Is Matter Around Us Pure
Class: 9 | Chapter: 2
Extra Questions & Answer
1. How can you change a saturated solution to an unsaturated solution without adding any more solvent to it ?Answer: By increasing the temperature of solution, solubility will increase and hence saturated solution will change into unsaturated solution.
2. Sucrose (sugar) crystals obtained from sugar cane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Answer: It will be a pure substance becouse sucrose obtained from both sources have same chemical composition.
3. Based on which factor a solution is said to be diluted, concentrated or saturated ?
Answer: It is based on amount of solute and solvent .If in a solution amount of solvent is more then it is said to be diluted and if amount of solute is more , the solution is said to be concentrared.
4. Identify solute and solvent in 'tincture of iodine'.
Answer: Tincture of iodine is a solution in which iodine is dissolved in ethanol. So, iodine acts as solute and ethanol acts as solvent.
5. What is mass percent of a solution ?
Answer: Mass percent of a solution = Mass percent of solute / Mass percent of solution × 100
6. What are the two components of a colloidal solution.
Answer: Two components of a colloidal solution are dispersed phase and dispersion medium.
7. In what respect does a true solution differ from a colloidal solution ?
Answer: The main difference between true solution and colloidal solution is their particles size of solute. When the particle size of solute is 0.1 - 1 nm, it is true solution and when the size of particles is 1 - 1000 nm , the solution is colloidal.
8. Two liquids 'A' and 'B' are miscible with each other at room temperature. Which separation technique will you apply to separate the mixture of 'A' and 'B' if the difference in their boiling points is 27°C ?
Answer: Separation depends upon their difference in boiling point. If the difference is less than 25 °C then fractional distillation can be used but here the difference is 27°C so, simple distillation can be used to separate two components.
9. Define crystallisation.
Answer: Crystallisation : The process of formation of solid crystals from liquid or melt.
10. Why is crystallisation technique considered better than simple evaporation to purify solids ?
Answer: Crystallisation technique is better than simple evaporation becouse extent of purity is more in cystallisation and secondly less heating is required in case of crystallisation.
11. Why is water called universal solvent ?
Answer: Water is called universal solvent becouse it dissolves most of the substances than any other liquid.
12. Which of the following are physical changes ?
Melting of iron metal, rusting of iron, bending of iron rod, drawing of a wire of iron metal.
Answer: The physical changes are : melting of iron metal, bending of iron rod, drawing of a wire of iron metal.
13. Name two elements which exist in liquid state at room temperature.
Answer: Bromine and mercury.
14. An unknown substance 'A' on thermal decomposition produces 'B' and 'C'. What is 'A' - an element, a compound or a mixture ?
Answer: A is a compound becouse It gives two or more substances on thermal decomposition.
15. Identify the elements from the following substances ; sulphur, brine, hydrochloric acid, water, neon, paper, sugar.
Answer: Elements are sulphur, neon.
16. 'Sea water can be classified as homogeneous as well as heterogeneous mixture . Comment.
Answer: Sea water is classified as both homogeneous as well as heterogeneous mixture becouse it has both soluble salts and insoluble substances in it.
17. Why is it not possible to distinguish particles of a solute from the solvent in solution ?
Answer: Becouse of the very small size of solute particles, it is not possible to distinguish particles of solute from solvent with naked eyes.
18. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Answer: In case of colloidal solution particles show brownian movement so, they move continously in zig - zag pattern and don't settle down but in case of suspension particles are bigger that's why they settle down when left undisturbed.
19. Identify colloids and true solutions from the following : pond water, fog, aluminium paint, vinegar and glucose solution.
Answer: Colloids: pond water, fog, aluminiun paint
True solution: vinegar, glucose solution
20. What do you understand by the term distillation? Give it's one application.
Answer: Distillation : it is a separation technique which is used to separate two or more than two liquid. It us based on difference in their boiling points.
21. Identify the dispersed phase and dispersing medium in the following colloids.
(a) Fog
(b) Cheese
(c) Coloured gemstone
Answer: Fog: dispersed phase - liquid, dispersing medium - gas
Cheese: dispersed phase - solid, dispersing medium - liquid
Coloured gemstone: dispersed phase - solid, dispersing medium - solid
22. Classify the following into metals, non-metals and metalloids:
(i) Germanium
(ii) Boron
(iii) Diamond
(iv) Iodine
(v) Copper
(vi) Helium
Answer: Metals: Copper
Non - metals: Boron, diamond, iodine, helium
Metalloids: Germanium
23. What is emulsion ?
Answer: Emulsion - It is a type of colloid in which both dispersed phase and dispersion medium are liquids, which generally don't mix with each other. Examples : egg yolk, butter.
24. Give applications of centrifugation ?
Answer: 1. It is used for separation of solid - liquid mixtures e. g. Cream from milk.
2. It is used to collect cells and to precipitate DNA.
3. It is used in washing machines to separate water from clothes.
25. How can you prove that water is a compound ?
Answer: Water is a compound becouse it is made by two elements Hydrogen and Oxygen in a fixed ratio 2 : 1 . It's constituents can't be separated by simple physical processes and water has completely different properties than hydrogen and oxygen .
26. What is the difference in fog and smoke ?
Answer: Fog is the presence of water droplets in air and smog is formed when smoke and fog mix with each other. Smog is a sign of air pollution.
27. If 20g of salt is dissolved in 180g of water. Calculate the concentration of this solution.
Answer: Given, Mass of solute ( Salt) = 20 g
Mass of solvent ( water) = 180 g
Concentration = Mass of solute / Mass of solution × 100
=> Mass of solution - Mass of solute + Mass of solvent = 20 + 180 = 200
Concentration = 20 / 200 × 100 = 10 %
28. Distinguish between physical and chemical changes.
Answer: Physical changes: 1. When there is a change in physical properties like colour, hardness, rigidity, melting point, boiling point, it is assigned as physical change.
2. It is reversible in nature.
3. It is temporary change
Chemical changes: 1. When there is a change in chemical composition, is assigned as chemical change.
2. It is irreversible in nature.
3. It is permanent change.
29. What do you understand by the statement 'the solubility of NaCl is 36.5 g at room temperature'?
Answer: This statement is saying that 36.5 g of NaCl is dissolved in 100 g at room temperature.
30. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.
Answer: No, we can't separate alcohol from water by using seaparating finnel becouse they both are miscible with each other. We need to perform distillation process to seaparate these two. The steps are :
1. Take the mixture in a distillation flask fitted with a thermometer.
2. Heat the mixture slowly, and insert a fractionating colomn.
3. Allow the Vapours to cool down and condense
4. Collect the alcohol from the condenser outlet.
31. How Tyndall effect can be observed in the canopy of a dense forest.
Answer: Tyndall effect can be observed in the canopy of a dense forest when water droplets in the mist act as colloid. So, when sunlight passes through these colloid particles, they scatter the beam of light and make that path visible.
32. What volume of ethyl alcohol and water must be mixed together to prepare 250 ml of 60% by volume of alcohol in water.
Answer: We know, concentration ( percentage by volume ) = Volume of solute ( ethyl alcohol) / volume of solution ( 250 ml) × 100
=> 60 % = volume of ethyl alcohol / 250 × 100
Volume of ethyl alcohol = 150 ml
33. Non-metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
a.Name a lustrous non-metal.
b.Name a non-metal which exists as a liquid at room temperature.
c.The allotropic form of a non – metal is a good conductor of electricity. Name the allotrope.
d.Name a non-metal which is known to form the largest number of compounds.
e.Name a non-metal other than carbon which shows allotrophy.
f.Name a non-metal which is required for combustion.
Answer: a. Iodine
b. Bromine
c. Graphite
d. Carbon
e. Sulphur
f. Oxygen
34. What are aerosols? Give any two examples.
Answer: Aerosols - It is a suspension of fine solid or liquid particles in air or any other gas.
Examples : fog, dust, gyser steam.
35. What is meant by an aqueous and non-aqueous solutions ? Give one example of each.
Answer: Aqueous solutions: It is a solution in which solvent is water. Example : salt in water, sugar in water.
Non - aqueous solutions: It is a solution in which solvent is other than water. Example : iodine in carbon tetrachloride, sulphur in carbon disulphide.
36. What is Tyndall effect? Why the solution of copper sulphate does not show Tyndall effect ?
Answer: Tyndall effect : It is scattering of light beam when passes through a medium containing small suspended particles. Copper sulphate solution doesn't show tyndall effect becouse it is a true solution. Ions present in this solution have size less than 1 nm.
37. What are metalloids? Give two examples.
Answer: Metalloids : An element which has properties intermediate between metals and non - metals. Examples - Boron, Silicon, Antimony.
38. Mention any two differences between heterogeneous and homogeneous mixtures.
Answer: Homogenous mixture: 1. Uniform composition
2. No clear boundaries of separation
Heterogeneous mixture: 1. Non - uniform composition
2. Clear boundary of separation
39. Salt can be recovered from its solution by evaporation. Can you suggest any other technique also.
Answer: The other technique is reverse osmosis. In this, sea water is passed through a permeable filter.
40. State any one difference between pure and impure substances.
Answer: Pure substances have only one type of particles and impure substances have more than one type of particles in them.