Chapter 2

Is Matter Around Us Pure

Intext Question

Page No 15

1. What is meant by a substance?
Ans:  A pure substance is made up of only one kind of particle that is atom or molecules in substance all the particles or the same in their chemical nature.

2. List the points of difference between homogeneous and heterogeneous mixtures.

Ans: Homogeneous mixtures:

  • They have uniform composition throughout. 
  • They have physically distant pasts.  
  • They have some properties throughout the bulk. 
  • The components of the homogeneous mixture are not visible to the naked eye or even under a microscope. 

  Heterogeneous mixtures:

  • They do not have uniform composition throughout. 
  • They have physically distant parts. They have visible boundaries of separation between the various parts. 
  • They do not have the same properties throughout the bulk. 
  • The components of a heterogeneous mixture are either visible to the naked eye or under a microscope. 
Page no 18

1. Difference between homogeneous and heterogeneous mixture with examples.
Ans: For difference refer to the previous answer
Example of homogeneous mixtures: sodium chloride dissolved in water sugar dissolved in water.
Example for heterogeneous mixtures: gunpowder, mixture of chalk in water, smoke.

2. How are sol, solution, and suspension different from each other?
Characteristics Sol Solution Suspension
Mixture Type Heterogeneous Homogeneous Heterogeneous
Particle size 10-7 – 10-5cm Less than 1nm More than 100nm
Tyndall effect Exhibits the Tyndall effect   Does not exhibit the Tyndall effect May or may not be exhibited. Depends on the type of mixture
Appearance Usually glassy and clear Unclouded and clear Cloudy and opaque
Visibility Visible with an ultramicroscope Not visible Visible with the naked eye
Diffusion Very slow diffusion Rapid diffusion No diffusion takes place
Stability Quiet stable Highly stable Unstable
Settling down of the particles Get settled on centrifugation the mixture Does not settle Settle on their own        
Example Milk, blood, smoke Salt solution, Sugar solution Sand in water, dusty air
4. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 grams of water at 2:93 Kelvin. Find the concentration at this temperature.
Ans: Concentration is the amount of salt dissolved in 100 grams of solvent. So, 36 g of sodium chloride is dissolved in a hundred grams of water. Therefore, the concentration of the solution is 36 g per 100 gram of water or 36% by mass 293 Kelvin.

Page no 24

1. How will you separate a mixture containing kerosene and (difference in their boiling point is more than 25° Celsius), which are miscible with each other?
Ans: Since the mixture contains two liquids which are miscible with each other and have a boiling point difference of more than 25° celsius, these can be separated by simple distillation method.

2. Name the technologies to separate
(i)butter from curd
(ii) salt from seawater
(iii) camphor from salt
Ans: (i) centrifugation
(ii) evaporation
(iii) sublimation

3. What type of mixtures are separated by the technology of crystallization?
Ans: Crystallization technology is used to separate a mixture of those two components, in which one dissolves in a given solvent but the other remains insoluble or it is used to separate solids, in which the impurities are either insoluble or are more soluble than the solid in a particular solvent.    For example, impure copper sulphate, sea salt, etc.
Page no 24

1. Classify the following as chemical or physical changes
i. Cutting of trees,
ii. Melting of butter in a pan,
iii. Rusting of Almira,
iv. Boiling of water to form steam,
v. Passing of electrical current, through water and the water breaking down into hydrogen and oxygen gases,
vi. Dissolving common salt in water,
vii. Making a fruit salad with rough Road, and
viii. Burning of Paper and Wood.
i. Physical change
ii. Physical change
iii. Chemical change
iv. Physical change
v. Chemical change
vi. Physical change
vii. Physical change
viii. Chemical change.
2. Try segregating the things around you as pure substance or mixture.
Ans:  Pure substance: distilled water, diamond, graphite, sugar.
Mixture: curd, ice cream, kerosene oil, cooking oil, steel, alcohol, carbon dioxide, ink, air.

Exercise question with Answer

1)  Which separation techniques will you apply for the separation of the following?

  1. Sodium chloride from the solution in water.
  2. Aluminum chloride from a mixture containing sodium chloride and I am chloride.
  3. Small pieces of metal in the engine oil of a car.
  4. Different pigments from an extract of flower petals.
  5. Butter from curd.
  6. Oil from water.
  7. Tea leaves from Tea.
  8. Iron pins from sand.
  9. Wheat grains from husk.
  10. Fine mud particles suspended in water.


  1. Evaporation
  2. Sublimation
  3. Filtration
  4. Chromatography
  5. Centrifugation
  6. Separating funnel
  7. Filtration
  8. Magnetic separation
  9. Sieving or Blowing air
  10. Using alum or Filtration
2. Write the steps you would use for making tea. Use the word solution, solvent, solute, dissolves, soluble, insoluble, filter, and residue.
Ans: Take 100 ML of water which acts as a solvent. Boil water on a gas stove. Add 1 teaspoon of sugar which acts as solute. Sugar gets dissolved in water and forms a solution. Now add about half a teaspoon of tea leaves which are insoluble in water. Boil the contents for 4 to 5 minutes and add half a cup of milk and allow it to boil again for 2 to 3 minutes. Filter dirty with the help of SIEVE. The tea leaves big and insoluble remains as a residue on the SIEVE while a hot solution of tea is obtained as a Filtrate.

3. Explain the following giving examples
(a)  Saturated solution
(b)  Pure substance
(c)  Collide
(d)  Suspension
Ans: (a)Saturated solution– At any particular time, a solution that has dissolved as much salute as it capable dissolving is said to be a saturated solution.
Example:  21 g of potassium nitrate completely dissolved in hundred gram of water.
(b)Pure substance – A substance that consists of a single type of particles.
Example: oxygen
(c)Collide solution is a solution in which a material is evenly suspended in a liquid.
Example: milk
(d)Suspension– As the suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of medium.
Example:  sawdust added to water
4. Classify each of the following as a homogeneous or heterogeneous mixture
Soda water, wood, air, soil, vinegar, filtrate tea.
Ans: Homogeneous mixture: soda water, wood, air, vinegar, filtered tea.
Heterogeneous: mixture soil.

5. How would you confirm that a colourless liquid given to you is pure water?
Ans: It does not undergo Tyndall effort then the water is pure.
6. Which of the following material fall in the category of pure substances.
  • Ice
  • Hydrochloric acid
  • Break
  • Milk
  • Calcium oxide
  • Iron
  • Mercury
  • Air
Ans: Pure substance ice, iron, hydrochloric acid, calcium oxide, mercury.

7. Identify the solutions among the following mixtures.

  • Soil
  • Seawater
  • Air
  • Coll
  • Sodium water

Ans: Solution air, soda water, sea water

8. Which of the following will show the Tyndall effect?

  • Salt solution
  • Milk
  • Copper sulphate solution
  • Starch solution

Ans: Milk on the starch solution will show the Tyndall effect.

9. Classify the following into elements compounds and mixtures.
  • Sodium
  • Soil
  • Sugar solution
  • Silver
  • Calcium carbonate
  • Tin
  • Silicon
  • Air
  • Soap
  • Methane
  • Carbon dioxide
  • Blood
Ans: Elements -sodium, silver, 10, silicon, coal
Compounds- calcium carbonate, soap, methane, carbon dioxide
Mixture -Soil, sugar solution, air, blood

10. Which of the following are chemical changes?

  • Growth of plant
  • Cooking of food
  • Rusting of iron
  • Digestion of food
  • Mixing of iron filings and sand
  • Freezing of water
  • Burning of a candle

Ans: Chemical changes are rusting of iron, cooking of food, digestion of food, burning of candle.

Extra question answers

1. Give the properties of a solution
Ans: A solution is a homogeneous mixture.
The particles of a solution are smaller than 1mm in diameter.
Because of very small particle size, they do not scatter a beam of light passing through the solution, so the path of light is not visible in the solution.
The salute particles cannot be separated by filtration. The solid particles do not settle down when left undistributed.

2. What are saturated and unsaturated solutions?
Ans: At any particular temperature, a solution that has dissolved as much salute as it is capable of dissolving is said to be a saturated solution.
If the amount of solid content in a solution is less than the saturation level, it is called an unsaturated solution.

3. What are the properties of suspension?
Ans: Suspension is a heterogeneous mixture.
The particles of suspension can be seen by naked eyes.
The particles of suspension scatter a beam of light passing through it and make it Park visible.
The solid particles settle down when a suspension is left undistributed.

4. Give reason-
(a) Effect can be observed when a fine beam of light enters a room through a small hole.
(b) If I can be observed when sunlight passes through the canopy of a dense forest.
Ans: (a) This happens due to the scattering of light by the particles of dust and smoke in the air.
(b)In the forest contains droplets of water, which acts as particles of collide disappeared in the air which scatters the light.
5. Give the properties of a collide
  • A collide is a heterogeneous mixture.
  • The size of the particles of a collide is too small to be individually seen by naked eyes.
  • Colors are big enough to scatter a beam of light passing through it and make it’s part visible.
  • They do not settle down when left undistributed.
6. What is the principle behind centrifugation? Give any two applications Ans: The principle is the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. Application –
  • Used in homes do separate butter from cream.
  • Use in domestic laboratories for blood and urine tests.
7. What is chromatography? Mention its applications?
Ans: Chromatography is the technique used for separation of those solute and dissolved in the same solvent.
Used to separate colors in a dye next line to separate pigment from natural colors

8. Define(a) crystallization
Ans: (a)crystallization is a process that separates a few solid in the form of its crystals from a solution.
(b) A compound is a substance composed of two or more elements chemically combined.

9. Give the properties of metals
  • They have Lester 
  • They have silvery gray or golden yellow colour
  • They conduct heat and electricity
  • They are ductile
  • They are malleable
  • They are sonorous

Important points

  • A mixture is a substance formed by mixing two or more pure substances in any proportion so that components do not lose their identity. 
  • Types of mixtures heterogeneous mixtures and homogeneous mixtures. 
  • A mixture is said to be homogeneous if its composition is uniform throughout. 
  • A mixture in which different constraints do not mix uniformly is called a heterogeneous mixture. 
  • A solution is a homogeneous mixture of two or more substances.  
  • The component of a solution that dissolves the other component in it is called solvent. 
  • The component of a solution that is dissolved in the solvent is called solute. 
  • Depending upon the amount of solid present in a solution, it can be called a dilute, concentrated or a saturated solution. 
  • At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving is said to be a saturated solution. 
  • The amount of solute present in the saturated solution at a given temperature is called solubility.
  • If the amount of solute content in a solution is less than the saturation level, it is called unsaturated solution. 
  • The concentration of a solution is the amount of solute present in a given amount of solution, or the amount of solute dissolved in a given mass or volume of solvent. 
  • Mass by Mass percentage of solution = Mass of solute/mass of solution X100 
  • Mass by volume percentage of a solution= mass of solute/Volume of solution X100 
  • A suspension is a heterogeneous mixture in which the solute particles do not dissolve by three men suspended throughout the bulk of the medium. 
  • A Collider solution is a solution in which a material is evenly suspended in a liquid. 
  • The component of the Collider solution or the dispersion phase and the dispersion medium. 
  • Colloids are classified according to the state of the dispersing medium and the dispersed phase.
  • The scattering of a beam of light by collides is called the Tyndall effect.