution.

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

Answer: Solubility of each salt at 293 K is

  • Potassium nitrate = 32 g
  • Sodium chloride = 36 g
  • Potassium chloride = 35 g
  • Ammonium chloride = 37 g

We observe that ammonium chloride salt has the highest amount of solubility when compared to any other salt at 293 K.

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

Answer: When the temperature increase, the solubility of salt also increases. The given table also clearly depict that solubility of salt-dependent upon temperature and increase with the increase in temperature.

So, when a salt at a specific temperature arrives at its saturation point, there is a propensity to dissolve more salt through an increase in the temperature of the solution.

Q4. Explain the following giving examples.

(a) Saturated solution

Answer: Saturated solution is a chemical solution in which at a specific temperature when no more soluble without an increase in the temperature. 

Example: If we add enough sugar into water, we can form a saturated solution. we will know we have reached at the saturation level when the sugar stops dissolving. Hot water allows much more sugar to be dissolve than cold.

(b) Pure substance

Answer: A substance that is made up of only one kind of particle is known as a pure substance. It cannot be separated into constituents by the physical or chemical process.

(c) Colloid

Answer: A solution in which the size of solute particles is bigger than that of the true solution is known as a colloid.

Example: milk, blood etc.

It is comprised of ultramicroscopic particles substance that would be scattered through another substance. These particles cannot be seen with our naked eyes, they are stable.

(d) Suspension

Answer: A heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it is known as suspension. These particles can be seen by the naked eye.

Example: chalk – water mixture etc.

Q5. Classify each of the following as a homogeneous or heterogeneous mixture.

 Soda water, wood, air, vinegar, filtered tea.

Answer: 👉Homogeneous Mixture: Soda water, vinegar, filtered tea.

👉 Heterogeneous Mixture: Wood, air, soil.

Q6. How would you confirm that a colourless liquid given to you is pure water?

Answer: We know that pure substances have a fixed melting or boiling point. We confirm that a colourless liquid given to us is pure water by finding the boiling point of the given colourless liquid. It is said to be pure water if it boils at 100 degrees C. But if there is a decrease or increase in the boiling point, we infer that water has added impurities hence not pure.

Q7. 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.

Answer: 👉Following materials falls in the category of “pure substance”

 (a) Ice

(c) Iron

(d) Hydrochloric acid

(e) Calcium oxide

(f) Mercury

Q8. Identify the solution among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water

Answer: Following are the solution which is given above in question:-

(b) Sea water

(c) Air

(e) Soda water

Q9. Which of the following will show the “Tyndall effect”?

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution

Answer: Following will show the Tyndall effect:

           (b) Milk

           (d) Starch solution

Q10. 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

Answer: 👉Elements: silicon, silver, sodium, tin.

     👉Compounds: carbon dioxide, methane, calcium carbonate.

     👉Mixture: sugar solution, air, coal, blood, soap, soil.

Q11. Which of the following are chemical changes?

(a) Growth of 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.

Answer: 👉 Following are the chemical changes-

(a) Growth of plant

(b) Rusting of iron

(d) Cooking of food

(e) Digestion of food

(g) Burning of a candle

Science Class 9– Chapter 2 – Is Matter around us Pure?- NCERT Exercise solution (Question-Answer) ended👍👍👍

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