Kerala SSLC Class 9 Solutions for Physical Sciences – Nature of Materials

Kerala SSLC Class 9 Solutions for  Physical Sciences – Nature of Materials (English Medium)  Part-1

Exercise 7:

Question 1:

• What are the different physical states of the articles?
• Which among them are the materials in solid state?
• Which are the materials in other state?

Solution:

• The different physical states of the articles are solid, liquid and gaseous.
• Various kinds of utensil, bucket, gas stove, vegetable, almirah, pipe, gas cylinder are the materials in solid state.
• Tap water and water in the utensil are in the liquid state.
• Cooking gas (LPG) and vapour are in the gaseous state.

Question 2:

Observe the materials in different states of matter and fill up the table given below. (✓ whatever is applicable)

	Solid	Liquid	Gas
Has fixed volume
Has fixed shape

Solution:

	Solid	Liquid	Gas
Has fixed volume	✓	✓
Has fixed shape	✓

Question 3:

Why do solid substances have a permanent shape? Why is it that there is no permanent shape for liquids? Does the molecular arrangement play any part in this?

Solution:

• In solids, the space between the particles is very less and the force of attraction between these particles is strong. Thus, particles in a solid are closely packed.
• The kinetic energy of the particles is very less and so solids have an orderly arrangement of the particles. Therefore, solids have a definite shape and a fixed volume.
• Solids maintain their shape even when they are subjected to external force i.e. they are rigid.
• In liquids, the space between the particles is slightly more as compared to the solids, but still very less as compared to the gases.
• The particles of liquid can slip and slide over each other.
• The force of attraction between the particles is strong enough to hold the particles together but not strong enough to hold the particles in a fixed position.
• Thus, the particles in a liquid are not as closely packed as in solids.
• The kinetic energy of the liquid particles is more than that of the solids. Thus, they have a disorderly arrangement of particles compared to solids.
• Liquids do not have a fixed shape but have a fixed volume and they take up the shape of the container in which they are poured in.

Higher Education Scholarship

Question 4:

Fill a glass tumbler with water. Using an ink filler, carefully pour a little ink on the water surface.

• What do you observe?
• What is the reason? Think in terms of molecular motion in liquids.
• Does ink spread into the wall of the glass vessel as it does in water? Why?

1. What do you observe?
2. What is the reason? Think in terms of molecular motion in liquids.
3. Does ink spread into the wall of the glass vessel as it does in water? Why?

Is it due to the fact that the molecules of glass are closer to one another than the molecules of water? Arrive at a conclusion by comparing the molecular motion in solids and liquids.

Solution:

• Observation:
  Since water is in liquid state, the molecules of water move from one place to another. So there are empty spaces between them and the particles of ink get into the space between the particles of water. The ink thus diffuses into the water.

• Inference:
  Molecules in water (or in any other liquid) are always in continuous motion.

• The ink does not spread into the wall of the glass vessel as it is in the solid state and the particles are closely packed.

As water exist in liquid state; the molecules have more freedom of movement and the distance between the two molecules is more.
As glass exists in solid state, the molecules can vibrate only in their fixed positions. Therefore, the distance between the molecules and the freedom of movement between them is negligible.
Conclusion:
In solids, the molecules are closely packed but in liquids, the molecules are far apart and can slip and slide over each other. Unlike in liquids, the molecules in the solids have no freedom of movement. The particles of solids can vibrate only about its mean position.

Aikyashree Scholarship

Exercise 8:

Question 1:

Solids can be converted to liquids. How is this done? What properties of solids change when such a conversion happens? Among the statements ‘✓’ which are suitable.
□Loses permanent shape.
□Molecules begin to move faster.
□Molecules are free to move in any direction.
□Molecular motion is reduced.

Solution:

✓ Loses permanent shape.
✓ Molecules begin to move faster.
□ Molecules are free to move in any direction.
□ Molecular motion is reduced.

Question 2:

Tabulate the changes in molecular arrangement when a solid becomes liquid and when a liquid becomes gas.

	When a solid becomes liquid	When a liquid becomes gas
Movement of molecules
Distance between molecules
Attraction between molecules

Solution:

	When a solid becomes liquid	When a liquid becomes gas
Movement of molecules	Increases	Increases
Distance between molecules	Increases	Increases
Attraction between molecules	Decreases	Decreases

 

Question 3:

When substances are heated, does the energy of the molecules increase? Or does it decrease?
What about the effect of cooling?

Solution:

• Physical state of the substances changes when heat is absorbed or given out.
• When substances are heated, the energy of the molecules increases. For example, when a solid substance is heated, the kinetic energy of the molecules increases.
• When solid substances are cooled, the kinetic energy and the freedom of movement of molecules decreases.

Question 4:

Write down the change in the energy of molecules in the case of changes listed below.

Solution:

Question 5:

In a glass tumbler filled with water, we can introduce a spoon and stir it easily. If the same water is put in a freezer and turned to ice, can it be stirred?
What could be the reason?

Solution:

When water changes its state from liquid to solid, the distance between the molecules decreases. The molecules come closer to each other and it gains a definite shape. Hence, we can’t stir the ice kept in a freezer by using a spoon.

Question 6:

An ice cube has firm surfaces.
What about the nature of the surface when this ice cube melts and turns into water?
Like water, every liquid has a surface.
How is this surface formed?

Solution:

An ice cube has firm surfaces.
When this ice cube melts and turns into water, the surface tension of the liquid increases.
The molecule at the surface experiences attraction mainly from either side or downward. This is one reason why water and other liquids have a surface.

The molecules inside the water attract the molecules on the surface and pull it down with great force. Thus, a surface is formed.

Question 7:

Observe the arrangement of molecules in solid, liquid and gas,

Prepare a note on the peculiarities of the distribution of molecules as well as the distance between molecules in the three different states of substances. Enter it in the science diary.

Solution:

Solids:

• In solids, the space between the particles is very less.
• The force of attraction between the particles is strong. Thus, they are closely packed.
• The kinetic energy of the particles is very less and so solids have an orderly arrangement of the particles. Therefore, solids have a fixed shape and a fixed volume.
• They maintain their shape even when they are subjected to external force i.e. they are rigid.

Liquids:

• In liquids, the space between the particles is slightly more as compared to the solids, but still very less as compared to the gases. The particles of liquid can slip and slide over each other.
• The force of attraction between the particles is strong enough to hold the particles together but not strong enough to hold the particles in a fixed position.
• Thus, the particles in a liquid are not as closely packed as in solids.
• The kinetic energy of the particles is more than that of the solids. Thus, liquids have a disorderly arrangement of particles compared to solids.
• Liquids do not have a fixed shape but have a fixed volume. Liquids take up the shape of the container in which they are poured in.

Gases:

• In gases, the particles are farther apart from one another as compared to the solids and liquids. They have a very disorderly arrangement of particles compared to the solids and liquids.
• The force of attraction between the particles is negligible, hence particles of a gas move freely in all the directions. Gases thus can mix or diffuse into other gases.
• The particles of a gas have maximum kinetic energy. They move with high speed in all directions and can exert pressure on the walls of its container.
• Gases neither have a definite shape nor a definite volume. They fill up the container completely.
• Gases can be compressed easily. Example: the LPG cylinders used at home and the CNG cylinders used in vehicles.

Exercise 9:

Question 1:

Observe the illustration of the molecules in a jar of water. The attraction of some molecules by the surrounding molecules is shown.

• Is there any difference in the force of attraction exerted by other molecules on those at the surface and those in the interior?
• Does this surface have any peculiarity?

Solution:

• The molecule at the surface experiences attraction mainly from either side or downward. This is one reason why water and other liquids have a surface.
• Since it has surface tension it can serve as a plane surface. The movement of small creatures along the surface of water and the retention of a blade on the water surface without sinking are examples of this peculiarity.

Question 2:

Take a glass and fill it with water.
Drop small coins or needles into the water. How many coins can you put in without the water overflowing?

Solution:

In a standard size glass, we can put approximately twelve to fifteen coins to it. The middle portion of the surface of water rises and forms a curved surface. This is due to the surface tension.

Question 3:

Place a razor blade carefully on the surface of water. What do you observe?

Solution:

We will observe that the blade floats on the water.

Exercise 10:

Question 1:

Observe the water surface around the blade. Does the water surface function like a stretched film? Can you explain with reference to the illustration of the molecules on the surface of a liquid?

Solution:

The resultant force experienced on a molecule on the liquid surface is not zero. It acts downwards and as a result of it the liquid surface will act as a stretched membrane. This has a tendency to reduce its surface area. Thus, the molecules at the surface attract each other with a force thus creating surface tension.

Question 2:

Solids which are denser than liquids generally sink into those liquids. But what happens if the shape of the solid is altered so that it could displace the liquid equal to its own weight? Then the solid floats on the liquid. This is how ships and other things made from iron float on water. But what about pins and blades?

Solution:

The pins and blades will also float on water.

Question 3:

How do you explain the observation that a pin, blade or paper clip can float on the surface of water? Explain this in relation to surface tension.

Solution:

• Pin, blade and paper clip would float on water if they are placed very carefully and horizontally so that the surface area becomes the maximum.
• The force which causes this phenomenon is called surface tension and is due to the surface tension that certain objects float in water.
• The surface of the liquid acts as a stretched membrane because the molecules on the surface experience force only to the sides and into the inner side of the liquid.
• If any object displaces water equal to its weight it will float in water. If the substances denser than the liquid are converted into such a shape that it can displace the liquid equal to its weight; it will float in the liquid.

Consolidation

• The surface of a liquid acts as a stretched membrane due to surface tension.
• It is due to the surface tension that a blade or a pin floats on water if it is placed very carefully.

Question 4:

Dissolve sufficient quantity of soap in water and place a blade on the surface.
Why does the blade sink?

Solution:

When the sufficient quantity of soap is dissolved in water, the surface tension decreases. Hence, the blade sinks in water.

Question 5:

Does surface tension have any relevance on the use of soap for washing clothes?

Solution:

• When the sufficient quantity of soap is dissolved in water, the surface tension decreases.
• When soap dissolves in water their comparatively large molecules come in between the water molecules and as a result the water molecules move apart and hence the force of attraction decreases.
• This reduces the surface tension. That is why the surface tension decreases when soap is added.
• The soap water gets deep into the holes of the cloth and removes the stains easily.
• As the polar end of soap molecules come in contact with water molecules the distance between the water molecules increase and hydrogen bonding decreases. Also because of this the surface tension may decrease.

Question 6:

Some experiments can be carried out by making a thin film of water.
Connect two thin copper wires with cotton threads and allow them to hang as shown in the figure.

• What do you observe?
• Why do the threads come closer and reduce the surface area of the film? What is the force that brings the threads closer?

Solution:

• Threads come closer and decrease the surface tension of a soap film.
• Soap film reduces the surface tension, hence the surface area decreases. Adhesive force will bring the threads closer.

Exercise 11:

Question 1:

Take a metal ring or a thin plastic bangle and tie a cotton thread loosely across the ring away from the centre, as shown in the figure. Dip the ring or bangle in soap water and raise it slowly.

• Haven’t you obtained a circular soap film inside it?

Now using the point of a pencil break the larger portion of the film between the ring and the thread.

• What do you observe?

Dip the ring in soap water and make a soap film again. Now break the smaller portion of the soap film.

• What is observed now?
• Draw in the figure your observation showing to which side the thread is pulled?

• Does surface tension force the surface to shrink or expand?
• Does the surface area of a liquid decrease or increase as a result of surface tension?

Solution:

• Yes. We will be able to see a circular soap film inside the ring.
• Observation: Soap film between the bangle and thread, breaks and a new surface is formed. That is, the soap film exists in the smaller area and the thread gets stretched into that part.
• Observation: By breaking the smaller portion of the soap film, the soap film exists in the larger area and the thread gets stretched into that part.
• The thread stretched to the larger area.

• Surface tension tends to shrink the surface.
• Surface area will decrease.

Exercise 12:

Question 1:

Put a small drop of mercury on a glass plate (handle mercury with care as it is harmful to the body). Next to it put two drops together. Close to this put a few drops together.

• What is the difference that you observe in the shape of the drops?
• How does the weight affect the spreading of drops? What about small drops?
• Blow carefully on one of the drops so as to bring it closer to the next. Don’t you see the two drops merging into a single drop? Why does this happen?
• Is not cohesion the force responsible for surface tension also? Discuss.

Solution:

• Small droplets get spherical shape on account of surface tension. The bigger droplets get flattened from the middle but have round shape near the edges.
• The centre of gravity of the bigger droplets is lowered due to its heavy weight. As a result, the bigger droplets get flattened from the middle. Small droplets take spherical shape due to surface tension.
• Due to the attractive force between the similar molecules. Water droplets will also combine when brought together. The force of attraction between molecules of same substance is termed, cohesion.
• Yes, cohesion force is the cause of surface tension.

Question 2:

If the glass surface is tilted, do the mercury drops start rolling? What would be the result if water drops are put on the glass plate?

Solution:

Observation:
We can see that mercury drop roll down along the glass surface, whereas the drops of water can join together to form a spherical shape.
It is the force of attraction between molecules of glass and molecules of water that causes water drops to stick to glass. This kind of force of attraction between molecules of one substance and molecules of another substance is called adhesion.

Question 3:

Take a glass slide and dip it in a beaker of water so that half the slide is immersed. Take out the glass slide, wipe it and dip it in a similar manner in mercury.

• In the figure write the names of the liquids, based on your observation.
• In which circumstance does the liquid’s force of cohesion exceed the force of adhesion with the glass surface?

Solution:

• Names of the liquid in the given figure.

• Cohesive force is greater than that of adhesive force when glass slide is dipped in mercury.
  Reason for this is-If the cohesive force between the molecules of the liquid is less than the adhesive force of glass slide and liquid, meniscus will be concave. If the cohesive force is greater than the adhesive force, the meniscus will be convex.

Exercise 13:

Question 1:

Some situations are given below.

• Water is poured on a taro (colocasia) leaf.
• Wind screen of a motor car gets wet in the rain.
• An oil smeared vessel is dipped in water.
• Mercury is poured on a glass plate.
• Wax paper is dipped in water.
• Rain drops fall on a new umbrella.
• A person gets wet in the rain.

Analyse these situations and fill up the table suitably.

Cohesion more Adhesion less	Cohesion less Adhesion more

Solution:

Cohesion more Adhesion less	Cohesion less Adhesion more
Water is poured on a taro (colocasia) leaf. An oil smeared vessel is dipped in water. Mercury is poured on a glass plate. Rain drops fall on a new umbrella. Wax paper is dipped in water.	Wind screen of a motor car gets wet in the rain. A person gets wet in the rain.

Question 2:

Have you noticed thin tubes (capillary tubes) attached to the nibs of certain fountain pens? With such pens you can write even on a paper pasted to a wall, with the nib held upward. How does the ink .move upward in such pens? Should not the ink flow downward because of its weight?

Solution:
This is due to capillarity, i.e. ink rises up against the force of gravity.

Exercise 14:

Question 1:

Are there other situations where a liquid flows upward, against gravitational attraction?

Solution:

• Water rises up through cracks in the plastering of walls.
• Water rises up through capillary tubes.
• When one end of the chalk or sponge is dipped in water, water rises up along with it.

Question 2:

Take two clean and dry glass slides.
Place them together and lower them into a vessel containing water mixed with a little ink.
Does the water move upward between the slides?

Solution:
Yes, water rises up in between the slides.
Question 3:

Take coloured water in a beaker. Dip a glass capillary tube into the water.
Note your observations.

• What could be the reason for this?
• Doesn’t the water inside the tube have weight?
• What is the force which keeps the water raised?
• If the liquid inside the tube is heavier, will it rise to the same height?

Solution:

• Water rises up through the glass tube due to capillarity.
• Yes. The water inside the tube has weight.
• Capillary force keeps the water raised in the glass tube.
• No. Capillary force is the force against the force of gravity. Liquids having more weight experience more force of gravity. So the capillarity will decrease.

Question 4:

Dip glass tubes of different diameters in water and examine the capillary rise.
When the internal diameter of the tube increases, does the weight of water entering the tube increase or decrease?

• Among the illustrations given in the figure, which are the ones justifying your observation?
• When the diameter of the tube increases capillary rise……………………
• What could be the reason?

………………………………..

Exercise 15:

Question 1:

See the chalk lamp experiment demonstrated in a science exhibition

• How could the small holes inside the chalk have helped the kerosene to move upward?
• Is this the same as what happens inside an ordinary kerosene lamp (wick lamp)?
• Would this also be the reason for cotton cloth getting soaked in water?

Solution:

• Small holes in the chalk serve as capillary tubes.
• Wick in the kerosene lamp acts as a capillary tube.
• Yes. The tiny holes in the cotton clothes act like a capillary tube having small diameter.

Question 2:

What are the other situations where we utilise capillary rise?

Solution:

Situations where we utilise capillary rise are-

• Absorption of water using sponge.
• Rising of cold drink through straw while drinking.
• Towel is used to wipe sweat. The sweat gets absorbed in the towel through capillary action.
• Sprinkle water on a brick. Brick absorbs water through capillary action.
• Absorption of water using cotton clothes through capillary action.
• Blotting of ink using blotting paper has capillary action.

Question 3:

Spill some ink on a desk. Blot it with a piece of chalk. Do the same with a blotting paper?

Solution:
Ink spilt on the desk is absorbed by a chalk piece. Similarly, blotting paper also absorbs ink. This is due to the capillarity.

Question 4:

Take a dry clod of earth and divide it into two pieces. Break up one piece into small grains and the other piece into fine powder and fill them in two separate glass tubes. Close one end of each tube with cotton cloth. Pour water up to a height of three or four centimetres in a trough and lower the cloth covered ends of the tubes into it.
Observe after some time.

• In which tube did the water rise to a greater height?
• In which tube are the capillaries formed in the soil smaller in diameter?
• How do you relate this to the hoeing of the soil before summer begins? Find out by analysing the experiments you have carried out.