SCIENCE || CLASS 9TH || CHAPTER 02 || INTEXT QUESTIONS AND ANSWERS || CBSE AND MP BOARD

AKC CHATURVEDI August 12, 2021

  ''AKC SCIENCE CLASSES"

CLASS 09 TH (CBSE AND MP BOARD)


"CHAPTER 02"


"IS MATTERS AROUND US PURE"


"INTEXT QUESTIONS"


NCERT INTEXT QUESTIONS (PAGE NO:- 15)


Question 01:- What is meant by a pure substance?

Ans:- Substance having single type of particles is known as pure substance.

For example :- Hydrogen, Water etc., are pure. 

Note:- All elements and compounds are considered to be pure. 

Question 02:- List the points of differences between homogeneous and heterogeneous mixtures. 

Ans:- 

(a). Homogeneous mixture

  • Its constituent’s particles cannot be seen easily.
  • There are no visible boundaries of separation in a homogeneous mixture.
  • Its constituents cannot be easily separated.

Examples :- Alloys, solution of salt in water etc.

(b) Heterogeneous mixture

  • Its constituent particles can be seen easily.
  • Have visible boundaries of separation between the constituents. 
  • Its constituents can be separated by simple methods.

Examples :- Mixture of sand and common salt, mixture of sand and water etc.

NCERT INTEXT QUESTIONS (PAGE NO:- 18)

Question 01:- Differentiate between homogeneous and heterogeneous mixture with example.

Ans:- (a). Homogeneous mixture

  • Its constituent’s particles cannot be seen easily.
  • There are no visible boundaries of separation in a homogeneous mixture.
  • Its constituents cannot be easily separated.

Examples :- Alloys, solution of salt in water etc.

(b) Heterogeneous mixture

  • Its constituent particles can be seen easily.
  • Have visible boundaries of separation between the constituents. 
  • Its constituents can be separated by simple methods.

Examples :- Mixture of sand and common salt, mixture of sand and water etc.

Questions 02:- How are sol, solution and suspension different from each other?

Ans:-

(a) Solution :-

  • Solution or true solution is homogeneous.
  • NO Tyndall effect.
  • Solute particles cannot be filtered by using a filter paper.
  • True solution is transparent.

Examples :- Sea water, alloys, solution of lemon juice in water etc.

(b) Sol (colloidal solution) :-

  • Sol or colloidal solution is heterogeneous.
  • Tyndall effect.
  • Cannot be separated by ordinary filter paper.
  • It may be transparent or translucent.

Examples :- Milk of magnesia, cough syrup, mist, fog, clouds, smoke, mud etc. 

(c) Suspension :-

  • Suspension is also heterogeneous.
  • Tyndall effect.
  • It may be transparent or translucent.
  • Separated easily by filter paper.(because of large particles)

Examples :- Mixture of sand in water, mixture of chalk in water.

Question 03:- 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.

Ans:-

Mass of sodium chloride (solute) = 36 g

Mass of water (solvent) = 100 g

We know that, mass of solution = mass of solute + mass of solvent

           = 36 g+ 100 g = 136 g

Concentration (mass percentage) of the solution

       Mass of Solute

= ---------------------- x 100 

     Mass of Solution

      36g 

= --------- x 100 = 26.47%

    136 g

NCERT INTEXT QUESTIONS (PAGE NO:- 24)

Question 01:- 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?

Solution:- Simple distillation is the method which can separate the 

mixture of kerosene and petrol (b.p. differ by more than 25°C).

Method :- In a distillation flask, a mixture of kerosene and petrol is taken as shown in figure. The mixture is heated slowly and the temperature is recorded with the help of thermometer. Petrol (b.p. = 70° C to 1200 ° C) vaporizes first and the temperature becomes constant for some time (till all petrol evaporates from the mixture). Vapours of petrol are condensed and collected in another container while the kerosene remains in the distillation flask. As soon as the temperature starts’ rising again, the heating is stopped and both the components are collected separately.

Question 02:- Name the technique to separate

(i) Butter from curd

(ii) Salt from sea water

(iii) Camphor from salt

Ans:- (i) By using centrifugation method, butter can be separated from curd.

(ii) By using evaporation method, salt from sea water can be separated. Water vaporizes on evaporation leaving behind the salt.

(iii) Camphor from salt can be separated by sublimation method. On subliming camphor will be converted into vapour leaving behind the salt.

Question 03:- What types of mixtures are separated by the technique of

crystallization?

Ans:- 

Crystallization method can be used for the purification of those mixtures which 
  • Contain insoluble and/or soluble impurities.
  • Have crystalline nature.
  • Cannot be separated by filtration as some impurities are soluble. 

Question 04:- Classify the following as chemical or physical changes

(a) Cutting of trees, 

(b) Melting of butter in a pan, 

(c) Rusting of almirah,

(d) Boiling of water to form steam, 

(e) Passing of electric current, through water and the water breaking 

down into hydrogen and oxygen gases, 

(f) Dissolving common salt in water, 

(g) Making a fruit salad with raw fruits, and 

(h) Burning of paper and wood

Ans :-

Physical Change :-

Cutting of trees, 

Melting of butter in a pan,

Boiling of water to form steam,

Dissolving common salt in water,

Making a fruit salad with raw fruits.

Chemical Change :-

Rusting of almirah,

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

Burning of paper and wood.

Question 05:- Try segregating the things around you as pure substances or mixtures.

(a) Wood

(b) Coal

(c) Milk

(d) Sugar

(e) Common salt

(f) Soap

(g) Soil

(h) Rubber

Ans:-

(a) Mixture

(b) Mixture

(c) Mixture

(d) Pure substance

(e) Pure substance

(f) Compound/mixture

(g) Mixture

(h) Pure substance

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