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NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure?

NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure?

 

Class 9 Science NCERT Textbook Page 15

Question:- 1. What is meant by a substance?

Answer:- Pure substance refers to a material made up of only one sort of particle.

Question:- 2. List the points of differences between homogeneous and heterogeneous mixtures.

Answer:-

Heterogeneous mixture

Homogeneous mixture

All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.

Particles are uniformly distributed throughout the mixture

Irregular composition

Has a uniform composition

Noticeable boundaries of division.

No apparent boundaries of division

Example: seawater, blood, etc.

Example: rainwater, vinegar, etc.

Class 9 Science NCERT Textbook Page 18

Question:- 1. Differentiate between homogeneous and heterogeneous mixtures with examples.

Answer:-

Heterogeneous mixture

Homogeneous mixture

All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.

Particles are uniformly distributed throughout the mixture

Irregular composition

Has a uniform composition

Noticeable boundaries of division.

No apparent boundaries of division

Example: seawater, blood, etc.

Example: rainwater, vinegar, etc.

Question:- 2. How are sol, solution and suspension different from each other?

Answer:-

Sol

Solution

Suspension

It is Heterogeneous mixture.

It is Homogeneous mixture.

It is Heterogeneous mixture.

The size of the particle is 10-7 – 10-5 cm

The size of the particle is less than 1nm

The size of the particle is more than 100nm

It show tyndall effect

It doesn’t show tyndall effect

 It may or may not show tyndall effect

It usually has glassy and clear appearance

It usually has unclouded and clear appearance

It usually has cloudy and opaque appearance

It is visible with an ultramicroscope

It is not visible

It is visible with naked eye

It diffuses very slowly

It diffuses rapidly

It do not diffuse

It is pretty stable

It is highly stable

It is unstable

Get settled in centrifugation

Do not settle

Settle on their own

Eg..Milk, blood, smoke

Eg..Salt solution, Sugar solution

Eg..Sand in water, dusty air

Question:- 3. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

Answer:-  Mass of solute (NaCl) = 36 g

Mass of solvent (H2O) = 100 g

Mass of solution (NaCl + H2O) = 136 g

Concentration = Mass of solute/Mass of solution x 100

Concentration = 36/136 x 100 = 26.47%

Hence, the concentration of the solution is 26.47%

Class 9 Science NCERT Textbook Page 24

Question:- 1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25ºC), which are miscible with each other?

Answer:-

How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25 C which are miscible with each other

Question:- 2. Name the technique to separate

(i) butter from curd,

(ii) salt from sea-water,

(iii) camphor from salt.

Answer:- (i) Centrifugation,

(ii) Evaporation,

(iii) Sublimation.

Question:- 3. What type of mixtures are separated by the technique of crystallisation?

Answer:- Crystallisation is a procedure for purifying solids that include impurities. For example, salt from seawater.

Class 9 Science NCERT Textbook Page 24

Question:- 1. 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.

Answer:-

Physical change

Chemical change

Cutting the trees

Rusting of almirah

Boiling of water to form steam

Passing of electric current through water, and water breaking into hydrogen and oxygen gases

Melting of butter in a pan

Burning of paper and wood

Making a fruit salad with raw fruits

 

Dissolving common salt in water

 

Question:- 2. Try segregating the things around you as pure substances or mixtures.

Answer:- Pure substances—Water, sugar, salt, diamond and gold.

Mixtures—Steel, salad, plastic, paper, milk and air.

 

 

Exercises

Question:- 1. Which separation techniques 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.

Answer:-  

  1. Evaporation
  2. Sublimation
  3. Filtration or Centrifugation or decantation
  4. Chromatography
  5. Centrifugation
  6. separating funnel
  7. Filtration
  8. Magnetic separation
  9. Winnowing
  10. Centrifugation

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

Answer:-   1. Heat a cup of water in a container to act as a solvent.

  1. Toss in some sugar, which is soluble. Heat it until all of the sugar has dissolved.
  2. You make a water-sugar solution.
  3. Sugar is entirely soluble in water.
  4. Add half a tea-spoon of tea leaves, which are water insoluble.
  5. Bring the contents to a boil, then add the milk, which is also water soluble.
  6. Use a strainer to filter the tea; the tea in the cup is the filtrate, and the tea leaves on the strainer are the residue.

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).

Ch 2 science class 9 exercise question 2

(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?

(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?

Answer:-

Ch 2 science class 9 exercise question 2 answer

Question:- 4. Explain the following giving examples.

(a) saturated solution

(b) pure substance

(c) colloid

(d) suspension

Answer:-  (a) A saturated solution is one in which no more solute can be dissolved at a specific temperature. At room temperature, for example, no more sugar can be dissolved in an aqueous solution of sugar.

(b) A pure substance is one that is made up of only one type of particle, meaning that all of the material’s constituent particles have the same chemical properties. For instance, water, sugar, and salt.

(c) A colloid is a heterogeneous mixture containing particles that are not as small as those in a solution but are so small that they cannot be seen with the naked eye. When a light beam is passed through a colloid, the path of the light is visible. For instance, milk, smoking, and so on.

(d) A suspension is a heterogeneous mixture of solids and liquids. Suspended solute particles do not dissolve; instead, they remain suspended throughout the medium. Paints, muddy water chalk water combinations, and so on.

Question:- 5. Classify each of the following as a homogeneous or heterogeneous mixture. soda water, wood, air, soil, vinegar, filtered tea.

Answer:- Homogeneous mixtures: Soda water, air( pure), vinegar, filtered tea

Heterogeneous mixtures: Wood, soil, air ( polluted)

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

Answer:- Take a sample of colourless liquid and place it on the stove; if it begins to boil at exactly 100 degrees Celsius, it is pure water. The boiling point of any other colourless liquid, such as vinegar, is always different. Also, keep in mind that over a period of time, the entire liquid will evaporate, leaving no behind.

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.

Answer:-  (a) Ice, (c) Iron, (d) Hydrochloric acid, (e) Calcium oxide and (f) Mercury are pure substances

Question:- 8. Identify the solutions among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water.

Answer:- (b) Sea water, (c) Air and (e) Soda water are mixture.

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

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution.

Answer:- (b) Milk And (d) Starch solution.

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

Answer:- Elements:-  Sodium, Silver, Tin and Silicon.

Compounds:-  Calcium carbonate, Methane and carbon dioxide.

Mixtures:- Soil, Sugar, Coal, Air, Soap and 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.

Answer:- Among all following are chemical changes:-

(a) Growth of a plant

(b) Rusting of iron

(d) Cooking of food

(e) Digestion of food

(g) Burning of candle