CBSE Class 9 Science Matter in our sorroundings Sure Shot Questions Set 01

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ASSIGNMENT QUESTIONS SET – 1

CHAPTER – 1

MATTER IN OUR SURROUNDINGS

Fill in the blanks

The process of ________ causes cooling.

Answer: Evaporation

The process of cooling glass is known as ____.

Answer: Annealing

Liquids have no fixed ______ but have fixed _____.

Answer: Shape; volume

____ exists in all three states of matter.

Answer: Water

Carbon dioxide is a white solid called _____ at temperatures below ______.

Answer: Dry ice; −78 °C (195 K)

State True or False

Evaporation of water is a bulk phenomenon.

Answer: False. Evaporation is a surface phenomenon; boiling is a bulk phenomenon.

Diffusion takes place in a haphazard and random way.

Answer: True.

The SI unit of pressure is the pascal.

Answer: True.

A gas is a highly incompressible fluid.

Answer: False. A gas is highly compressible.

Solids and liquids can be identified from their characteristic melting and boiling points.

Answer: True.

Multiple choice questions

Zig-zag movement of the solute particles in a solution is known as

1. Linear motion
2. Circular motion
3. Brownian motion
4. Curved motion

Answer: (c) Brownian motion

Gases can be liquefied by

1. increasing pressure
2. decreasing temperature
3. both (a) and (b)
4. decreasing pressure

Answer: (c) both (a) and (b)

Density of a substance is defined as

1. ratio of mass and volume
2. product of mass and volume
3. ratio of mass and temperature
4. product of mass and temperature

Answer: (a) ratio of mass and volume

Which of the following is not matter?

1. Blood
2. Humidity
3. Electron
4. Moon rock

Answer: All four options are matter, so the question is faulty as printed. The nearest intended answer is (b) humidity, which is only water vapour in air, but strictly it is also matter.

Which is more effective in cooling?

1. Ice at 0 °C
2. Water at 0 °C
3. Water at 100 °C
4. Ice at 100 °C

Answer: (a) Ice at 0 °C, because it absorbs the latent heat of fusion to melt. (Ice cannot exist at 100 °C.)

0 °C temperature is equal to

1. 0 K
2. 273 K
3. −273 K
4. 300 K

Answer: (b) 273 K

The process involving the change of state from solid to gas is called

1. melting
2. boiling
3. sublimation
4. fusion

Answer: (c) sublimation

A solid has

1. definite volume and no definite shape
2. no definite volume, no definite shape
3. definite shape and volume
4. definite shape but no definite volume

Answer: (c) definite shape and volume

A liquid has

1. definite volume and no definite shape
2. no definite volume, no definite shape
3. definite shape and volume
4. definite shape but no definite volume

Answer: (a) definite volume and no definite shape

A gas has

1. definite volume and no definite shape
2. no definite volume, no definite shape
3. definite shape and volume
4. definite shape but no definite volume

Answer: (b) no definite volume and no definite shape

Which of the following is NOT a property of the particles of matter?

1. The particles of matter are extremely small
2. The particles of matter have spaces between them
3. The particles of matter are in a stationary state
4. The particles of matter attract each other

Answer: (c) The particles of matter are in a stationary state. They are always moving.

Which of the following has minimum spaces among the particles?

1. Solids
2. Liquids
3. Gases
4. None of these

Answer: (a) Solids

During summer, water kept in an earthen pot becomes cool because of the phenomenon of

1. diffusion
2. transpiration
3. osmosis
4. evaporation

Answer: (d) evaporation

The rate of diffusion is the fastest in

1. solids
2. liquids
3. gases
4. None of these

Answer: (c) gases

Thermal conduction takes place in

1. solids only
2. liquids only
3. gases only
4. solids, liquids and gases

Answer: (d) solids, liquids and gases

Evaporation always causes

1. thermal expansion
2. liquefaction
3. cooling down
4. all of these

Answer: (c) cooling down

A change of state directly from solid to gas without changing into the liquid state (or vice versa) is called

1. evaporation
2. sublimation
3. diffusion
4. condensation

Answer: (b) sublimation

The rate of evaporation decreases with

1. increase in humidity
2. increase of temperature
3. increase in wind speed
4. increase of surface area

Answer: (a) increase in humidity

Short and long answer questions

Expand CNG and LPG.

Answer: CNG is compressed natural gas. LPG is liquefied petroleum gas.

Arrange the following substances in increasing order of force of attraction between the particles: (i) milk (ii) salt (iii) oxygen.

Answer: Oxygen < milk < salt.

Why is a sponge a solid though it is compressible?

Answer: A sponge has a definite shape and volume and it keeps its shape when left alone. It has tiny holes (spaces) filled with air, which gets squeezed out on pressing, so it can be compressed.

Write one important characteristic of matter.

Answer: Matter is made up of very small particles with spaces between them. (Matter has mass and occupies space.)

Why does a desert cooler cool better on a hot, dry day?

Answer: On a hot, dry day the rate of evaporation of water is higher because the temperature is high and the humidity is low. More evaporation takes away more heat, so the cooling is better.

Convert: (a) 25 °C into the kelvin scale; (b) 500 K into the Celsius scale.

Answer: (a) K = °C + 273 = 25 + 273 = 298 K.
(b) °C = K − 273 = 500 − 273 = 227 °C.

Why does the smell of hot sizzling food reach you several metres away, but to get the smell from cold food you have to go close?

Answer: The particles of hot food have more kinetic energy, so they diffuse faster and reach us from far away. The particles of cold food move slowly, so they diffuse only a short distance.

What is the term used for the change of solid state to liquid state?

Answer: Melting (fusion).

Name the temperature at which the solid and liquid states of matter can coexist.

Answer: The melting point.

Define evaporation.

Answer: Evaporation is the change of a liquid into vapour at any temperature below its boiling point. It is a surface phenomenon.

"The wool being knitted into a sweater is a physical change." Justify the statement.

Answer: The shape of the wool changes, but no new substance is formed and the wool keeps its chemical properties. A change in which no new substance is formed is a physical change.

Mention two ways to liquefy atmospheric gases.

Answer: By applying pressure (compressing the gas) and by lowering the temperature (cooling it).

What is the value of the boiling point of water on the Kelvin scale?

Answer: 373 K.

What is dry ice?

Answer: Dry ice is solid carbon dioxide. It changes directly from solid to gas on heating, without becoming liquid.

(a) Dry ice is compressed at high pressure. What happens when the pressure is released? (b) Suggest a method to liquefy atmospheric gases.

Answer: (a) When the pressure is released, solid carbon dioxide changes directly into carbon dioxide gas (it sublimes).
(b) Atmospheric gases can be liquefied by increasing the pressure and decreasing the temperature.

(a) The melting points of two substances A and B are 280 K and 320 K respectively. Are these substances liquid at room temperature? Justify your answer. (b) Give an example that shows that the state of matter can be changed into another state by changing the temperature.

Answer: (a) Room temperature is about 298 K (25 °C). A melts at 280 K, which is below room temperature, so A is a liquid at room temperature. B melts at 320 K, which is above room temperature, so B is a solid.
(b) Ice (solid) melts into water (liquid) on heating, and water changes to steam (gas) on further heating.

How will you show that matter is composed of tiny particles?

Answer: Dissolve a crystal of potassium permanganate (or a spoon of sugar) in a beaker of water. The whole water becomes coloured (or sweet), and even a very dilute solution is still coloured. This shows that one crystal breaks into millions of tiny particles, which spread through the water.

Define (i) latent heat of fusion and (ii) latent heat of vaporisation.

Answer: (i) The amount of heat energy required to change 1 kg of a solid into liquid at its melting point, without any rise in temperature, is the latent heat of fusion.
(ii) The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point, without any rise in temperature, is the latent heat of vaporisation.

Explain how the following factors affect the rate of evaporation of a liquid: (i) temperature of the liquid, (ii) area of the exposed surface, (iii) moisture in the surrounding air, (iv) increase in wind speed.

Answer: (i) A higher temperature gives the particles more kinetic energy, so the rate of evaporation increases.
(ii) A larger exposed surface area increases the rate of evaporation.
(iii) If the air already has a lot of moisture (high humidity), the rate of evaporation decreases.
(iv) A higher wind speed carries the vapour away, so the rate of evaporation increases.

When a bottle of scent is opened in one corner of a room, it immediately spreads throughout the room. What property of matter is responsible for this observation? Explain.

Answer: Diffusion. The particles of the scent have spaces between them and are always moving, so they mix with the particles of air and spread throughout the room.

(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) Deposition (also called sublimation of the vapour, or condensation to solid).
(b) The latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into liquid at its melting point, without any rise in temperature.

Both boiling and evaporation convert a liquid into vapours. What is the difference between the two processes?

Answer: Evaporation takes place at any temperature, only from the surface of the liquid, and it causes cooling. Boiling takes place only at the boiling point, throughout the liquid (it is a bulk phenomenon), with bubbles forming inside the liquid.

A sample of water under study was found to boil at 102 °C at normal pressure. Is the water pure? Will this water freeze at 0 °C? Comment.

Answer: Pure water boils at 100 °C at normal pressure. This sample boils at 102 °C, so it contains some dissolved impurity and is not pure. The impurity also lowers the freezing point, so the sample will not freeze at 0 °C but at a temperature slightly below 0 °C.

Why does the temperature of a substance remain constant during its melting point or boiling point?

Answer: The heat supplied is used up in overcoming the force of attraction between the particles to change the state. This heat is the latent heat, so it does not raise the temperature until the change of state is complete.

(i) Arrange the following substances in increasing order of force of attraction between the particles: water, hydrogen, sand. (ii) Why does the temperature remain constant at the melting point? (iii) Which property of gases makes it possible to fill a large volume of gas in small cylinders?

Answer: (i) Hydrogen < water < sand.
(ii) The heat supplied is used to overcome the force of attraction between the particles (latent heat), not to raise the temperature.
(iii) Gases are highly compressible because their particles have large spaces between them.

(a) Why is ice at 273 K more effective in cooling than water at the same temperature? (b) Name the two gases which are supplied in compressed form in homes and hospitals.

Answer: (a) Ice at 273 K absorbs the additional latent heat of fusion from the surroundings to change into water, so it cools more than water at the same temperature.
(b) LPG (liquefied petroleum gas) is supplied in homes and oxygen is supplied in hospitals.

You want to wear your favourite shirt to a party but it is still wet after a wash. What steps would you take to dry it fast?

Answer: Spread the shirt fully so that more surface area is exposed, hang it in the sun or in front of a fan or hot air blower (higher temperature and wind speed), and keep it in a place where the air is dry. All these increase the rate of evaporation.

Give reasons: (a) Steam produces more severe burns than boiling water. (b) We are able to sip hot tea faster from a saucer than from a cup. (c) Water kept in an earthen pot becomes cool during summer.

Answer: (a) Steam has extra heat energy (latent heat of vaporisation) compared with boiling water at the same temperature, so it burns more severely.
(b) In a saucer the tea has a larger surface area, so it evaporates and cools faster.
(c) Water seeps through the tiny pores of the pot and evaporates from the outer surface, which takes heat from the water inside and cools it.

Why do cotton clothes suit best in summer?

Answer: In summer we sweat more. Cotton absorbs sweat and exposes it to the air so that it evaporates quickly, and the evaporation takes heat from the body and keeps us cool.

Classify the following into osmosis and diffusion: (a) swelling up of a resin 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) aquatic animals using oxygen dissolved in water during respiration.

Answer: (a) Osmosis.
(b) Diffusion.
(c) Osmosis.
(d) Osmosis.
(e) Osmosis.
(f) Diffusion.

   (a) Linear motion

   (b) Circular motion

   (d) Curved motion.

4. Gases can be liquified by

   (a) increasing pressure

   (b) decreasing temperature

6. Which of the following is not matter

   (a) Blood

   (c) Electron

   (d) Moon rock

(c) -273 K

(d) 300 K

(a) melting

(b) boiling

(c) fusion

10. A solid has

(a) diffusion

(b) transpiration

(d) None of these

17. Thermal conduction takes places in

(a) solids only

(b) liquids only

(c) gases only

(a) thermal expansion

(b) Liquification

(c) Diffusion

(d) Condensation