NCERT solutions for class 9th // Science // Chapter 2- Is matter around us pure

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NCERT solutions for class  9th // Science //  Chapter 2-  Is matter around us pure

 Chapter 2-  Is matter around us pure

                                Page No. 15 

Q1. What is mean by a substance? 
Ans- A  pure substance made up of single type of particles .

Q2. List the points of differences between homogeneous and heterogeneous mixture? 
Ans- Homogeneous mixture 
  • A mixture of uniform composition of all the substance throughout it is called homogeneous  mixture.  
  • It does not show visible boundaries of separation.
  • A mixture of sugar in water here the composition of the sugar and water is similar
  • The mixture of two visible liquid in is also homogeneous mixture 
  • example - a mixture of water and alcohol 
Heterogeneous mixture 
  • A mixture of non uniform composition of all substance throughout it is called heterogeneous  mixture .
  • It shows the visible boundaries of separation
  • The mixture of sugar and sand 
  • The mixture of immiscible liquid like oil and water.
                                  Page No. 18 

Q1. How are  Sol, solution and suspension different from each other
Ans - 

Q2. To make a saturated solution 36 gram of sodium chloride is dissolved in 100 gram of water at 293 K find its concentration at this temperature
Ans- Given, 
Mass of solute sodium chloride =  36 gram
Mass of solvent water= 100 gm
Mass of solution = mass of solute + mass of solvent
36 gm + 100gm = 136 gm
Percentage of concentration = mass of solute/ mass of solution x 100 
= 36/136  x  100 = 26.47% 

                            Page No 24 
Q1. How will you separate a mixture containing kerosene and petrol difference in their boiling point is more than 25°C which are miscible with each other? 
Ans-  the mixture of kerosene and petrol are miscible liquid so it can be e separated by the method of distillation.
  • Take a mixture in a distillation flask
  •  Fit with a fitted with a thermometer to  count temperature 
  • Arrange the apparatus as shown in figure 
  • Then heat the mixture slowly
  •  Petrol is evaporates first because it has low boiling point than the kerosene 
  •  It condenced in the condenser and collect in another container 
  •  Kerosene is left  in the distillation flask



Q2. Name the technique of separate 
a) Butter from curd
b)  Salt from seawater 
c) Camphor from Salt 
Ans- a) Centrifugation   b) Evaporation  c)  Sublimation. 

Q3. What type of mixtures are separated by the technique of crystallization? 
Ans- Crystallization method is used to separate a pure solid in the form of its crystal from a impure solution of it .

Q4. Classify the following as chemical or physical changes
  1. Cutting of trees 
  2. Melting of butter in a pan 
  3. Rusting of almirah
  4. Boiling of water to form steam
  5. Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
  6. Dissolving common salt in water
  7. Making a fruit salad with raw fruit
  8. Burning of paper and wood
Ans 
  1. Physical change
  2. Physical change
  3. Chemical change
  4. Physical change
  5. Chemical change
  6. Physical change
  7. Physical change.
  8. Chemical change
Q5. Try segregating the things around you as pure substance or mixture
Ans - Pure substances -  Gold , iron , bread ,sugar, water ,wheat
Mixture - Plastic,  paper, milk , Steel ,stainless steel ,bronze

                        Exercise
 Q1. Which separation technique 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.
Ans  - a) Evaporation 
b) Sublimation
c) Filtration 
d) Chromatography
e) Centrifugation 
f) Separating funnel
g) Filtration
h) Magnetic separation
i) Winnowing/  Sedimentation
j) Decantation and Filtration

Q2. Write the steps you would use for making tea use the words solution solvent solute dissolved soluble insoluble filtrate and residue.
Ans - 
  • Take a cup of water in a container as a solvent and heat it.
  • Add some sugar in it which is solute and again heat it up to sugar dissolve in it because it is soluble in water
  • Add some tea spoon of tea leaves in that water these are insoluble in water 
  • Add some milk in it which is also soluble in water.
  • Boil all the mixture for sometime.
  • Then you get the solution  filter the tea leaves with the help of strainer the tea collected in Cup is a filtrate while the tea leaves collected on strainer 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 gram of water to form a saturated solution. 


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 - mass of kno3 to produce a saturated solution of kno3 in 100 gm of water at 313 k= 62 gm .
:. Mass of KNO3 in 50 gm of water at 313K 
          = 62.0 x 50 / 100 = 31.0 gm 
b) Pragya makes a saturated solution of potassium chloride in water at 353 Kelvin and leaves a solution to cool at room temperature what would she observed as the solution cools?  explain. 
Ans - Crystals 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
Ans 
  • solubility of each salt at 293 K is
  • Potassium nitrate 32 gram
  • Sodium chloride 36 gram
  • Potassium chloride 35 gram
  • Ammonium chloride 37 gram

d) What is the effect of change of temperature on the celebrity of a salt . 
Ans - On increasing the temperature the solubility of a salt increases

Q4. Explain the following giving examples.
a) saturated solution
b) pure substance
c) colloid 
d) suspension.

Ans- a) saturated solution - In a fixed amount of solvent when no more solute can be dissolved for the at a given temperature is called saturated solution.
b) pure substance -A  pure substances is made up of  single type of the particles eg - gold , silver, copper. 
c) colloid - In a colloid solution the size of the solute particle is bigger than the true solution and these particles are cannot be seen by naked eyes they are stable in nature eg - blood , ink 
d) Suspension  - Suspension is a heterogeneous mixture in which the solute particles are big in size and so that they settle down at bottom.
eg. - chalk water , paints etc. 


Q5 . Classify each of the following as a homogeneous  and heterogeneous mixture soda water would air oil vinegar filtered tea
Ans- 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? 
Ans- The pure substance have a fixed melting and boiling point if the colourless liquid boil at 100°C  then it is clear that its pure water.

Q7 . Which of the following materials fall in the category of pure substance
Ice ,milk, iron, hydrochloric acid, calcium oxide, mercury, brick, wood, air.
Ans -Pure substance - Ice , iron, mercury ,Hydrochloric acid , Calcium oxide

Q8. Identify the solutions among the following mixture
Soil, sea water ,coal ,soda water.,air
Ans -  sea water , soda water , air
 
Q9 . Which of the following will show tyndall effect
Salt solution ,milk,copper sulphate solution ,starch solution.
Ans -  Milk , starch solution 

Q10. Classify the following into elements compounds and mixtures.
Sodium, soil ,sugar solution ,silver, calcium carbonate ,tin, silicon ,coal, air, soap, methane, carbon dioxide ,blood.
Ans- Compounds - Calcium carbonate , carbon dioxide. Soap
Mixture - Soil, sugar solution, coal, air ,blood
Elements -  Sodium , silver, tin , silicon , methane 

Q11. Which of the following are chemical changes.
  1. Growth of a plant 
  2. Rusting of iron 
  3. Mixing of iron fillings and sand
  4.  Cooking of food 
  5. Digestion of food 
  6. Freezing of food
  7.  Freezing of water 
  8. Burning of a candle
Ans - 
Chemical change - Growth of plant,  Rusting of iron ,cooking of food ,digestion of food ,burning of candle

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