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

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.

Question -1 Convert the following temperature to the Celsius scale.

(a) 293 K (b) 470 K

Answer: - (a) Temperature in Celsius scale = Temperature in Kelvin scale - 273

⇒ 293 K = 293 K – 273 = 20⁰C

Answer:- (b) Temperature in Celsius scale = Temperature in Kelvin scale - 273

⇒ 470 K = 470 K – 273 = 197⁰C

Question – 2 - Convert the following temperature to the Kelvin scale.

(a) 25⁰C (b) 373⁰C

Answer: (a) Temperature in Kelvin scale = Temperature in Celsius scale + 273

= 25⁰C + 273 = 298 K

Answer: (b) Temperature in Kelvin scale = Temperature in Celsius scale + 273

= 373⁰C + 273 = 646 K

Question – 3 - Give reason for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.

Answer: Naphthalene ball is a sublimate and a sublimate turns into vapour without changing into liquid. Thus, naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several meters away.

Answer : Perfume turns into gas at room temperature. The vapour of perfume travels up to several meters because of diffusion. That’s why we can get the smell of perfume sitting several meters away.

Question : 4 - Arrange the following substances in increasing order of forces of attraction between the particles – Water, Sugar, Oxygen.

Answer - Oxygen < Water < Sugar

Explanation: Oxygen is a gas, thus force of attraction is negligible between particles. Water is a liquid, thus force of attraction between particles is more than liquid and less than solid. Sugar is a solid, thus force of attraction between particles is greatest.

Question – 5 - What is the physical state of water at –

(a) 25⁰C (b) 0⁰C (c) 100⁰C

Answer: (a) At 25⁰C – water is in liquid state.

(b) At 0⁰C – water is in solid state.

At 100⁰C – water is in transition state, i.e. in liquid and gas both.

Question – 6 - Give two reasons to justify –

(a) Water at room temperature is a liquid.

Answer:

At room temperature:

(i) Water has definite volume, but not definite shape as it takes the shape of the container in which it is kept.

(ii) Water flows at room temperature.

(b) An iron almirah is a solid at room temperature.

Answer:

An iron almirah is a solid at room temperature because:

(i) It has definite shape.

(ii) It has definite volume.

Question : – 7 - Why is ice at 273K more effective in cooling than water at the same temperature.

Answer: At 273K ice requires more latent heat to melt into water, while water at 273K requires less latent heat; to come to the room temperature. So, ice at 273 K is more effective in cooling than water at the same temperature.

Question : – 8 - What produces more severe burns, boiling water or steam?

Answer - Steam produces more severe burns than boiling water, because steam has more latent heat than boiling water.

Question : – 9 - Name A,B,C,D,E and F in the following diagram showing change in its state.

Answer -

A – Heating - Melting

B – Heating - Vapourisation

C – Cooling – Condensation - Liquefaction

D – Cooling – Freezing

E – Sublimation

F – Solidification

Question:- 1. Which one of the following sets of phenomena would increase on raising the temperature?

(a) Diffusion, evaporation, compression of gases

(b) Evaporation, compression of gases, solubility

(c) Evaporation, diffusion, expansion of gas

(d) Evaporation, solubility, diffusion, compression of gasses

Answer - (c) Evaporation, diffusion, expansion of gas

Question:- 2. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions

(a) Low temperature, low pressure

(b) High temperature, low pressure

(c) Low temperature, high pressure

(d) High temperature, high pressure

Answer - (c) Low temperature, high pressure

Question: -The property to flow is unique to fluids. Which one of the following statements is correct?

(a) Only gases behave like fluids

(b) Gases and solids behave like fluids

(c) Gases and liquids behave like fluids

(d) Only liquids are fluids

Answer (c) Gases and liquids behave like fluids

Question: -4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of

(a) diffusion

(b) transpiration

(c) osmosis

(d) evaporation

Answer (d) Evaporation

Question: -5 -A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?

(a) Water, air, wind

(b) Air, sugar, oil

(c) Oxygen, water, sugar

(d) Salt, juice, air

Answer (c) Oxygen, water, sugar

Question: -6 -On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be

(a) 298 K, 311 K and 339 K

(b) 298 K, 300 K and 338 K

(c) 273 K, 278 K and 543 K

(d) 298 K, 310 K and 338 K

Answer (a) 298 K, 311 K and 339 K

Question: - 7. Choose the correct statement of the following

(a) conversion of solid into vapours without passing through the liquid state is called vapourisation.

(b) conversion of vapours into solid without passing through the liquid state is called sublimation.

(c) conversion of vapours into solid without passing through the liquid state is called freezing.

(d) conversion of solid into liquid is called sublimation.

Answer - (b) conversion of vapours into solid without passing through the liquid state is called sublimation.

Question: -8 -The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale?

(a) 306 K, 329 K, 391 K

(b) 308 K, 329 K, 392 K

(c) 308 K, 329 K, 391 K

(d) 329 K, 392 K, 308 K

Answer - (c) 308 K, 329 K, 391 K

Question: -9 -. Which condition out of the following will increase the evaporation of water?

(a) Increase in temperature of water

(b) Decrease in temperature of water

(c) Less exposed surface area of water

(d) Adding common salt to water

Answer - (a) Increase in temperature of water

Question: -10 -In which of the following conditions, the distance between the molecules of hydrogen gas would increase?

(i) Increasing pressure on hydrogen contained in a closed container

(ii) Some hydrogen gas leaking out of the container

(iii) Increasing the volume of the container of hydrogen gas

(iv) Adding more hydrogen gas to the container without increasing the volume of the container

(a) (i) and (iii)

(b) (i) and (iv)

(c) (ii) and (iii)

(d) (ii) and (iv)

Answer - (c) (ii) and (iii)

Question: -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.

Question: -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:

Question: - (a) Evaporation of a liquid at room temperature leads to a __________ effect.

Answer - Cooling

Question: - (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

Question: - (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

Question: -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:

 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.

Question: - 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

Question: -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.

Question: -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.