Class 9 Science Chapter 2 Are the Substances Around Us Pure
If you are a Class IX student searching for high-quality SEBA Class 9 Science Chapter 2 Are the Substances Around Us Pure notes to improve your exam performance, then this Ready Guide is for you. It includes all the important question-answers prepared by a team of experts. Our language is very easy to understand and remember. Begin your study journey with us for a bright future.
Are the Substances Around Us Pure
Answers to Questions Within the Lesson(1)
1. Q. What is meant by matter?
Ans: Anything that has mass and occupies space is called matter. For example: sugar, salt, etc.
2. Q. Write the differences between homogeneous and heterogeneous mixtures.
Ans: (i) In a homogeneous mixture, the composition is uniform throughout. For example: a mixture of salt and water.
On the other hand, in a heterogeneous mixture, the composition is not uniform throughout. For example: a mixture of chalk powder and potassium permanganate.
(ii) A homogeneous mixture is generally transparent.
On the other hand, a heterogeneous mixture is not transparent.
Answers to Questions Within the Lesson(2)
1. Q. Write the differences between homogeneous and heterogeneous mixtures with examples.
Ans: In a homogeneous mixture, the composition is uniform throughout and its components cannot be distinguished separately. For example: salt solution. In a heterogeneous mixture, the composition is not uniform and its components can be distinguished separately. For example: a mixture of sand and water.
2. Q. What are the differences between colloid, solution and suspension?
Ans: A solution is a homogeneous mixture in which the solute particles are very small and do not scatter light. A suspension is a heterogeneous mixture in which the particles are large enough to settle down and scatter light. A colloid has an intermediate particle size; it appears homogeneous but is actually heterogeneous and shows the Tyndall effect.
3. Q. At 293 K, 36 g of sodium chloride is dissolved in 100 mL of water to obtain a saturated solution. Find the concentration of the solution.
Ans: Concentration = (Mass of solute / Volume of solution) × 100= (36 g / 100 mL) × 100
= 36 g per 100 mL or 36% (w/v)
Answers to Questions Within the Lesson(3)
1. Q. How will you separate a mixture of kerosene and petrol (difference in boiling points is more than 25°C)?
Ans: A mixture of kerosene and petrol can be separated by the process of simple distillation.
The mixture is taken in a distillation flask and heated. On heating, petrol vaporizes first due to its lower boiling point. The vapour passes through the condenser where it cools and condenses into liquid, which is collected in receiver. After petrol is separated, kerosene remains in the flask.
2. Q. Name the methods of separation for the following mixtures.
(a) Butter from curd.
(b) Salt from sea water.
(c) Camphor from salt.
Ans: (a) Centrifugation.
(b) Evaporation.
(c) Sublimation.
Q. What type of mixtures can be separated by crystallization?
Ans: Homogeneous mixtures can be separated by crystallization. For example: separation of pure crystals from a solution of copper sulphate or salt solution.
Answers to Questions Within the Lesson(4)
1. Q. Classify the following as chemical or physical changes.
Cutting of trees.
Melting of butter in a pan.
Rusting of iron in an almirah.
Boiling of water to form steam.
Passing electricity through water producing hydrogen and oxygen gases.
Dissolving salt in water.
Preparing salad from raw fruits.
Burning of paper and wood.
Ans:
Chemical changes: Rusting of iron, decomposition of water into hydrogen and oxygen by electricity, burning of paper and wood.
Physical changes: Cutting of trees, melting of butter, boiling of water, dissolving salt in water, preparation of salad.
2. Q. Try to classify the substances around you as pure substances and mixtures.
Ans: Pure substances: Gold, silver, water, sugar, salt, etc.
Mixtures: Air, muddy water, brass, soil, sugar solution, etc.
Exercise: Questions and Answers
1. Q. Which separation methods will you apply to separate the following substances?
(a) Sodium chloride from a solution of salt and water.
(b) Ammonium chloride from a mixture of sodium chloride and ammonium chloride.
(c) Small pieces of metal from car engine oil.
(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) Husk from wheat grains.
(j) Fine particles of mud from a suspension of mud and water.
Ans:
(a) Evaporation method.
(b) Sublimation method.
(c) Filtration method.
(d) Chromatography method.
(e) Centrifugation method.
(f) Separating funnel method.
(g) Filtration method.
(h) Magnetic separation method.
(i) Winnowing method.
(j) Sedimentation and decantation method.
2. Q. Write the steps required to prepare a cup of tea. Use the terms solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Ans: The steps required to prepare tea are as follows—
(i) Take two to three cups of water in a pan and heat it.
(ii) When the water starts boiling, add milk as the solvent and sugar as the solute. Stir with a spoon to dissolve the sugar. Thus, a solution is formed.
(iii) Then add the required amount of tea leaves and boil again. Tea leaves are insoluble in the solution.
(iv) Now filter the solution. The liquid obtained is the filtrate (tea), and the tea leaves left behind are the residue.
3. Q. Pragya tested the solubility of three different substances at different temperatures and recorded the data in a table (data not provided here).
(a) How many grams of potassium nitrate should be dissolved in 50 g of water at 313 K to prepare a saturated solution?
Ans: The exact value depends on the data table. From standard NCERT data, approximately 31–32 g of potassium nitrate dissolves in 50 g of water at
313 K.
(b) At 353 K, Pragya prepared a saturated solution of potassium chloride and allowed it to cool to room temperature. What would she observe? Explain.
Ans: On cooling, some of the dissolved potassium chloride will crystallize out of the solution because solubility decreases with decrease in temperature.
(c) Determine the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
Ans: The exact values depend on the given table. Generally, potassium nitrate shows high solubility, but at 293 K, sodium chloride usually has relatively stable and significant solubility.
(d) Explain the effect of temperature on the solubility of salts.
Ans: The solubility of most solid salts in water increases with an increase in temperature. However, the rate of increase varies for different salts.
4. Q. Explain with examples—
(a) Saturated solution.
Ans: When no more solute can be dissolved in a given amount of solvent at a particular temperature, the solution is called a saturated solution.
(b) Pure substance.
Ans: A substance made up of only one kind of particles is called a pure substance. Pure substances have fixed melting and boiling points. For example, pure ice melts at 0°C and pure water boils at 100°C under standard conditions.
(c) Colloid.
Ans: A colloid is a mixture in which the particle size is intermediate between that of a solution and a suspension. The particles cannot be seen with the naked eye. For example: milk, ink, blood.
(d) Suspension.
Ans: A suspension is a heterogeneous mixture in which the particles are large enough to be seen with the naked eye and settle down on standing. For example: mixture of chalk and water, muddy water.
5. Q. Classify the following mixtures as homogeneous or heterogeneous—
Soda water, wood, air, soil, vinegar, filtered tea.
Ans: Homogeneous mixtures: soda water, air, vinegar, filtered tea.
Heterogeneous mixtures: wood, soil.
6. Q. How will you prove that a given colourless liquid is pure water?
Ans: To prove that a liquid is pure, the following activities should be performed—
(i) Filter the colourless liquid using fine filter paper. If no residue remains on the filter paper, the liquid may be considered pure water.
(ii) Heat the colourless liquid in a container. If no residue is left after complete evaporation, it can be considered pure water.
7. Q. Which of the following substances will fall under the category of“pure substances”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air
Ans: The pure substances are—
(a) Ice, (c) Iron, (d) Hydrochloric acid,
(e) Calcium oxide, (f) Mercury.
8. Q. Select the solutions from the following mixtures—
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Ans: The solutions are— (b) Sea water, (c) Air, (e) Soda water.
9. Q. Which of the following shows the “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
Ans: (b) Milk and (d) starch solution.
10. Q. 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
Ans:
Elements: (a) Sodium, (d) Silver, (f) Tin, (g) Silicon.
Compounds: (e) Calcium carbonate, (k) Methane, (l) Carbon dioxide.
Mixtures: (b) Soil, (c) Sugar solution, (h) Coal, (i) Air, (j) Soap, (m) Blood.
11. Q. Which of the following are chemical changes?
(a) Growth of plants
(b) Rusting of iron
(c) Mixing iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle
Ans: The chemical changes are— (a) Growth of plants, (b) Rusting of iron, (d) Cooking of food, (e) Digestion of food, (g) Burning of a candle.
Additional Questions & Answers
1. Q. What is a mixture? Give examples.
Ans: A mixture is a substance formed by combining two or more substances physically. For example: mixture of sugar and sand, milk, etc.
2. Q. What is a pure substance? Give examples.
Ans: A substance made up of only one kind of component is called a pure substance. For example: copper, silver, gold, etc.
3. Q. Define homogeneous and heterogeneous mixtures.
Ans: A mixture whose composition is uniform throughout is called a homogeneous mixture.
A mixture whose composition is not uniform throughout is called a heterogeneous mixture.
4. Q. What is a solution? Give examples.
Ans: A homogeneous mixture of two or more substances is called a solution. For example: lemonade, soda water, etc.
5. Q. What is an alloy? Give examples.
Ans: An alloy is a mixture of two or more metals or a metal and a nonmetal. For example: brass (copper and zinc), steel (iron and carbon).
6. Q. What are the components of a solution?
Ans: A solution has two components: solvent and solute.
7. Q. Write the properties of a solution.
Ans: The properties of a solution are—
(i) A solution is a homogeneous mixture.
(ii) The particles of a solution are very small and cannot be seen with the naked eye.
(iii) The solute and solvent cannot be separated by filtration.
(iv) The particles do not scatter light.
8. Q. Write the properties of a colloidal solution.
Ans: The properties of a colloidal solution are—
(i) It is a heterogeneous mixture.
(ii) The particles are very small and cannot be seen with the naked eye.
(iii) The particles scatter light (Tyndall effect).
(iv) The colloid is stable.
9. Q. Ink is a mixture of which substances?
Ans: Ink is a mixture of water and colouring substances (dyes/pigments).
10. Q. Write the uses of the centrifugation method.
Ans: The uses of centrifugation are—
(i) Used in diagnostic laboratories to test blood and urine.
(ii) Used in dairies and homes to separate butter from cream.
(iii) Used in washing machines to remove water from wet clothes.
11. Q. Write the uses of chromatography.
Ans: The uses of chromatography are—
(i) Separation of coloured pigments.
(ii) Separation of drugs from blood.
(iii) Separation of pigments obtained from natural sources.
12. Q. What are physical and chemical changes? Give examples.
Ans: A physical change is one in which only the state of a substance changes without changing its properties. For example: water freezing into ice.
A chemical change is one in which the properties of a substance change.
For example: rusting of iron.
13. Q. What is an element? Into how many types is it classified?
Ans: An element is a substance made up of only one kind of atoms. It is classified into three types—
(i) Metals, (ii) Non-metals, (iii) Metalloids.
14. Q. Write the properties of metals and non-metals with examples.
Ans:
Properties of metals—
(i) Metals are lustrous.
(ii) They are generally silver, grey or golden in colour.
(iii) They are good conductors of heat and electricity.
(iv) They are malleable.
(v) They are ductile.
(vi) Examples: gold, silver, copper, sodium, potassium.
Properties of non-metals—
(i) Non-metals show a variety of colours.
(ii) They are poor conductors of heat and electricity.
(iii) They are not lustrous, malleable or ductile.
(iv) Examples: hydrogen, oxygen, iodine, carbon, chlorine, bromine.
15. Q. What is a compound?
Ans: A compound is a substance formed when two or more elements chemically combine in a fixed proportion.
Multiple Choice Questions (MCQ)
1. What is matter?
(a) Anything that has no mass
(b) Anything that occupies space only
(c) Anything that has mass and occupies space
(d) Only liquids and gases
Ans: (c)
2. Which of the following is a pure substance?
(a) Air
(b) Milk
(c) Iron
(d) Soil
Ans: (c)
3. Which of the following is a mixture?
(a) Oxygen
(b) Water
(c) Sugar
(d) Air
Ans: (d)
4. A homogeneous mixture is one in which—
(a) Components are visible
(b) Composition is uniform
(c) Components settle down
(d) Particles are large
Ans: (b)
5. Which of the following is a heterogeneous mixture?
(a) Salt solution
(b) Air
(c) Sand and water
(d) Sugar solution
Ans: (c)
6. Which of the following shows Tyndall effect?
(a) Salt solution
(b) Sugar solution
(c) Milk
(d) Copper sulphate solution
Ans: (c)
7. A solution is—
(a) Heterogeneous mixture
(b) Homogeneous mixture
(c) Pure substance
(d) Suspension
Ans: (b)
8. Which of the following is a colloid?
(a) Salt water
(b) Milk
(c) Sand in water
(d) Sugar solution
Ans: (b)
9. Which of the following is a suspension?
(a) Milk
(b) Sugar solution
(c) Chalk in water
(d) Salt solution
Ans: (c)
10. The particles of a solution are—
(a) Visible to naked eye
(b) Very large
(c) Very small
(d) Settled at bottom
Ans: (c)
11. Which method is used to separate butter from curd?
(a) Filtration
(b) Evaporation
(c) Centrifugation
(d) Sublimation
Ans: (c)
12. Which method is used to separate salt from sea water?
(a) Filtration
(b) Evaporation
(c) Decantation
(d) Chromatography
Ans: (b)
13. Which method is used to separate camphor from salt?
(a) Filtration
(b) Evaporation
(c) Sublimation
(d) Centrifugation
Ans: (c)
14. Which method is used to separate immiscible liquids?
(a) Filtration
(b) Distillation
(c) Separating funnel
(d) Chromatography
Ans: (c)
15. Which process is used to separate components based on boiling points?
(a) Filtration
(b) Distillation
(c) Sedimentation
(d) Winnowing
Ans: (b)
16. Which of the following is an example of a physical change?
(a) Burning paper
(b) Rusting iron
(c) Melting ice
(d) Cooking food
Ans: (c)
17. Which of the following is a chemical change?
(a) Boiling water
(b) Freezing water
(c) Burning wood
(d) Dissolving sugar
Ans: (c)
18. Which of the following is an element?
(a) Water
(b) Air
(c) Gold
(d) Milk
Ans: (c)
19. Which of the following is a compound?
(a) Oxygen
(b) Hydrogen
(c) Carbon dioxide
(d) Air
Ans: (c)
20. Which of the following is a mixture?
(a) Sodium chloride
(b) Water
(c) Air
(d) Carbon dioxide
Ans: (c)
21. What is the solvent in salt solution?
(a) Salt
(b) Water
(c) Sugar
(d) Air
Ans: (b)
22. What is the solute in salt solution?
(a) Water
(b) Salt
(c) Air
(d) Milk
Ans: (b)
23. A saturated solution is one in which—
(a) No solute is present
(b) Maximum solute is dissolved
(c) Minimum solute is dissolved
(d) Solute settles down
Ans: (b)
24. Which of the following increases solubility of solids in liquids?
(a) Decreasing temperature
(b) Increasing temperature
(c) Stirring only
(d) Decreasing pressure
Ans: (b)
25. Which of the following is not a pure substance?
(a) Oxygen
(b) Nitrogen
(c) Air
(d) Iron
Ans: (c)
26. Which of the following can be separated by filtration?
(a) Salt solution
(b) Sugar solution
(c) Sand and water
(d) Milk
Ans: (c)
27. Which of the following is used to separate dyes from ink?
(a) Filtration
(b) Distillation
(c) Chromatography
(d) Sublimation
Ans: (c)
28. Which of the following is a property of colloids?
(a) Particles settle down
(b) Do not scatter light
(c) Scatter light
(d) Particles are visible
Ans: (c)
29. Which of the following is a property of suspension?
(a) Homogeneous
(b) Stable
(c) Particles settle down
(d) Transparent
Ans: (c)
30. Which of the following is an alloy?
(a) Oxygen
(b) Brass
(c) Water
(d) Sugar
Ans: (b)
31. Brass is a mixture of—
(a) Copper and zinc
(b) Iron and carbon
(c) Gold and silver
(d) Copper and iron
Ans: (a)
32. Steel is a mixture of—
(a) Copper and zinc
(b) Iron and carbon
(c) Aluminium and copper
(d) Iron and gold
Ans: (b)
33. Which of the following is a non-metal?
(a) Iron
(b) Copper
(c) Oxygen
(d) Aluminium
Ans: (c)
34. Which of the following is a metal?
(a) Oxygen
(b) Nitrogen
(c) Copper
(d) Chlorine
Ans: (c)
35. Which of the following is a metalloid?
(a) Iron
(b) Oxygen
(c) Silicon
(d) Gold
Ans: (c)
36. Which method is used to separate grains from husk?
(a) Filtration
(b) Winnowing
(c) Distillation
(d) Sublimation
Ans: (b)
37. Which of the following is an example of solution?
(a) Sand and water
(b) Milk
(c) Salt water
(d) Oil and water
Ans: (c)
38. Which of the following is immiscible in water?
(a) Salt
(b) Sugar
(c) Oil
(d) Copper sulphate
Ans: (c)
39. Which process involves settling down of heavier particles?
(a) Filtration
(b) Sedimentation
(c) Distillation
(d) Chromatography
Ans: (b)
40. Which process is used after sedimentation to separate liquid?
(a) Filtration
(b) Decantation
(c) Distillation
(d) Sublimation
Ans: (b)
