Class 9 - Chemistry - Is Matter Around Us Pure

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:

The separation techniques used to separate are following:-

(a) Sodium chloride from its solution in water: - Evaporation

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride: - Sublimation.

(c) Small pieces of metal in the engine oil of a car: - Filtration or Centrifugation or decantation.

(d) Different pigments from an extract of flower petals: - Chromatography.

(e) Butter from curd: - Centrifugation.

(f) Oil from water: - Using separating funnel.

(g) Tea leaves from tea: - Filtration.

(h) Iron pins from sand: - Magnetic separation.

(i) Wheat grains from husk: - Winnowing.

(j) Fine mud particles suspended in water:- 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:

  • Water is the solvent boil it in a kettle.
  • When water is boiling add sugar, tea leaves as solute.
  • Now add milk, together sugar, tea leaves and milk form solution.
  • Sugar dissolves in water.
  • Now strain the solution.
  • The tea leaves being insoluble will remain as residue.
  • Colour of tea leaves will go into the solution as filtrate.
  • The resulting solution is the required tea.

 

 

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).

Class_9_Is_Matter_Around_Us_Pure_1

  • What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in
  • 50 grams of water at 313 K?
  • 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.
  • Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
  • What is the effect of change of temperature on the solubility of a salt?

Answer:

  • Mass of KNO3 to produce a saturated solution KNO3 in 100g of water at 313 K = 62g

Therefore, Mass of KNO3 in 50gms at 313K = (62.0 x 50)/100 = 31.0g

  • The amount of potassium chloride that should be dissolved in water to make saturated solution increases with temperature.
  • Thus when the solution cools some of potassium chloride will precipitate out of the solution.
  • The solubility of the salts at 293K are:-

Potassium nitrate = 32g

Sodium Chloride = 36g

Potassium Chloride = 35g

Ammonium Chloride = 37g

Ammonium chloride has the highest solubility at 293K.

  • The solubility of salt increases with temperature.

Question 4:

Explain the following giving examples.

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

Answer:

  • Saturated Solution: - When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.
  • For example: - In the aqueous solution of sugar when no more of sugar can be dissolved at room temperature.
  • Pure substance: - A pure substance consists of a single type of particles.
  • This means all the constituent particles of that substance are the same in their chemical nature.
  • For example:-Sulphur is made up of only one kind of sulphur.
  • Colloid: - A colloid is a solution in which the size of solute particles is bigger than that of true solution.
  • These particles cannot be seen with our naked eyes, they are stable, e.g., ink, blood.
  • Suspension: - A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
  • Particles of a suspension are visible to the naked eye. For example: - paints, muddy water chalk water mixtures etc.

 

 

Question 5:

Classify each of the following as a homogeneous or heterogeneous mixture.

Soda water, wood, air, soil, vinegar, filtered tea

Answer:

          Homogeneous

         Heterogeneous

1.     Soda Water

1.Wood

2.     Air

           2.Soil

3.     Vinegar

 

4.     Filtered Tea

 

Pure Air is homogeneous mixture whereas polluted air is heterogeneous mixture.

 

 

Question 6:

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

Answer:

Every liquid has characteristic boiling point at 1 atmospheric pressure. Pure water has a boiling point of 373K at 1 atm.

Therefore we can find the boiling point of a given colourless liquid.

If the colourless liquid boils exactly at 373K at 1 atmospheric pressure then it is pure water.

If there is difference in boiling point then water is contaminated.

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:

The following materials fall in the category of a “pure substance”:-

  1. Ice
  2. Iron
  3. Hydrochloric acid
  4. Calcium oxide
  5. Mercury

Question 8:

Identify the solutions among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water.

Answer:

The following mixtures are solutions:-

  1. Sea water
  2. Air
  3. Soda water

                   

Question 9:

Which of the following will show “Tyndall effect”?

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution.

Answer:

Tyndall effect is shown by colloidal solutions.

The following will show “Tyndall effect”

  1. Milk
  2. Starch

 

 

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

  Compounds

 Mixtures

Sodium

Calcium Carbonate

Sugar solution

Silver

 Methane

 Soil

Tin

Carbon dioxide

 Coal

Silicon

Soap

 Air

 

 

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:

The following are the chemical changes:-

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

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