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NCERT SOLUTION

CLASS 9

CHAPTER 2

IS MATTER AROUND US PURE

PAGE NO. 28 ,29 and 30

                                            EXERCISES

QUESTION NO. 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 tea.
(i) Wheat grains from sand.
(j) Fine mud particles suspended in water.

ANSWER NO. 1

(a) Evaporation.
(b) Sublimation.
(c) By using a suitable filter.
(d) Chromatography.
(e) By centrifugal machine or churning the curd by hand.
(f) Decantation.
(g) Filtration.
(h) By the process of magnetic separation.
(i) By winnowing. 
(j) Coagulation and decantation.
          Alum is added to muddy water which makes the soil particles heavier and settle down in bottom. The clean water is then separated by decantation.

QUESTION NO. 2

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

ANSWER NO. 2

For making tea following steps are to be taken -
(i)  Take 100ml of water as a solvent and boil it for few minute.
(ii)  Add one tea spoon sugar, one tea spoon tea leaves and 50ml of milk as a                  solute. 
(iii)  Boil it for few minutes so that sugar  will dissolve in solution as sugar is                  soluble in water.
(iv)  Filter the solution in a cup. The insoluble tea leaves will be left behind as               residue.

QUESTION NO. 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). 

     Substance                                   Temperature in K
     Dissolved                               283  293  313  333  353
                                                                 Solubility
Potassium nitrate                     21     32    62   106  167
Sodium chloride                       36      36    36    37    37
Potassium chloride                  35      35    40     46   54
Ammonium chloride               24      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?
(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 NO. 3

(a) The solubility of potassium nitrate at 313 K is 62gm. Hence 62gm of potassium nitrate is required to make a saturated solution of potassium nitrate in 100gm of water at 313 K.
           So to make a saturated solution in 50gms of water the required potassium nitrate will be 62/2 = 31gm.

 (b) When a saturated solution of potassium chloride at 353 K is left to cool, then the solid potassium chloride will gradually separate from the solution ( because the solubility decrease on cooling.)

 (c)  The solubility of different salts at 293 K is potassium nitrate 32gm, Sodium chloride 36gm, Potassium chloride 35gm and Ammonium chloride 37gm.
     Ammonium chloride has the highest solubility ( 37gm) at this temperature of 293 K.

 (d) According to the given data solubility of a salt increases on increasing the temperature.

QUESTION NO. 4

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

ANSWER NO. 4

(a) Saturated Solution :  At a particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be saturated solution. It is also defined as if no more solute can be dissolved in a solution at a given temperature, it is called saturated solution.

 (b) Pure Substance :  A pure substance consist of a particles which have same chemical nature. A pure substance consist of a single  type of particles.

 (c) Colloid :  In colloid particles are uniformly spread throughout the solution. Because of smaller size of particles, the  appears to be homogeneous. But colloidal solution is a heterogeneous mixture. Example : milk, blood.

 (d) Suspension :  A suspension is a heterogeneous mixture in which the solute prticles do not dissolve but remained suspended throughout the bulk of the medium. The particles of suspension are visible to the naked eyes.

QUESTION NO. 5

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

ANSWER NO. 5


     HOMOGENEOUS                            HETEROGENEOUS
         MIXTURE                                            MIXTURE
    1.  Soda Water                                 1.  Wood
    2.  Vinegar                                        2.  Air
    3. Filtered Tea                                 3.  Soil

QUESTION NO. 6

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

ANSWER NO. 6

By checking the boiling temperature of the liquid it can confirmed that given water is pure or not. If it boils at 100 C it is said be pure. But if there is a decrease or increase in the boiling point, it confirms that water has added impurities.

QUESTION NO. 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 NO. 7

PURE SUBSTANCES

  • Iron
  • Ice
  • Mercury
  • Hydrochloric Acid
  • Calcium Oxide

QUESTION NO. 8

Identify the solutions among the following mixtures.
(a)Soil
(b)Sea water
(c)Air
(d)Coal
(e)Soda water.

ANSWER NO. 8

SOLUTIONS


  • Sea Water
  • Air
  • Soda Water

QUESTION NO. 9

Which of the following will show “Tyndall effect”?
(a)Salt solution
(b)Milk
(c)Copper sulphate solution
(d)Starch solution.

ANSWER NO. 9

Milk and starch solution from the above list of solution will show ˋˋ  Tyndall effect ˋˋ .

QUESTION NO. 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 NO. 10


 COMPOUND                                   MIXTURE 
  1. Calcium Carbonate               1. Soil
  2. Carbon dioxide                      2. Sugar Solution
  3. Methane                                   3. Coal
                                                          4. Air
                                                          5. Blood
                                                          6. Soap

QUESTION NO. 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 NO. 11

CHEMICAL CHANGES

  1. Growth of plants
  2. Rusting of iron
  3. Cooking of food
  4. Digestion of food
  5. Burning of a candle

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