ncert question and answers for class 9th
Matter In Our Surroundings
Question : 1 – Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
Answer - Chair, air, almonds, and cold-drink are matters.
Explanation: Things that occupy space and have some mass are called matter. Since chair, air, almonds and cold-drink occupy some space and have some mass, so these are matter.
Question: 2 - Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: Smell of anything comes because of gases emanating from the given thing. The smell reaches to us because of diffusion of gas. The rate of diffusion increases with increase in temperature. This happens because of higher kinetic energy due to higher temperature. That is why smell of hot sizzling food reaches to us from several feet. On the other hand, the kinetic energy of gases emanating from cold food is low because of lower temperature. Due to this, we need to move closer to a cold food to take its smell.
Question: 3 - A diver is able to cut through water in a swimming pool. Which property of mater does this observation show?
Answer: Water is also a matter. We know that particles of matter have space between them. In case of fluids, the space between particles is large enough and due to this it becomes easier for a diver to cut through water in a swimming pool.
Question : 4 - What are the characteristics of the particles of matter?
Answer - Characteristics of the particles of matter:
- The particles of matter are very small.
- The particles of matter have space between them.
- The particles of matter are moving constantly.
- The particles of matter attract one another.
Question : 5 - The mass per unit volume of a substance is called density. (Density = mass / volume) Arrange the following in order of increasing density
air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer - Air < Exhaust from chimneys < cotton < Water < Honey < Chalk < Iron
Explanation:
Air is the mixture of gases. Chimney exhaust is also a mixture of gases; along with some heavier particles, such as ash. This makes the density of chimney exhaust more than air.
Cotton is a porous solid and which has lot of air trapped within pores. This makes its volume more than water. Therefore, it is less dense than water.
Question : – 6 – (a) - Tabulate the differences in the characteristics of states of matter.
Answer:
Question : – 7 – (b) - Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density
Answer:
Rigidity: The greatest force of attraction between particles and close packing of particles make solids rigid. Rigidity is one of the unique properties of solids. Because of rigidity, a solid can resist from getting distorted. Because of rigidity a solid has definite shape and volume. Rigidity is negligible in fluid and gas.
Compressibility: Compressibility is one of the most important characteristics of gas. Because of lot of space between particles, a gas can be compressed to a great extent.
Liquid and solid cannot be compressed because of the least space between their particles.
Fluidity: The ability to flow is called fluidity. The less force of attraction and more space between particles make liquid and gas to flow. That’s why liquid and gas are called fluid.
Filling of a gas container: Liquids do not fill a gas container completely, while gases fill the gas container completely in which it is kept. This is because the particles of gas can move in all the directions.
Shape: Solids have fixed shape. Liquid and gas take the shape of the container in which they are kept. This happens because of less force of attraction and more kinetic energy between particles of liquids and negligible force of attraction and highest kinetic energy between particles of gas.
Kinetic energy: The kinetic energy of particles of solid is the minimum. They only vibrate at their fixed position. The kinetic energy of particles of liquid is more than that of solid. But they can slide above one another. The kinetic energy of particles of gas is the maximum.
Density: The mass per unit volume of a substance is called density. The density of solid is highest, of liquid is less than solid and of gas is minimum.
Question : – 8 - Give reasons
(a) A gas fills completely the vessel in which it is kept.
Answer: The force of attraction between particles of gas is negligible. Because of this, particles of gas move in all directions. Thus, a gas fills the vessel completely in which it is kept.
(b) A gas exerts pressure on the walls of the container.
Answer - Because of negligible force of attraction between particles of gas, the particles of gas have the highest kinetic energy. These properties enable the particles of gas to move in all directions and hit the walls of container from all sides. Because of this a gas exerts pressure on the walls of the container in which it is kept.
(c) A wooden table should be called a solid.
Answer: A wooden table has fixed shape and fixed volume, which are the main characteristics of solid. Thus a wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer: Since, air is gas, so its particles are loosely packed and there is negligible force of attraction between its particles. Because of that we can easily move our hand in air.
But wood is a solid, so the force of attraction between its particles is greatest. The particles of wooden block are closely packed. That’s why we cannot move our hand through a solid block of wood. However a karate expert can exert required pressure to break the great force of attraction of the particles of a solid wooden block.
Question – 9 - Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer: During freezing of water, some space between the particles of water is left vacant with some air trapped between them. These empty spaces having air in them makes the density of ice; lower than that of water. That’s why ice floats on water.
Question : – 10 - Convert the following temperature to Celsius scale.
(a)300 K (b) 573 K
Answer - (a) Temperature on Kelvin scale = Temperature on Celsius scale + 273
Therefore,
Temperature on Celsius scale = Temperature of Kelvin scale – 273
Hence, Temperature on Celsius scale = 300K – 273 = 27⁰C
Answer (b) Temperature on Kelvin scale = Temperature on Celsius scale + 273
Therefore, Temperature on Celsius scale = Temperature of Kelvin scale – 273
Hence, Temperature on Celsius scale = 573K – 273 = 300⁰C
Question : – 11 - What is the physical state of water at
(a) 250⁰C (b) 100⁰C
Answer: (a) Since, water boils at 100⁰C, thus it is in gaseous state at 250⁰C.
Answer: (b) Since, water boils at 100⁰C, thus at 100⁰C water is in transition phase, i.e. in both liquid and gaseous states.
Question : – 12 - For any substance why does the temperature remain constant during the change of state.
Answer: During the change of state of any substance, the heat supplied or released is utilised in phase change. Such heat is called latent heat. So, the temperature of any substance remains constant during the change of state.
Question: 13 - Suggest a method to liquefy atmospheric gas.
Answer - Atmospheric gas is liquefied by increasing pressure and decreasing temperature.
Question : – 14 - Why does a desert cooler cool better on a hot dry day?
Answer - Desert cooler works on the basis of evaporation. In hot and dry days the moisture level is very low in atmosphere which increases the rate of evaporation. Because of faster evaporation, cooler works well. That’s why desert cooler cool better on a hot dry day.
Question : – 15 - How does the water kept in an earthen pot (matka) become cool during summer?
Answer: Water from porous wall of earthen pot evaporates continuously, which lowers the temperature of water kept in the earthen pot.
In summer moisture level is very low in the atmosphere, which increases the rate of evaporation as evaporation is inversely proportional to the moisture level in atmosphere. That is why in summer water kept in earthen pot becomes cool.
Question : – 16 - Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer - When acetone or petrol or perfume is poured over palm, it evaporates quickly as these are volatile liquids. The evaporation lowers the temperature of palm and our palm feels cold.
Question : – 17 – Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer - When hot tea or milk is kept in a saucer, the liquid is exposed over a larger surface area as compared to in case of the liquid being kept in a cup. The larger surface area enables the faster cooling. That’s why we are able to sip hot tea or milk faster from a saucer rather than from a cup.
Question : – 18 - What type of clothes should we wear in summer?
Answer - We should wear cotton cloths in summer. Because cotton cloths are good absorbent and they absorb sweat excreted in summer. Because of evaporation of sweat from the surface of cotton cloth, we feel colder and comfortable.
Short Answer Type Questions
Q -11- A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.
Answer: The boiling point of pure water is 1000C. Soluble impurities increase the boiling point of a liquid.
As the sample of water boils at 1020C, hence it is not pure.
Impurities does not affect the freezing point, hence the given sample of water will freeze at 00C.
Q -12- A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following (Fig. 1.1) would correctly represent the result? Justify your choice.
Answer – Figure (d) represents the result correctly.
Explanation: Initially temperature of the content of beaker does not rise, because of latent heat of fusion. When all ice melts and, the temperature of content starts rising, hence, figure (d) represents the result correctly.
Question -13. Fill in the blanks:
Q - (a) Evaporation of a liquid at room temperature leads to a __________ effect.
Answer - Cooling
Q - (b) At room temperature the forces of attraction between the particles of solid substances are __________ than those which exist in the gaseous state.
Answer - stronger
Q - (c) The arrangement of particles is less ordered in the _________ state. However, there is no order in the _______ state.
Answer - (a) liquid (b) gaseous
(d) _____________ is the change of gaseous state directly to solid state without going through the _____________ state.
Answer - (a) sublimation (b) liquid
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called ___________.
Answer - evaporation
Q -14 - Match the physical quantities given in column A to their S I units given in column B :
Answer
Q - 15 - The non S I and S I units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity:
Answer
Q - 16 -‘Osmosis is a special kind of diffusion’. Comment.
Answer:
The movement of particles from low concentration to high concentration is responsible for the diffusion in liquids and gases. In the case of osmosis the particles move from the low concentration to high concentration through the semi permeable membrane, this happens because of diffusion.
Hence, osmosis is called a special kind of diffusion.
Q - 17. Classify the following into osmosis/diffusion
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked throughout the house.
(g) Aquatic animals using oxygen dissolved in water during respiration.
Answer:
(a) – Osmosis
(b) – Diffusion
(c) – Osmosis
(d) – Osmosis
(e) – Osmosis
(f) – Diffusion
(g) – Diffusion
Q -18. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.
Answer:
Water turns into ice when temperature decreases to 00C. Water turns into steam at 1000C when heat is supplied to water. Water as steam has more latent heat while water as liquid does not. Hence water as steam may cause severe burns while water as ice has a cooling effect.
Q- 19. Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.
Answer:
The boiling point of water is 1000C. The temperature of boiling water does not rise instead of continuous supply of heat, as the extra heat is supplied to the water is used to turn water into steam. Hence, steam has a lot of latent heat which can cause severe burn. That’s why Alka felt intense heat from the puff of steam gushing out of the spout of the kettle.
Q - 20. A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.
Answer: Figure (a).
The temperature of water falls to 00C first. Then it will be constant till all water turn into ice, then it will decrease.
Q -21. Look at Fig. 1.3 and suggest in which of the vessels A, B, C or D the rate of evaporation will be the highest? Explain.
Answer: Figure (c).
The rate of evaporation increases with the increase in surface area and wind speed. The surface areas of vessel C, A and D are similar but the wind speed is greater above the vessel C because of fan, hence the rate of evaporation will be highest in the vessel C.
Q -22. (a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?
Answer:
(a) The conversion of vapour to solid without changing into liquid is known as ‘sublimation’. This process is also known as ‘deposition’.
(b) Latent heat of fusion is the heat required to melt the solid state to liquid state without increase in temperature.
Q - 23. You are provided with a mixture of naphthalene and sodium chloride by your teacher. Suggest an activity to separate them with well labeled diagram.
Answer:
The mixture of naphthalene and sodium chloride can be separated by the process of sublimation as naphthalene is a sublime, i.e. it turns into vapour without changing in liquid and its vapour change into solid without changing into liquid, while sodium chloride is not a sublime.
Activity:
Materials required – China glass, funnel, tripod, gas burner, spatula, cotton.
Process:
• Take the mixture in a china glass.
• Put it on the tripod.
• Cover the mixture with a funnel by putting it inverted on the china glass.
• Plug the tip of the funnel using some cotton.
• Now start heating the china glass containing mixture.
• Stop heating after 30 to 60 second when vapour starts rising in the funnel.
• Leave the apparatus to get cooled.
• You will observe that naphthalene gets deposited on the inner wall of the funnel because of sublimation leaving the sodium chloride in the china glass.
• Scratch out the naphthalene deposited on the inner wall of the funnel.
Using this process the mixture of naphthalene and sodium chloride can be separated.
Q -24. It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?
Answer:
Sweating is a natural mechanism to keep our body cool. Our body sweats a lot in the hot summer days. A cotton cloth absorbs sweat easily, while a nylon cloth does not.
Evaporation of sweat absorbed by cotton cloth resulted in cooling effect to our body. The rate of evaporation also increases with the increase in surface area.
When one wear cotton cloth in hot summer days it absorbs the sweat coming out from our body easily. The surface area of sweat also increases as it is absorbed by the cotton cloth which increases the rate of evaporation and one who wears cotton cloth feels more comfortable because of cooling effect due to evaporation of sweat.
Hence, Priyanshi who wearing cotton cloth will feel more comfortable, while Ali does not.
Q - 25. You want to wear your favourite shirt to a party, but the problem is that it is still wet after a wash. What steps would you take to dry it faster?
Answer:
Wet cloths dried up because of evaporation. The rate of evaporation increases with the increase in temperature, surface area and wind speed.
Hence, keeping the conditions to increase the rate of evaporation in mind, following steps should be taken to get the favourite shirt dried up quickly-
(a) We shirt should be spread up on the wire. This will increase the surface area of wet shirt which will increase the rate of evaporation.
(b) Speedy wind should be supplied to the shirt using a fan which will increase the rate of evaporation.
(c) If it is a day time, arrange the above combination in the sun, so that increase in temperature would increase the rate of evaporation.
(d) If it is not a day time, a hot iron can be used also before hanging the shirt on a wire.
Q - 26 - Comment on the following statements:
(a) Evaporation produces cooling.
Answer:
In the process of evaporation, water molecules get some of the required kinetic energy to overcome the force of attraction between its particles to get escaped from atmospheric temperature and some of the kinetic energy from its neighbouring molecules. Because of getting some of the kinetic energy from neighbouring molecules, the temperature of neighbouring molecules of water decreases which is resulted in cooling effect.
Hence, evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
Answer:
The moisture present in the atmosphere is called humidity. A dry atmosphere can hold more water molecules than a humid atmosphere. Hence, the rate of evaporation of aqueous solution decreases with the increase of humidity and vice versa.
That’s why increase in humidity in the atmosphere decreases the rate of evaporation of an aqueous solution.
(c) Sponge though compressible is a solid.
Answer:
There are lots of pores found in a sponge which are filled with air. When a sponge is compressed the air trapped in the pores expelled out, and when it is released, pores again filled with the air and a sponge comes in its original shape.
Therefore, sponge is compressible because of air trapped in its pores and not because of the space between its particles as happens in the case of gas.
Hence, sponge is a solid instead of it is compressible.
Q - 27 - Why does the temperature of a substance remain constant during its melting point or boiling point?
Answer:
When heat is supplied to a solid, say ice, it starts melting. But temperature does not rise even after continuous supply of heat until all ice melts. The extra heat supplied, is used in melting of ice, which is called latent heat of fusion.
Similarly, when a liquid, say water, starts boiling the temperature of water does not rise instead of continuous supply of heat. The extra heat supplied to the boiling water is used in the vapourisation of water, which is known as latent heat of vapourisation.
That’s why, the temperature of a substance remains constant during its melting or boiling point.
Matter around us (Mixture)
short Answer Type
10. Suggest separation technique(s) one would need to employ to separate the following mixtures.
(a) Mercury and water
Answer: The technique of Filtration
(b) Potassium chloride and ammonium chloride
Answer: Sublimation
(c) Common salt, water and sand
Answer: Sedimentation, decantation, filtration and evaporation
(d) Kerosene oil, water and salt
Answer: First filtration using separating funnel then after, vapourisation.
11. Which of the tubes in Figure given here (a) and (b) will be more effective as a condenser in the distillation apparatus?
Answer: Figure (a) will be more effective, because of containing fractionating column.
12. Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?
Answer: To separate salt from its solution crystallization can also be used.
13. The ‘sea-water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment.
Answer:
Sea water is the mixture of many salts, water and other many impurities. Apart from these many gases are also dissolved in sea water. Because of salt and some other bigger size of impurities sea water is classified as heterogeneous mixture. Because of mixture of several gases in sea water it is also classified as homogeneous mixture.
14. While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). What technique can be employed to get back the acetone? Justify your choice.
Answer: Since, the boiling point of acetone is 56p>0C and boiling point of water is 1000C, and for distillation the minimum difference in temperature should be 2500C. Thus by the process of distillation acetone can be separated.
15. What would you observe when
(a) a saturated solution of potassium chloride prepared at 60°C is allowed to cool to room temperature.
Answer: Since the solution is a saturated solution, and prepared at 60C which is above the room temperature, therefore, while it is allowed to cool at room temperature some of the potassium chloride will settle down at the bottom, because saturation decreases with decrease in temperature.
(b) an aqueous sugar solution is heated to dryness.
Answer: When an aquous solution of sugar is heated to dryness, the sugar will be left behind in the container after the vaporization of water. The sugar left in the container may be charred because of more heating.
(c) a mixture of iron filings and sulphur powder is heated strongly.
Answer: When a mixture of iron filling and sulphur power is heated strongly ferrous sulphide will be formed.
16. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Answer: Particles in colloid is very small compare to that of the suspension. This makes the colloids more stable than suspension.
Because of the larger size of particles they settle down when suspension is left undisturbed. While in the case of colloid they do not settle as the particles are very small.
17. Smoke and fog both are aerosols. In what way are they different?
Answer:
Smoke – Smoke is mixture of gases and can goes to higher altitudes because of having more temperature.
Fog – Fog is mixture of liquid and gases. Fog is settled near the earth surface because of less temperature.
18. Classify the following as physical or chemical properties
(a) The composition of a sample of steel is: 98% iron, 1.5% carbon and 0.5% other elements.
Answer: This is the physical property. Since steel is the alloy and considered as mixture of more than one elements.
(b) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
Answer: This shows the reaction of zinc with hydrochloric acid, hence it is a chemical property.
(c) Metallic sodium is soft enough to be cut with a knife.
Answer: Since, it shows the softness of sodium, thus is a physical property.
(d) Most metal oxides form alkalis on interacting with water.
Answer: This property show the reaction of metal oxides with water, thus a chemical property.
19. The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the desired solution and why?
Answer:
Concentration is the relative percentage of solute compared to the total volume of the solution and it is calculated by dividing mass by volume.
In the case of A, since 50g of NaOH has been dissolved in 100 mL of water, the total volume of solution became about 150 mL, thus concentration of NaOH would be less than 50%.
In the case of B, since 50g of NaOH has been dissolved in 100g of water, therefore, total volume of the solution would become 150 mL, consequently concentration of NaOH would again less than 50%.
In the case of C, 50g of NaOH has been dissolved in water and then volume of the solution made to 100mL, thus concentration of NaOH would become 50%.
Thus, C made the solution of NaOH having concentration equal to 50%.
20. Name the process associated with the following
(a) Dry ice is kept at room temperature and at one atmospheric pressure.
Answer: Since, when dry ice is left at room temperature, it turns into gas, thus this is the process of sublimation.
(b) A drop of ink placed on the surface of water contained in a glass spreads throughout the water.
Answer: When a drop of ink is placed on the surface of water, it spread over the water and finally mixed with water because of the motion of particles, hence this process is diffusion.
(c) A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.
Answer: When potassium permanganate crystals are kept in beaker and water is poured and stirred, the particles of potassium permanganate would mix with water, because of motion of particles, stirring speed up the mixing process, hence this is the process of diffusion.
(d) A acetone bottle is left open and the bottle becomes empty.
Answer: Since acetone vaporizes at room temperature, when a acetone bottle is left open the acetone would vaporize and mix with air, thus this is the process of vaporization.
(e) Milk is churned to separate cream from it.
Answer: While milk is churned, the cream and milk is separated because of centrifugal force, thus this is the process of centrifugation.
(f) Settling of sand when a mixture of sand and water is left undisturbed for some time.
Answer: When mixture of sand and water is left undisturbed, the sand settle at the bottom of water, thus this is the process of sedimentation.
(g) Fine beam of light entering through a small hole in a dark room, illuminates the particles in its paths.
Answer: When fine beam of light entered through a small hole in dark room, because of collision of particles of air and dust, sunbeam illuminates the particles in its path and dust particles are appeared dancing, this happens because of the Tyndall effect.
21. You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample ‘B’ boils at 102°C. Which sample of water will not freeze at 0°C? Comment.
Answer: Since impurities in water raise its boiling point, thus water in sample B is impure. Hence it will not freeze at 00C because of impurities since impAnswer: Since impurities in water raise its boiling point, thus water in sample B is impure. Hence it will not freeze at 00C because of impurities since impurities decreases the freezing point below the 00C, this is the cause that’s why sea water remain liquid below the 00C.
22. What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments? ed with copper or silver for making of ornaments.
Answer: Since, Gold is a highly malleable metal so it is difficult to make the ornaments with pure gold, thus to make its rigidity desiring gold is alloyed with copper or silver for making of ornaments.
23. An element is sonorous and highly ductile. Under which category would you classify this element? What other characteristics do you expect the element to possess?
Answer: Since a metal is sonorous and ductile, thus if an element possesses these qualities this will be kept under the category of metals. The other qualities of metal are good conductor of heat and electricity, lustrous, malleability, etc.
24. Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures
(a) A volatile and a non-volatile component.
Answer: The mixture of acetone and water. In this acetone is volatile and water is non-volatile. The mixture of water and acetone can be separated by the process of distillation.
(b) Two volatile components with appreciable difference in boiling points.
Answer: Mixture of acetone and ethanol. The boiling point of acetone is 560C and that of ethyl alcohol is 78.40C.
The mixture of acetone and ethanol can Answer: Mixture of acetone and ethanol. The boiling point of acetone is 560C and that of ethyl alcohol is 78.40C.
The mixture of acetone and ethanol can be separated using fractional distillation. er are two immiscible liquids, thus their mixture can be separated using separating funnel.
(d) One of the components changes directly from solid to gaseous state.
Answer: The mixture of salt and ammonium chloride. In this mixture ammonium chloride changes from solid to gaseous state directly.
The mixture of salt and ammonium chloride can be separated by the process of sublimation.
(e) Two or more coloured constituents soluble in some solvent.
Answer: The ink is the mixture of dyes of many colours.
The different dyes of ink can be separated using chromatography.
25. Fill in the blanks
(a) A colloid is a __________ mixture and its components can be separated by the technique known as _________.
Answer: heterogeneous, centrifugation
(b) Ice, water and water vapour look different and display different _________ properties but they are ___________ the same.
Answer: Physical, chemically
(c) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of________ and the lower layer will be that of ___________.
Answer: chloroform, water
(d) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called____________.
Answer: Fractional distillation
(e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the _________ of light by milk and the phenomenon is called _________ . This indicates that milk is a ________ solution.
Answer: scattering, Tyndall Effect, colloidal
26. Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Answer: Pure substance, since it contains a single component, i.e. sucrose.
27. Give some examples of Tyndall effect observed in your surroundings?
Answer: Examples of Tyndall Effect:
Sunbeam coming from ventilation. The dust particles present in the way of beam looks luminous because of the scattering of light.
Milk in a glass appearing faint blue, since milk is a colloid and light passes through it scattered.
Sunbeam coming from behind the clouds looks luminous because of the scattering of light.
28. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.
Answer: The mixture of alcohol and water cannot be separated using a separating funnel, since these are not immiscible liquids.
The mixture of alcohol and water can be separated by the process of distillation.
29. On heating calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or a chemical change?
Answer: The conversion of calcium carbonate into calcium oxide and carbon dioxide is a chemical change.
(b) Can you prepare one acidic and one basic solution by using the products formed in the above process? If so, write the chemical equation involved.
Answer: Yes one acidic and one basic solution can be formed by the calcium oxide and carbon dioxide, which are product formed in the above process.
Since metallic oxides are basic and non-metallic oxides are acidic in nature.
Calcium oxide is a metallic oxide. Hence by dissolving it in water a basic solution is formed because of the formation of calcium hydroxide. The reaction involvedCalcium oxide is a metallic oxide. Hence by dissolving it in water a basic solution is formed because of the formation of calcium hydroxide. The reaction involved in this can be written as follows:
CaO + H2O ⇌ Ca(OH)2
Carbon is a non metal hence carbon dioxide is acidic in nature. When it is dissolved in water an acidic solution is formed.
CO2+H2O⇌H2CO3
30. 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.
Answer: Graphite
(b) Name a non-metal which exists as a liquid at room temperature.
Answer: Bromine
(c) The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
Answer: Graphite. Graphite is a good conductor of electricity. It is an allotropic form of carbon.
(d) Name a non-metal which is known to form the largest number of compounds.
Answer: Carbon is a non-metal. It is known to form the largest number of compounds.
(e) Name a non-metal other than carbon which shows allotropy.
Answer: Sulphur is a non-metal which shows allotropy. Disulphur and trisulphur are some of the allotropes of sulphur.
(f) Name a non-metal which is required for combustion.
Answer: Oxygen
31. Classify the substances given in Figure into elements and compounds
Answer:
Elements: Cu, Zn, O2, F2, Hg, Diamond
Compound: CaCO3, NaCl(aq), H2O,
32. Which of the following are not compounds?
(a) Chlorine gas
(b) Potassium chloride
(c) Iron
(d) Iron sulphide
(e) Aluminium
(f) Iodine
(g) Carbon
(h) Carbon monoxide
(i) Sulphur powder
Answer: Chlorine gas, iron, aluminium, iodine, carbon and sulphur powder are not compounds.
Long Answer Type Questions
33. Fractional distillation is suitable for separation of miscible liquids with a boiling point difference of about 25 K or less. What part of fractional distillation apparatus makes it efficient and possess an advantage over a simple distillation process. Explain using a diagram.
Answer:
Apparatus used for fractional distillation has a fractionating column. A simple fractionating column has glass beads in it which provide additional surface area because of which the vapours can spread and cool rapidly. Hence, fractionating column is used to provide the additional surface and to facilitate the cooling of vapour in many cycles.
34. (a) Under which category of mixtures will you classify alloys and why?
Answer:
When constituent particles of a combination of two or more element or compound retains their properties, then it is called mixture. In an alloy the constituent particles, hence alloys are classified as mixture. For example; steel is an alloy of carbon and iron.
(b) A solution is always a liquid. Comment.
Answer: Since, a solution is the homogeneous mixture of two or more substances, thus it is not necessary that a solution would always a liquid.
A solution can be in all the three states of matter. A solution is a homogeneous mixture and can be in all the three states of matter.
Example:
Solution of alcohol in water is a liquid.
Air is a solution of different gas.
Alloy is a solution which is in the form of solid.
(c) Can a solution be heterogeneous?
Answer: Solution is defined as the homogeneous mixture, hence a solution cannot be heterogeneous. But when a mixture becomes heterogeneous, it cannot be fall under the definition of solution.
35. Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly while Part ‘B’ was not heated. Dilute hydrochloric acid was added to both the Parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?
Answer:
Hydrogen gas is released, when dilute hydrochloric acid is added to part ‘A’. Hydrogen gas can be tested by brining a burning matchstick or candle near it. When a burning matchstick is placed near the hydrogen gas, it burns with a pop sound, which is a test for hydrogen gas.
Hydrogen sulphide gas released when dilute hydrochloric acid was added to part ‘B’. Hydrgoen sulphide gas smells like a rotten egg, hence it could be confirmed by its smell.
36. A child wanted to separate the mixture of dyes constituting a sample of in36. A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in Fig. The filter paper was removed when the water moved near the top of the filter paper.
(i) What would you expect to see, if the ink contains three different coloured components?
Answer: Streaks of different colours can be seen on the filter paper.
(ii) Name the technique used by the child.
Answer: Chromatography
(iii) Suggest one more application of this technique.
Answer: Chromatography is used for separating pigments from colours, for the separation drugs from blood sample, etc.
37. A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the lig37. A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the Fig. They were amazed to see that milk taken in the tumbler was Fig.illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it?
(a) Explain why the milk sample was illuminated. Name the phenomenon involved.
Answer: Since, milk is a colloid and when light scattered from the particles of colloids, it is illuminated, thus light was illuminated when passed through the milk. This is known as Tyndall Effect.
(b) Same results were not observed with a salt solution. Explain.
Answer: For scattering of light the size of particles should be large enough. Since the particles of solution are not enough to scattered the beam of light, hence same result were not observed.
(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?
Answer: Soap bubbles and fog are the colloids, hence same effect, i.e. scattering of light is shown by these. This is known as Tyndall effect.
38. Classify each of the following, as a physical or a chemical change. Give reasons.
(a) Drying of a shirt in the sun.
Answer: Drying of shirt in the sun is a Physical change. Since in this change no new substance is formed.
(b) Rising of hot air over a radiator.
Answer: Since, in rising of hot air over a radiator no new substance is formed, hence it is a Physical change.
(c) Burning of kerosene in a lantern.
Answer: While burning of kerosene in a lantern carbon dioxide, and water vapour is formed, hence it is a Chemical change.
(d) Change in the colour of black tea on adding lemon juice to it.
Answer: In this change a new substance is formed, hence it is a Chemical change.
(e) Churning of milk cream to get butter.
Answer: While churning of milk cream to get butter, no new substance is formed, hence it is a Physical change.
39. During an experiment the students were asked to prepare a 10% (Mass/Mass) solution of sugar in water. Ramesh dissolved 10g of sugar in 100g of water while Sarika prepared it by dissolving 10g of sugar in water to make 100g of the solution.
(a) Are the two solutions of the same concentration
Answer: No, the two solutions have different concentrations.
(b) Compare the mass % of the two solutions.
Answer:
We know;
For first solution:
Mass of solute = 10 gram
Mass of solution = 100 gram + 10 gram = 110 gram
Hence;
For second solution:
Mass of solute = 10 gram
Mass of solution = 100 gram
Hence;
Mass percent of first solution: Mass percent of second solution = 9.99: 10
40. You are provided with a mixture containing sand, iron filings, ammonium chloride and sodium chloride. Describe the procedures you would use to separate these constituents from the mixture?
Answer: The given mixture can be separated using the following process.
Magnetic Separation: Using magnetic separation the iron fillings can be separated from the given mixture.
In this a magnet is hover just above the mixture, since iron is a magnetic substance it is attracted by magnet and stuck with it. By this first of all iron fillings are separated.
Sublimation: After the separation of iron fillings, ammonium chloride is separated by the process of sublimation.
Since, ammonium chloride is a sublimate and it turns into vapour directly without changing into liquid, thus when the mixture is sublimated, the ammonium chloride is deposited over the inner wall of funnel leaving the sodium chloride and sand in the watch glass. Ammonium chloride is separated by scratching from the inner wall of the funnel.
Filtration: Now the left mixture of sand and sodium chloride is put in water, after stirring the sodium chloride is dissolved in water. The solution is separated by the process of filtration. The sand left over the filter paper is separated out.
Vapourisation: By the process vaporization, the liquid so obtained is vapouried and crystals of ammonium chloride can be obtained.
Hence, by using the methods of magnetic separation, sublimation, filteration and vapourisation and crystallization the component of given mixture of sand, iron fillings, ammonium chloride and sodium chloride can be separated.
41. Arun has prepared 0.01% (by mass) solution of sodium chloride in water. Which of the following correctly represents the composition of the solutions?
(a) 1.00 g of NaCl + 100g of water
(b) 0.11g of NaCl + 100g of water
(c) 0.0l g of NaCl + 99.99g of water
(d) 0.10 g of NaCl + 99.90g of water
Answer: (c) 0.01 g of NaCl + 99.99 g of water
42. Calculate the mass of sodium sulphate required to prepare its 20% (mass percent) solution in 100g of water?
Answer: In a 20% solution containing 100 g water; the mass percentage of water = 100 – 20 = 80%
Hence; to prepare 20% (w/w) solution in 100 gram of water 25 gram of sodium sulphate is needed.
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