RBSE Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure?

Rajasthan Board RBSE Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure? Textbook Exercise Questions and Answers.

RBSE Class 9 Science Solutions Chapter 2 Is Matter Around Us Pure?

RBSE Class 9 Science Chapter 2 Is Matter Around Us Pure? InText Questions and Answers

Page No. 15

Question 1.
What is meant by a substance?
Answer:
A substance is a matter which has a specific composition and specific properties. Every pure element or compound is a substance.

Question 2.
List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
Homogeneous Mixture:
Mixture which has a uniform composition throughout.
Example : Sugar in water.

Heterogeneous Mixture:
Mixture which contain physically distinct parts and have non-uniform composition.
Example : Mixture of salt and sulphur.

Page No. 18

Question 1.
Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:

Homogeneous Mixture	Heterogeneous Mixture
1. Components are uniformly distributed throughout the mixture.	1. Components are not completely mixed and can be identified.
2. No visible boundaries of separation.	2. Visible boundaries of separation.
3. Same composition. Examples: Rainwater, vinegar, etc.	3. Different composition. Examples: Seawater, pizza, etc.

Question 2.
How are sol, solution and suspension different from each other?
Answer:

Question 3.
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.
Answer:
Mass of solute (NaCl) = 36 g
Mass of solvent (H₂O) = 100 g
Mass of solution (NaCl + H₂O) = 136 g

Hence, the concentration of the solution is 26.47%.

Page No. 24

Question 1.
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?
Answer:
The mixture of miscible liquids whose boiling point difference is more than 25°C such as kerosene and petrol can be separated by a technique called simple distillation. The principle of separation is based on the volatility of the substances.

Question 2.
Name the techniques used to separate the following :
(i) Butter from curd
(ii) Salt from seawater
(iii) Camphor from salt
Answer:
(i) The butter is separated from the curd by the process of centrifugation.
(ii) Simple evaporation is used to separate salt from seawater.
(iii) Camphor does not undergo liquid phase during the phase change. Therefore, sublimation process is used for the separation of camphor from salt.

Question 3.
What type of mixtures are separated by the technique of crystallisation?
Answer:
Crystallisation is a technique of separation of solid from a liquid solution. It can be used to purify solid with some impurities in it. For example – Salt from seawater.

Question 1.
Classify the following as physical or chemical changes :
Cutting of trees, melting of butter in a pan, rusting of almirah, boiling of water to form steam, passing of electric current through water and water breaking down into hydrogen and oxygen gases, dissolving common salt in water, making fruit salad with raw fruits, burning of paper and wood.
Answer:
Physical changes:

• Cutting of trees
• Melting of butter in a pan
• Boiling of water to form steam
• Dissolving common salt in water
• Making fruit salad with raw fruits

Chemical changes:

• Rusting of almirah
• Passing of electric current through water and water breaking down into hydrogen and oxygen gases
• Burning of paper and wood

Question 2.
Segregate the things around you as pure substances and mixtures.
Answer:
Pure substances : water, salt, iron, diamond
Mixture : sand, salad, concrete, air, steel

RBSE Class 9 Science Chapter 2 Is Matter Around Us Pure? Textbook Questions and Answers

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:

Substance	Separation Method
(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
(d) Different pigments from an extract of flower petals	Chromatography
(e) Butter from curd	Centrifugation
(f) Oil from water	Separating funnel
(g) Tea leaves from tea	Filtration
(h) Iron pins from sand	Magnetic separation
(i) Wheat grains from husk	Winnowing/Sedimentation
(j) Fine mud particles suspended in water	Decantation and filtration

Question 2.
Write the steps you would use for making tea. Use the words solution, solvent, dissolve, solute, soluble, insoluble, filtrate, and residue.
Answer:

• We take a cup of milk in a vessel that acts as a solvent and heat it.
• We drop the tea leaves or the powdered tea leaves into the milk as solute and continue heating.
• The tea leaves or the powdered tea leaves used are insoluble in the milk and visible even after the heating.
• Now, to the boiling solution, add sugar and stir it.
• The sugar acts yet another solute, but in this case, it is soluble in the solvent.
• Due to continued stirring, the sugar completely becomes soluble in the tea solution and a saturation level is reached.
• After enough heating, filter the solution using a medium. When done, the insoluble tea leaves stay behind as residue and the soluble essence and sugar passes through the filter medium and is collected as the filtrate.

Question 3.
Pragya tested the solubility of three different substances at different temperatures and collected the data, which is given in the following table (as grams of substance dissolved in 100 grams 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?
(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:
(a) Mass of KNO₃ required to produce a saturated solution of KNO₃ in 100 g of water at 313 K = 62 g
Mass of potassium nitrate required to produce a saturated solution in 50 g of water = 62 × (50 ÷ 100) = 31
Hence, 31 g of potassium nitrate is required.
(b) Crystals of potassium chloride will be obtained on cooling the solution.
(c) Solubility of each salt at 293 K is as follows :

• Potassium nitrate = 32 g
• Sodium chloride = 36 g
• Potassium chloride = 35 g
• Ammonium chloride = 37 g

Thus, ammonium chloride salt has the highest amount of solubility when compared to any other salt at 293 K.
(d) Solubility of a salt increases with temperature.

Question 4.
Explain the following giving examples :
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Answer:
(a) Saturated solution : A saturated solution is a solution in which the maximum amount of solute has been dissolved at a particular temperature.
For example- When sugar is dissolved repeatedly in water, a condition is reached at which further dissolution of sugar is not possible.
(b) Pure substance : Pure substance consists only one type of atoms or molecules or compounds. For example- Salt, sugar, etc.
(c) Colloid : A colloid is a heterogeneous mixture in which one substance is scattered as very fine particles in a continuous medium of another substance. These particles cannot be seen by naked eyes. For example – Ink, Blood.
(d) Suspension : A suspension is a heterogeneous mixture containing solid particles that are big enough to settle down. Particles of suspension are visible to the naked eyes. For example – Chalk powder, Paints, etc.

Question 5.
Classify each of the following as a homogeneous/heterogeneous mixture : soda water, wood, air, soil, vinegar, filtered tea.
Answer:
Homogeneous : soda water, vinegar, filtered tea.
Heterogeneous : wood, air, soil.

Question 6.
How would you confirm that colourless liquid, given to you is pure water?
Answer:
If the colourless liquid boils at 100°C, then it is pure water. This is because pure’ substance has fixed boiling and melting points.

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:
Ice, iron, hydrochloric acid, calcium oxide and mercury are the pure substances.

Question 8.
Identify the solutions among the following mixtures :
(a) Soil,
(b) Seawater,
(c) Air,
(d) Coal,
(e) Soda water.
Answer:
Seawater, air and soda water are the solutions.

Question 9.
Which of the following will show “Tyndall effect”?
(a) Salt solution,
(b) Milk,
(c) Copper sulphate solution,
(d) Starch solution.
Answer:
Milk and starch solution will show Tyndall effect.

Question 10.
Classify the following into elements,
(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	Soil
Silver	Soap Sugar	Solution
Tin	Methane	Coal
Silicon	Carbon dioxide	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 changes are chemical changes:
(a) Growth of a plant
(b) Rusting of iron
(d) Cooking of food
(e) Digestion of food
(g) Burning of a candle