Matter In Our Surrounding class 9 CHEMISTRY MCQ & SAQ

Matter In Our Surrounding class 9 CHEMISTRY NCERT SOLUTION:

Q1. What is meant by a substance?

Ans. A pure substance consists of a single type of particle. A substance is a pure single form of matter.

Q2. List the points of differences between homogeneous and heterogeneous mixtures.

Ans.

Q3. Differentiate between homogeneous and heterogeneous mixtures with examples.

Ans.

Q4. How are sol, solution and suspension different from each other?

Ans.​

Q5. To make a saturated solution, 36 g of sodium chloride is dissolved in 100g of water at 293 K. Find its concentration at this temperature.

Ans. Mass of solute (sodium chloride) = 36 g

Q6. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?

Ans. A mixture of kerosene and petrol which are miscible with each other can be separated by distillation.

Method

• Take the mixture in a distillation flask.

• Fit it with a thermometer.

• Arrange the apparatus as shown in the figure.

• Heat the mixture slowly.

• Petrol evaporates first as it has a lower boiling point. It condenses in the condenser and is collected from the condenser outlet.

• Kerosene is left behind in the distillation flask.

Q7. Name the technique to separate (i) butter from curd, (5) salt from sea-water, (iii) camphor from salt.

Ans. (i) Centrifugation, (ii) Evaporation, (iii) Sublimation.

Q8. What type of mixtures are separated by the technique of crystallization?

Ans. Crystallization technique is used to purify solid with some impurities in it. Example: Salt from sea-water

Q9. Classify the following as chemical or physical changes:

• cutting of trees,

• melting butter in a pan,

• rusting of almirah,

• boiling of water to form steam,

• passing of electric current, through water and the water breaking down into hydrogen and oxygen gas,

• dissolving common salt in water,

• making a fruit salad with raw fruits and

• burning of paper and wood.

Ans.​

Physical Change	Chemical Change
cutting of trees	rusting of almirah
melting butter in a pan	passing of electric current through
boiling of water to form steam	water and then breaking down
dissolving common salt in water	into hydrogen and oxygen gas
making a fruit salad with raw fruits	burning of paper and wood

 

Q10. Try segregating the things around you as pure substances or mixtures.

Ans. Pure substances—Water, bread, sugar and gold.

Mixtures—Steel, plastic, paper, talc, milk and air

 

 

Q1. Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.

(c) Small pieces of metal in the engine oil of a car.

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Iron pins from sand.

(i) Wheat grains from husk.

(j) Fine mud particles suspended in water.

Ans. (a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(h) Magnetic separation

(g) Filtration

(e) Centrifugation

(f) Separating funnel

(i) Winnowing/sedimentation

(j) Decantation and filtration.

Q2. Write the steps you would use for making tea. Use the words, solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Ans. 1. Take a cup of water in a container as solvent and heat it.

2. Add sugar , which is a solute. Heat it till all sugar dissolves.

3. You get a solution of water and sugar.

4. Sugar is completely soluble in water.

5. Add half a tea-spoon of tea-leaves, it is insoluble in water.

6. Boil the content, add milk which is also soluble in water, and boil again.

7. Filter the tea with the help of a strainer, the tea collected in the cup is filtrate and the tea leaves collected on the strainer are residue.

Q3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

(d) What is the effect of change of temperature on the solubility of a salt?

Ans. (a) Mass of KNO3 needed to produce a saturated solution of KNO3 in 100 grams of water at 313 K = 62 g

∴ Mass of KNO3 needed in 50 grams of water at 313 K

(b) Crystals of potassium chloride will be obtained on cooling the saturated solution.

(c) Solubility of each salt at 293 K is

(i) Potassium nitrate → 32 g

(ii) Sodium chloride → 36 g

(iii) Potassium chloride → 35 g

(iv) Ammonium chloride → 37 g

Ammonium chloride has the highest solubility at this temperature.

(d) On increasing the temperature, solubility of a salt increases.

Q4. Explain the following giving examples: (a) Saturated solution (b) Pure substance (c) Colloid (d) Suspension

Ans. (a) Saturated solution: In a given solvent when no more solute can dissolve further at a given temperature is called saturated solution.

(b) Pure substance: A pure substance consists of a single type of particles. E.g., gold, silver.

(c) Colloid: A colloid is a solution in which the size of solute particles are bigger than that of a true solution. These particles cannot be seen with our naked eyes, they are stable. e.g., ink, blood.

 (d) Suspension: It is a heterogeneous mixture in which the solute particles are big enough to settle down. e.g., chalk-water, paints, etc.

Q5. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air, soil, vinegar, filtered tea.

Ans. Homogeneous: Soda water, vinegar, filtered tea, air. Heterogeneous: Wood, soil.

Q6. How would you confirm that a colorless liquid given to you is pure water?

Ans. By finding the boiling point of a given colorless liquid. If the liquid boils at 100°C at atmospheric pressure, then it is pure water. This is because pure substances have a fixed melting and boiling point.

Q7. Which of the following materials fall in the category of a “pure substance”? (a) Ice (b) Milk (c) Iron (d) Hydrochloric acid (e) Calcium oxide (f) Mercury (g) Brick (h) Wood (i) Air.

Ans. Pure substances are: Ice, iron, hydrochloric acid, calcium oxide and mercury.

Q8. Identify the solutions among the following mixtures. (a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.

Ans. Solutions are: Sea water, soda water and air.

Q9. Which of the following will show the “Tyndall effect”? (a) Salt solution (b) Milk (c) Copper sulfate solution (d) Starch solution.

Ans. Milk and starch solution.

Q10. Classify the following into elements, compounds and mixtures. (a) Sodium (b) Soil (c) Sugar solution (d) Silver (e) Calcium carbonate (f) Tin (g) Silicon (h) Coal (i) Air (j) Soap (k) Methane (l) Carbon dioxide (m) Blood

Ans.​

Elements	Compounds	Mixtures
Sodium	Calcium carbonate	Sugar solution
Silver	Methane	Soil
Tin	Carbon dioxide	Coal
Silicon	Soap	Air
		Blood

 

Q11. Which of the following are chemical changes?

(a) Growth of a plant

(b) Rusting of iron

(c) Mixing of iron filings and sand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of a candle.

Ans. Chemical changes are:

(a) Growth of a plant

(b) Rusting of iron

(c) Cooking of food

(d) Digestion of food

(e) Burning of a candle

Matter In Our Surrounding class 9 CHEMISTRY MCQ 

Question: As solid melts to form liquid:

• a) All of the above

• b) Inter particle distance increases

• c) Intermolecular forces of attraction decreases

• d) Compressibility increases

Answer: All of the above

 

Question: When we blow air into the balloon it inflates because:

• a) Air particles collide with the walls of the balloon and exert pressure on them

• b) Air particles diffuse into the balloon

• c) Rubber is elastic in nature

• d) The temperature of air in the balloon increases

Answer: Air particles collide with the walls of the balloon and exert pressure on them

 

Question: Particles move randomly in:

• a) Nitrogen

• b) Water

• c) Sugar

• d) Dry ice

Answer: Nitrogen

 

Question: Dry ice on heating produces:

• a) Gas CO2

• b) Liquid CO2

• c) Liquid water

• d) Water vapor

Answer: Gas CO2

 

Question: Which of the following has the highest density?

• a) Iron

• b) Kerosene

• c) Water

• d) Wood

Answer: Iron

 

Question: latent heat of vapourisation is used to:

• a) Overcome forces of attraction between the liquid particles at the boiling point

• b) Overcome forces of attraction between solid particles at the freezing point

• c) Increase the kinetic energy of particles in the liquid state

• d) Increase the kinetic energy of the particles in the vapor phase

Answer: Overcome forces of attraction between the liquid particles at the boiling point

 

Question: which are the favorable conditions for liquefaction of petroleum gas:

• a) High pressure, low temperature

• b) High pressure, high temperature

• c) Low pressure, low temperature

• d) Low pressure, high temperature

Answer: High pressure, low temperature

 

Question: We get the smell of hot food in the kitchen outside the house because of:

• a) Diffusion

• b) Boiling

• c) Evaporation

• d) Sublimation

Answer: Diffusion

 

Question: In which phenomenon does water change into water vapor below its boiling point:

• a) Evaporation

• b) Boiling

• c) Freezing

• d) Sublimation

Answer: Evaporation

 

Question: During evaporation particles of a liquid change into vapors :

• a) From the surface

• b) From the bulk

• c) From the bottom

• d) From all over the liquid

Answer: From the surface

 

 

Question: At higher altitudes the boiling points of liquids

• a) Decreases

• b) Increases

• c) Increases then decreases

• d) Remains the same

Answer: Decreases

Question: Wet clothes are kept for drying. Which of the following does not help them in drying:

• a) Cooling the room

• b) Spreading it out

• c) Blowing wind over it

• d) Making the room a little warmer

Answer: Cooling the room

Question: Which of the following describes a liquid state:

• a) Definite volume and no specific shape

• b) Definite volume and definite shape

• c) definite shape but no definite volume

• d) neither definite shape nor definite volume

Answer: Definite volume and no specific shape

Question: Evaporation of a liquid can take place:

• a) At all temperatures

• b) At its boiling point

• c) At its freezing point

• d) At a fixed temperature

Answer: At all temperatures

Question: The conversion of solid to gas directly is called:

• a) Sublimation

• b) Evaporation

• c) Distillation

• d) Condensation

Answer: Sublimation

Question: The process of evaporation causes:

• a) Cooling

• b) Heating

• c) Dryness

• d) None of the above

Answer: Cooling

Question: Which of the following substances will undergo sublimation?

• a) Odonil

• b) Common salt

• c) Sugar

• d) Sand

Answer: Odonil

Question: Which of the following has highest intermolecular forces of attraction?

• a) Iron metal

• b) Water at room temperature

• c) CO2 gas

• d) Ethyl alcohol

Answer: Iron metal

  

Question: The boiling point of water is:

• a) 101oC at atmospheric pressure

• b) 273K at atmospheric pressure

• c) 0oC at atmospheric pressure

• d) 0K at atmospheric pressure

Answer: 101oC at atmospheric pressure

 

Question: Which of the following is not characteristic of solid:

• a) High compressibility

• b) High Rigidity

• c) Regular Shape

• d) High density

Answer: High compressibility

Question. When a gas jar full of air is placed upside down on a gas jar full of bromine vapors, the red-brown vapors of bromine from the lower jar go upward into the jar containing air. In this experiment:

(a) Air is heavier than bromine

(b) Both air and bromine have the same density

(c) Bromine is heavier than air

(d) Bromine cannot be heavier than air because it is going upwards against gravity

Answer:   C

Question. When water at 0°C freezes to form ice at the same temperature of 0°C, then it:

(a) Absorbs some heat

(b) Releases some heat

(c) Neither absorbs or releases heat

(d) Absorbs exactly 3.34 x 105J/kg of heat

Answer:   B

Question.The evaporation of a liquid can best be carried out in a:

(a) Flask

(b) China dish

(c) Test tube

(d) Beaker

Answer:   B

Question. Zig-zag movement of the solute particle in a solution is known as

(a) Linear motion

(b) Circular motion

(c) Brownian motion

(d) Curved motion.

Answer:   C

Question. CO2 can be easily liquified and even solidified because

(a) It has weak forces of attraction

(b) It has comparatively more force of attraction than other gasses

(c) It has more intermolecular space

(d) It is present in the atmosphere.

Answer:   B

Question. 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 

Question. Which of the following phenomena always results in the cooling effect?

(a) Condensation

(b) Evaporation

(c) Sublimation

(d) None of these

Answer:   B

Question. The color of vapors formed on sublimation of iodine solid is

(a) Purple (violet)

(b) Colorless

(c) Yellow

(d) Orange

Answer:   A

Question..A gas which obeys the gas laws is known as:

(a) An ideal gas

(b) A heavier gas

(c) A lighter gas

(d) A real gas

Answer:   A

Question.What's the term used to describe the phase change as a liquid becomes a solid?

(a) Evaporation

(b) Condensation

(c) Freezing

(d) None of the above

Answer:   C

Question. Which of the following phenomena would increase on raising the temperature?

(a) Diffusion, evaporation, compression of gasses

(b) Evaporation, compression of gasses, solubility

(c) Evaporation, diffusion, expansion of gasses

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

Answer:   C

Question.The quantity of matter present in an object is called its:

(a) Weight

(b) Gram

(c) Mass

(d) Density

Answer:   C

Question.When we put some crystals of potassium permanganate in a beaker containing water, we observe that after sometime the whole water has turned pink. This is due to:

(a) Boiling

(b) Melting of potassium permanganate crystals

(c) Sublimation of crystals

(d) Diffusion

Answer:   D

Question.Which of the following describes the liquid phase?

(a) It has a definite shape and a definite volume

(b) It has a definite shape but not a definite volume

(c) It has a definite volume but not a definite shape

(d) It has neither a definite shape nor a definite volume

Answer:   C

Question.Equal volumes of all gasses under similar conditions of temperature and pressure contain equal numbers of molecules. This statement was made by:

(a) Gay- lussae

(b) Avogadro

(c) Berzelius

(d) John Dalton

Answer:   B

Question. 0 ° C temperature is equal to

(a) 0 K

(b) 273 K

(c)-273 K

(d) 300 K

Answer:   B 

Question.Out of the following which is the densest state of matter?

(a) Solids

(b) Liquids

(c) Gasses

(d) Plasmas

Answer:   A

Question.Rate of diffusion of a gas is:

(a) Directly proportional to its density

(b) Directly proportional to its molecular mass

(c) Inversely proportional to the square root of its density

(d) Inversely proportional to the square root of its molecular mass

Answer:   D

Question. Kinetic energy of molecules is directly proportional to

(a) Temperature

(b) Pressure

(c) Both (a) and (b)

(d) Atmospheric pressure

Answer:   A

Question. 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

Question. Which of the following statements is not true regarding the characteristics of matter?

(a) Particles of a matter are randomly moving in all directions.

(b) Kinetic energy of the particles increases with a rise in temperature

(c) Kinetic energy of the particles of all matters remains the same at a particular temperature.

(d) Particles of matter diffuse into each other on their own.

Answer:   C

Question. Which one is a sublime substance?

(a) Table salt

(b) Sugar

(c) Iodine

(d) Potassium iodide

Answer:   C

Question.: Liquids have -

(a) fixed volume and fixed shape

(b) fixed shape and no fixed volume

(c) fixed volume and no fixed shape

(d) neither fixed volume nor fixed shape

Answer:   C

Question.: When we add sugar in water, particles of sugar disappear because they -

(a) are very small

(b) get into the spaces between water particles

(c) are moving

(d) all above

Answer:   D

Question.: Which of the following substances becomes liquid easily upon heating?

(a) butter

(b) glass

(c) sponge

(d) rubber band

Answer:   A

Question.: Gasses are liquefied under

(a) high pressure, high temperature

(b) high pressure, low temperature

(c) low pressure, high temperature

(d) low pressure, low temperature

Answer:   B

Question.: Which is not the characteristic of matter –

(a) particles of a matter are continuously moving,

(b) particles of matter move faster on increasing temperature,

(c) particles of matter intermix with each other on their own,

(d) particles of all matters have same kinetic energy.

Answer:   D

Matter In Our Surrounding class 9 CHEMISTRY SAQ

 

 

Question 1. Define matter.

Answer: Anything that occupies space and has mass is called matter.

Question 2. State different states of matter with an example.

Answer: Matter has 3 different states

 

Question 3. What is diffusion?

Answer. The intermingling of molecules of one substance with that of the other is called diffusion.

Question 4. What happens to the rate of diffusion if the temperature is increased?

Answer: With increased temperature, the rate of diffusion also increases as the particles gain energy and vibrate more.

Question 5. Name the state of matter that has the tendency to maintain its shape when subjected to outside force.

Answer: Solid.

Question 6. Define melting point.

Answer: The temperature at which a solid melts to become liquid at the atmospheric pressure is called its melting point.

Question 7. Define boiling point.

Answer: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

Question 8. Define latent heat of vaporization.

Answer: Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Question 9. Define latent heat of fusion.

Answer: Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

Question 10. Define sublimation.

Answer: Sublimation is the change of gaseous state directly to solid state without going through liquid state and vice-versa.

Question 11. What is dry ice?

Answer: Solid carbon dioxide obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.

Question 12. What is humidity?

Answer: The air holds water vapor, this air with water is called humid air and the phenomenon is called humidity.

Question.13. Give two properties of solid.

Answer. (1) Solids have fixed shapes and are rigid. (2) Solids cannot be compressed.

Question.14. What will happen if the pressure is reduced on solid carbon dioxide (dry ice)?

Answer. If the pressure is reduced on solid carbon dioxide it will directly change into a gaseous state without melting.

Question 15. dame any three substances that show sublimation.

Answer: Ammonium chloride, camphor and naphthalene balls.

Question 16. Sponge is solid, but we can still compress it. Why?

Answer: Sponge is a solid with minute pores in it. When we press the sponge the air present in these pores is released and hence we are able to compress it.

Question 17. What is normal atmospheric pressure?

Answer: The atmospheric pressure at sea level is 1 atmosphere and taken as the normal atmospheric pressure.

Question 18. What is Kelvin?

Answer: Kelvin is the SI unit of temperature (0°C = 273 K).

Question 19. Give two examples of diffusion.

Answer: Milk drops dissolved in water and perfume sprayed in a room.

Question 20. Give the temperature at which water exists in two different phases/states.

Answer: At 0°C water can be in solid or in liquid state.

At 100°C water can be in liquid or in a gaseous state.

Question 1. Why do we see water droplets collected on the outer surface of a glass container, containing ice?

Answer: The water vapor present in air comes in contact with the cold outer surface of the container thereby condensing it to form water droplets.

Question 2. Explain why solids have fixed shape but liquids and gasses do not have fixed shape.

Answer: Solids have fixed shapes due to the strong intermolecular force of attraction between them. The liquids and gasses have molecules with less intermolecular force of attraction and hence they can flow and take the shape of the container.

Question 3. Liquids and gasses can be compressed but it is difficult to compress solids. Why?

Answer: Liquids and gasses have intermolecular space, on applying pressure externally on them the molecules can come closer thereby minimizing the space between them. But in case of solids there is no intermolecular space to do so.

Question 4. A balloon, when kept in the sun, bursts after some time. Why?

Answer: The balloon has air filled in it. The balloon when kept in the sun gets heated and the air inside it also gets heated. The molecules of air get energy, and vibrate faster thereby exerting large force on the walls of the balloon. Due to this expansion of gasses the balloon bursts.

Question 5. Why do people perspire a lot on a hot humid day?

Answer: On a hot, humid day, due to the heat our body starts sweating for the cooling mechanism i.e., by evaporation and gets a cooling effect. But the air cannot hold any more water on a humid day and therefore sweat or perspiration is seen.

Question 6. Distinguish between evaporation and boiling.

Answer:

Question 7. Why is it advisable to use a pressure cooker at higher altitudes?

Answer: At higher altitudes, the atmospheric pressure is low and the water boils very fast and evaporates at faster rate therefore the pressure is required to increase the cooking process and this is done by using a pressure cooker which increases the pressure inside the container and cooks food faster.

Question 8. What are fluids?

Answer: The states of matter that can flow due to less intermolecular force of attraction, are liquids and gasses and are called as fluids.

Question 9. One kg cotton and one kg sand, which is more denser? Why?

Answer: One kg of sand is more dense than 1 kg of cotton because density = mass/volume .

The volume required by cotton is more than the sand and density and volume are inversely proportional.

Question 10. Why is water liquid at room temperature?

Answer: At room temperature, the molecules of water have some intermolecular force of attraction and the room temperature cannot provide sufficient heat for these molecules to overcome their force of attraction and therefore remain in liquid phase.

Question 11. State the differences between solid, liquid and gas.

Answer:

Question 12. Cotton is solid but it floats on water. Why?

Answer: Cotton has a large number of pores, in which air is trapped. Hence reducing its density and increasing the volume. Therefore cotton floats on water. But when these pores get filled with water it starts sinking.

Question 13. Why are arc solids generally denser than liquids and gasses?

Answer: Density of a substance is given by a formula= Mass/Volume

In case of solids the molecules are tightly packed and hence large mass is concentrated in a very small volume. Hence their density is more. But in the case of liquids and gasses, their molecules have intermolecular space and hence they don’t have large mass concentrated in small volume. So the density of solids is generally more than that of the liquids and gasses.

Question 14. On a hot sunny day, why do people sprinkle water on the roof or open ground?

Answer: During hot sunny days, the surface of roof or ground absorbs large amounts of heat and remains hot, on sprinkling water on these surfaces, the water absorbs large amounts of heat from the surface due to its large latent heat of vaporization thereby allowing the hot surface to cool.

Question 15. On a hot sunny day why do we feel pleasant sitting under a tree?

Answer: Tree has a lot of leaves which constantly show transpiration. Transpiration is loss of water through small tiny pores of leaves called stomata. When this water comes on the surface of the leaf the water evaporates thereby causing a cooling effect. Therefore we feel pleasant sitting under the tree on a hot sunny day.

Question 16. The U’mpeuiUnc at which liquids change into vapor is very high, for example, water evaporates at 100°C then how is it possible for water to evaporate at room temperature or at another temperature?

Answer: The molecules of water present on the surface of the exposed area, which are in very small fraction, gain energy from the surrounding. With this higher kinetic energy they are able to break the force of attraction between them and hence get converted into a vapor state.

This phenomenon of change of a liquid into vapors that takes place at any temperature below its boiling point is called evaporation.

Question 17. Name the factors that affix l evaporation.

Answer: The rate of evaporation will increase with

(1) an increase of surface area,

(2) an increase of temperature,

(3) a decrease in humidity,

(4) an increase in wind speed.

Question 18. The melting point of ice is 273.16 K. What does this mean? Explain in detail.

Answer: Ice is solid at 0°C i.e., 273° K. The molecules of ice are tightly packed. These molecules have to overcome the force of attraction with which they are held

and hence they gain this heat from the surrounding but the temperature remains the same as their energy is used to overcome the force of attraction between the particles. The particles have their state and start vibrating freely and a stage reaches when the solid ice melts and is converted to liquid state at the same temperature i.e., 273 K.

Question 19. How is the high compressibility property of gas useful to us?

Answer: The gasses have high compressibility. This property is used in the following situation:

(1) LPG (liquefied petroleum gas) is a fuel which is made up of petroleum gas. On compressing this petroleum gas it forms liquid.

(2) Oxygen cylinders in the hospitals have compressed gas filled in them.

(3) CNG (compressed natural gas) is a natural gas, methane, which is compressed and used as a fuel in vehicles and at home.

Question 20. With the help of an example, explain how diffusion of gasses in water is essential?

Answer: The gasses from the atmosphere diffuse and dissolve in water. Gasses like oxygen and carbon dioxide diffuse in water, are essential for the survival of aquatic animals and plants.

Animals breathe in this oxygen dissolved in water for their survival and plants can use carbon dioxide dissolved in water for photosynthesis.

In Our Surrounding class 9 CHEMISTRY long question:

Question 1. Pressure and temperature determine the state of a substance. Explain this in detail.

Answer: (1) Any matter i.e., solid, liquid or gas when it experiences an increase in temperature then it changes its state.

Take ice cubes in a beaker or heat them slowly, the temperature increases and the ice melts to form liquid. Heat this liquid further and it will become steam.

(2) On lowering down the temperature of any matter, show change in their state.

Take the steam that is coming out of the boiling water and allow it to cool down, it condenses to form water and on further cooling of this water we get ice.

(3) On applying pressure and reducing temperature we can liquefy gasses or change them into solid.

Example: Take carbon-dioxide gas, reduce its temperature and apply a lot of pressure on it so that it changes into solid carbon dioxide, called diy ice, which is used as a refrigerant for cooling.

If the pressure on it is decreased it directly changes into gas.

In LPG cylinders, the petroleum gas is cooled and with a lot of pressure changes it into a liquid state.

While using this LPG, we release the pressure exerted on it and hence it comes out in the form of gas.

Question 2. Explain by giving examples the various factors on which the rate of evaporation depends.

Answer: The rate of evaporation depends on the following factors:

(1) Surface area: If the surface area is increased the rate of evaporation also increases.

(a) To dry the clothes we spread them to dry faster.

(b) Tea in a saucer cools faster than in a cup.

(2) Temperature: If the temperature is increased the rate of evaporation also increases. Due to an increase in temperature the particles gain more kinetic energy and change their phase from liquid to gaseous. Water will evaporate faster in the sun than in the shade.

(3) Humidity: It is the amount of water vapor present in air. The air can hold a definite amount of water vapor, at a given temperature. If the amount of water vapor is high in the air then the rate of evaporation decreases. On hot and humid days, desert coolers are not effective as the air cannot hold any more moisture to get the cooling effect.

(4) Wind speed: With the increase in wind speed, the rate of evaporation increases. The particles of water vapor move away with the wind, decreasing the amount of water vapor in the surrounding area.