Class 8 | Science | Complete Questions with Answers
Chapter 7: Particulate Nature of Matter
Section A: Multiple Choice Questions
(1 Mark Each)
1. The basic unit that makes up a larger piece of a
substance or material is called a:
(a) Molecule (b) Constituent particle (c) Compound (d)
Mixture
Answer: (b) Constituent particle
2. Grinding a stick of chalk into fine powder is an
example of:
(a) A chemical change (b) A physical change (c) A nuclear
change (d) None of these
Answer: (b) A physical change
3. When sugar dissolves in water, it breaks up into its:
(a) Vapour (b) Constituent particles (c) Gas bubbles (d)
Solid crystals
Answer: (b) Constituent particles
4. The empty spaces between the particles of matter are
called:
(a) Voids (b) Interparticle spaces (c) Vacuum pockets (d)
Molecular gaps
Answer: (b) Interparticle spaces
5. The attractive forces that hold the constituent
particles of matter together are called:
(a) Gravitational forces (b) Interparticle attractions (c)
Magnetic forces (d) Frictional forces
Answer: (b) Interparticle attractions
6. In which state of matter is the interparticle
attraction the strongest?
(a) Solid (b) Liquid (c) Gas (d) All are equal
Answer: (a) Solid
7. In which state of matter is the interparticle
attraction negligible?
(a) Solid (b) Liquid (c) Gas (d) None
Answer: (c) Gas
8. In solids, the constituent particles can only:
(a) Move freely from place to place (b) Vibrate about their
fixed positions (c) Flow like liquids (d) Diffuse rapidly
Answer: (b) Vibrate about their fixed positions
9. The minimum temperature at which a solid melts into a
liquid at atmospheric pressure is called its:
(a) Boiling point (b) Freezing point (c) Melting point (d)
Condensation point
Answer: (c) Melting point
10. The temperature at which a liquid boils and turns
into vapour at atmospheric pressure is called its:
(a) Melting point (b) Boiling point (c) Sublimation point (d)
Freezing point
Answer: (b) Boiling point
11. As per Table 7.1 in the chapter, which of the
following has the highest melting point?
(a) Ice (b) Urea (c) Iron (d) Wax
Answer: (c) Iron
12. Liquids generally have:
(a) Fixed shape and fixed volume (b) No fixed shape but
fixed volume (c) No fixed shape and no fixed volume (d) Fixed shape but no
fixed volume
Answer: (b) No fixed shape but fixed volume
13. Gases have:
(a) Fixed shape and volume (b) No fixed shape but fixed
volume (c) No fixed shape and no fixed volume (d) Fixed shape only
Answer: (c) No fixed shape and no fixed volume
14. Liquids and gases, since both flow and have no fixed
shape, are together classified as:
(a) Solids (b) Fluids (c) Plasmas (d) Compounds
Answer: (b) Fluids
15. The ancient Indian philosopher who first proposed the
idea of 'Parmanu' was:
(a) Aryabhata (b) Acharya Kanad (c) Charaka (d) Sushruta
Answer: (b) Acharya Kanad
16. Acharya Kanad's idea of the Parmanu was written in
his work called:
(a) Arthashastra (b) Charaka Samhita (c) Vaisheshika Sutras
(d) Sushruta Samhita
Answer: (c) Vaisheshika Sutras
17. The slow process by which a liquid changes into
vapour only at its surface, even below the boiling point, is called:
(a) Boiling (b) Evaporation (c) Condensation (d) Sublimation
Answer: (b) Evaporation
18. Suspended Particulate Matter (SPM), a term used in
the context of air pollution, refers to:
(a) Constituent particles of matter (b) Tiny dust particles
suspended in air (c) Molecules of oxygen (d) Water vapour particles
Answer: (b) Tiny dust particles suspended in air
19. In the activity with potassium permanganate, the pink
colour spreads the fastest in:
(a) Ice-cold water (b) Water at room temperature (c) Hot
water (d) It spreads at the same rate in all
Answer: (c) Hot water
20. The spreading of smoke from one gas jar into another
when placed together demonstrates that gas particles:
(a) Are completely stationary (b) Move freely and constantly
in all directions (c) Have very strong interparticle attraction (d) Have a
fixed volume
Answer: (b) Move freely and constantly in all directions
21. Which of the following is practically incompressible?
(a) Air (b) Water (c) Smoke (d) Iodine vapour
Answer: (b) Water
22. When the plunger of an air-filled syringe (with the open
end blocked) is pushed inward, the volume of air:
(a) Increases (b) Decreases (c) Remains the same (d) Becomes
zero
Answer: (b) Decreases
23. In liquids, the constituent particles are:
(a) Tightly packed with no movement at all (b) Free to move,
but only within a limited space (c) Completely free with negligible attraction
(d) Fixed in one position permanently
Answer: (b) Free to move, but only within a limited space
24. The ability to flow is a property shared by:
(a) Solids only (b) Liquids and gases (c) Solids and liquids
(d) None of these
Answer: (b) Liquids and gases
25. When water is heated to its boiling point, bubble
formation occurs:
(a) Only at the surface (b) Only at the bottom of the vessel
(c) Both at the surface and within the liquid (d) Nowhere in the liquid
Answer: (c) Both at the surface and within the liquid
26. Ice is an exception among solids because its
particles are:
(a) Closer together than in liquid water (b) Farther apart
than in liquid water (c) At the same distance apart as in water (d) Arranged
randomly, unlike other solids
Answer: (b) Farther apart than in liquid water
27. A molecule of water is made up of:
(a) One hydrogen atom and one oxygen atom (b) Two hydrogen
atoms and one oxygen atom (c) Two hydrogen atoms and two oxygen atoms (d) One
hydrogen atom and two oxygen atoms
Answer: (b) Two hydrogen atoms and one oxygen atom
28. Two atoms of hydrogen combine with each other to
form:
(a) A compound (b) A molecule of hydrogen (c) An ion (d) A
mixture
Answer: (b) A molecule of hydrogen
29. While washing oil-stained clothes with soap, one end
of the soap particle attaches to the:
(a) Water (b) Oil (c) Fabric (d) Air
Answer: (b) Oil
30. The interparticle spacing is maximum in which state
of matter?
(a) Solid (b) Liquid (c) Gas (d) All states have equal
spacing
Answer: (c) Gas
Section B: Short Answer Questions (2
Marks Each)
1. What is a constituent particle? Give one example.
A constituent particle is the basic unit that makes up a
larger piece of a substance or material.
Example: the tiny grains obtained on grinding chalk to the
point where they cannot be broken down further are the constituent particles of
chalk.
2. Is grinding chalk into powder a physical change or a
chemical change? Justify your answer.
It is a physical change. The chalk does not change into a
new substance on grinding; only the size of each speck of chalk is reduced
further, while it remains chalk.
3. What are interparticle spaces? Name one activity from
the chapter that demonstrates them.
Interparticle spaces are the empty spaces between the
constituent particles of matter. Activity 7.7 (dissolving sugar in water and
comparing water levels) demonstrates that such spaces exist, since the final
volume of the solution is less than the sum of the separate volumes of water
and sugar.
4. What are interparticle attractions? On what two
factors does their strength depend?
Interparticle attractions are the attractive forces that
hold the constituent particles of matter together. Their strength depends on
the nature of the substance and the interparticle distance.
5. Define melting point. What is the melting point of
ice?
Melting point is the minimum temperature at which a solid
changes into a liquid at atmospheric pressure. The melting point of ice is 0°C.
6. Define boiling point. How is it different from
evaporation?
Boiling point is the temperature at which a liquid boils and
turns into vapour at atmospheric pressure. Boiling occurs at this fixed
temperature and takes place throughout the liquid; evaporation, on the other hand,
is a slower process that occurs only at the surface of the liquid, at any
temperature.
7. Why do solids have a definite shape and a definite
volume?
In solids, the constituent particles are tightly packed and
held together by very strong interparticle attractions, which keep them fixed
in position (only vibration is possible). This gives solids a definite shape
and volume.
8. Why do liquids have no fixed shape but a fixed volume?
In liquids, the interparticle attraction is slightly weaker
than in solids, so particles can move within a limited space and take the shape
of their container. However, they remain close enough together that the total
volume stays fixed.
9. Why do gases have neither a fixed shape nor a fixed
volume?
In gases, the interparticle attraction is negligible, so
particles are free to move in all directions and spread out to fill the entire
available space, giving gases neither a fixed shape nor a fixed volume.
10. What idea did Acharya Kanad propose about the nature
of matter, and in which work is it recorded?
Acharya Kanad proposed that matter is made up of tiny,
indivisible, eternal particles called Parmanu (atom). This idea is recorded in
his work called the Vaisheshika Sutras.
11. What is Suspended Particulate Matter (SPM)? How is it
different from the constituent particles of matter?
SPM refers to the tiny dust particles suspended in air. It
is different from the constituent particles of matter, which are extremely
small compared to dust particles — in fact, even dust particles are made up of
a very large number of constituent particles (atoms and molecules).
12. Why is water practically incompressible, while air
can be compressed easily?
Water particles are already closely packed with very little
interparticle space between them, so they cannot be pushed much closer
together. Air particles have large interparticle spaces, so they can be brought
closer together under pressure, making air compressible.
13. Why does sugar dissolve completely in water, while
sand does not?
Water particles are able to pull apart the constituent
particles of sugar and these particles occupy the interparticle spaces of
water, so sugar dissolves. In sand, the constituent particles are held together
by very strong interparticle attraction that water particles cannot overcome,
so sand does not dissolve.
14. Why does the water level first rise and then decrease
slightly when sugar is dissolved in it?
The water level rises when solid sugar is added because it
occupies additional space. After the sugar dissolves, its constituent particles
occupy the interparticle spaces between water particles rather than adding
fully to the volume, so the level decreases slightly compared to the risen
level.
15. Why does potassium permanganate spread faster in hot
water than in cold water?
Heating increases the thermal energy of water particles,
making them move faster. These faster-moving particles pull out and spread the
potassium permanganate particles more quickly, so the colour spreads faster in
hot water.
16. Using the incense-stick activity, explain how the
movement of gas particles can be
demonstrated.
When an incense stick is lit in one corner of a room, the
fragrance is felt near the stick at first but soon spreads throughout the room.
This happens because air particles are constantly moving and hit the fragrance
particles, carrying them throughout the room — showing that gas particles are
in continuous, free motion.
17. What are fluids? Name the two states of matter
classified as fluids, giving a reason.
Fluids are substances that flow and do not have a fixed
shape. Liquids and gases are classified as fluids because both flow and take
the shape of the container they are kept in.
18. Why can you move your finger freely through water but
not through a solid block of the same size?
In liquids, the interparticle attraction is not strong
enough to keep the particles rigidly fixed, so they can be temporarily
displaced by a finger and then flow back into position. In solids, strong
interparticle attraction holds particles firmly in fixed positions, so they
cannot be displaced this way.
19. What happens to the interparticle attraction and
interparticle spacing when a solid changes into a liquid?
When a solid changes into a liquid, the interparticle
attraction weakens and the interparticle spacing increases slightly, allowing
the particles to move out of their fixed positions within a limited space.
20. How does soap help in removing oil stains from
clothes?
Soap particles surround the oil particles on the fabric —
one end of a soap particle attaches to the oil, while the other end mixes with
water, helping lift the oil off the fabric and wash it away.
Section C: Three-Mark Questions
1. Describe the activity performed with a stick of chalk
(Activity 7.1) to show that matter is composed of extremely small particles.
What conclusion is drawn from it?
• A chalk stick is broken into two pieces, then broken
repeatedly until it becomes difficult to break further by hand.
• The small pieces are ground into a fine powder using a
mortar and pestle, and observed under a magnifying glass.
• Each tiny grain observed is still a speck of chalk (same
substance) — this shows that chalk is made up of a large number of extremely
small constituent particles, and grinding is only a physical change.
2. Explain, with reference to Activity 7.2 (dissolving
sugar in water), how the presence of sugar in water can be confirmed even
though sugar particles cannot be seen.
• Two teaspoons of sugar are added to water without
stirring; the top layer does not taste sweet initially.
• After stirring until the sugar dissolves completely, the
top layer of water tastes sweet, even though no sugar particles can be seen.
• This confirms sugar is present in the solution — it has
broken into constituent particles that are too small to see but can be sensed
by taste, and these particles spread throughout the water.
3. Describe the syringe activity (Activity 7.6) and
explain what it shows about the interparticle spacing in gases as compared to
liquids.
• Air is trapped in a syringe (needle removed) by blocking
the open end with a thumb, and the plunger is pushed inward.
• The volume of air decreases easily, showing that gas
particles have large interparticle spaces that can be reduced under pressure.
• When the activity is repeated with water instead of air,
the water is found to be practically incompressible, showing that liquid
particles have very little interparticle space between them.
4. Explain, with reasoning, why solids have a definite
shape and volume, while liquids and gases do not have a definite shape.
• In solids, particles are tightly packed and interparticle
attraction is very strong, holding particles in fixed positions (only vibration
is possible) — giving a definite shape and volume.
• In liquids, interparticle attraction is slightly weaker,
so particles can move within a limited space and take the shape of their
container, though the volume stays fixed.
• In gases, interparticle attraction is negligible, so
particles move freely in all directions and spread to fill all available space
— giving neither a fixed shape nor a fixed volume.
5. Describe the activity performed using two gas jars and
incense-stick smoke (Activity 7.5), and explain what it demonstrates about the
properties of gases.
• Smoke from a burning incense stick is trapped in Gas Jar A
(held upside down), which is then covered with a glass plate; Gas Jar B is
placed upside down over the glass plate.
• When the glass plate is carefully removed, the smoke is
observed to spread from Gas Jar A into Gas Jar B, filling the entire available
space.
• This shows that gases do not have a fixed volume and that
gas particles move freely and constantly in all directions, with negligible
interparticle attraction.
6. Explain the relationship between the thermal energy of
particles, interparticle distance, and the physical state of a substance.
• Thermal energy is the heat energy possessed by the
particles of a substance; higher temperature means higher thermal energy.
• As thermal energy increases, particles vibrate/move more
vigorously, which increases the interparticle distance and weakens the
interparticle attraction.
• It is this balance between thermal energy and
interparticle attraction that ultimately decides whether a substance exists as
a solid, liquid, or gas at a given temperature.
7. Explain, using the example of ice, water, and steam,
how interparticle attraction and spacing change during melting and boiling.
• In ice (solid), particles are closely packed with strong
interparticle attraction and minimum spacing, only vibrating about fixed
positions.
• At the melting point (0°C), thermal energy overcomes some
of the attraction; particles move out of fixed positions, spacing increases
slightly, and ice changes into water (liquid).
• At the boiling point (100°C), particles gain enough
thermal energy to overcome interparticle attraction almost completely; spacing
becomes maximum and attraction becomes negligible as water changes into steam
(gas).
8. Describe the activity of dissolving potassium
permanganate in water (Activity 7.8) and explain why the pink colour spreads
throughout the water.
• A few grains of potassium permanganate are dropped into a
glass tumbler of water without stirring.
• Initially, streaks of pink colour spread out from the
grain; with time, the entire water becomes uniformly pink.
• This happens because water particles are in constant
motion — they pull out particles of potassium permanganate from the grain and
then hit these particles, spreading them throughout the liquid.
9. Differentiate between boiling and evaporation, giving
at least three points of difference.
• Boiling occurs at a fixed temperature (the boiling point);
evaporation can occur at any temperature.
• Boiling takes place throughout the liquid, with bubble
formation both at the surface and within the liquid; evaporation occurs only at
the surface of the liquid.
• Boiling is a fast process; evaporation is a slow process.
10. Explain the contribution of Acharya Kanad to the
concept of the particulate nature of matter.
• Acharya Kanad was an ancient Indian philosopher who, long
before modern atomic theory, proposed that matter is made up of tiny,
indivisible, eternal particles.
• He called these particles Parmanu (atom).
• This idea was recorded in his work called the Vaisheshika
Sutras, reflecting India's early scientific heritage in thinking about the
nature and structure of matter.
Section D: Long Answer Questions (5
Marks Each)
1. Describe, with suitable activities, how it can be
shown that matter is made up of extremely small particles. Explain the concept
of a 'constituent particle' with reference to chalk and sugar.
• Activity 7.1 (chalk) — a chalk stick is broken repeatedly
and ground into a fine powder using a mortar and pestle; observed under a
magnifying glass, each tiny speck is still chalk.
• If grinding could continue indefinitely, a stage would be
reached where the particles cannot be broken down any further — these are the
constituent particles, the basic building blocks of chalk.
• Activity 7.2 (sugar) — sugar dissolved in water cannot be
seen, but its presence is confirmed by taste; sugar breaks into constituent
particles that are too small to see.
• Both activities show matter is composed of a very large
number of extremely small particles that cannot be seen even under an ordinary
microscope.
• A constituent particle is thus the basic unit that makes
up a larger piece of any substance or material.
2. Explain, in detail, the arrangement, interparticle
attraction, and movement of particles in solids, liquids, and gases. Support
your answer with a suitable comparison.
• Solids — particles are closely/tightly packed;
interparticle attraction is maximum; movement is restricted to vibration about
fixed positions; interparticle spacing is minimum; solids have a definite shape
and volume.
• Liquids — particles are a little more loosely packed than
in solids; interparticle attraction is slightly weaker than in solids;
particles can move, but only within a limited space; interparticle spacing is a
little more than in solids; liquids have a fixed volume but no fixed shape.
• Gases — particles are free to move in all directions;
interparticle attraction is minimum/negligible; interparticle spacing is
maximum; gases have neither a fixed shape nor a fixed volume.
• This progression from solid to liquid to gas shows a
steady decrease in interparticle attraction and a steady increase in
interparticle spacing and freedom of movement.
• Everyday examples: iron nail (solid), water (liquid), and
air or steam (gas) illustrate this progression.
3. Describe the syringe activity and the activity of
pouring water into containers of different shapes, and explain what each
demonstrates about the properties of gases and liquids respectively.
• Syringe activity (7.6) — air trapped in a syringe (needle
removed, open end blocked) compresses easily when the plunger is pushed inward,
showing gas particles have large interparticle spaces that can be reduced under
pressure.
• Repeating the syringe activity with water shows that water
is practically incompressible, since liquid particles are already closely
packed with minimal space between them.
• Water-in-containers activity (7.4) — water filled to a 200
mL mark in Container A is transferred to differently shaped Containers B and C;
the water takes the shape of each new container.
• However, the water level remains at 200 mL in every
container, showing that liquids have no fixed shape but do have a fixed
(definite) volume.
• Together, these activities show that gases are
compressible and have neither fixed shape nor fixed volume, while liquids are
(practically) incompressible, take the shape of their container, but keep a fixed
volume.
4. Explain melting and boiling in terms of interparticle
attraction, interparticle spacing, and the thermal energy of particles, using
ice, water, and water vapour as an example.
• Ice (solid) at low temperature has particles with low
thermal energy, strong interparticle attraction, and minimum spacing —
particles are fixed in position and can only vibrate.
• At the melting point (0°C), thermal energy supplied is
used to overcome the interparticle attraction; particles begin to move out of
their fixed positions, and interparticle spacing increases slightly as ice changes
into liquid water.
• Interestingly, ice is an exception among solids — its
particles are farther apart than in liquid water, which is why ice floats on
water.
• As water is heated further, particles gain more thermal
energy and move more vigorously, gradually weakening the interparticle
attraction further.
• At the boiling point (100°C), particles gain enough energy
to overcome interparticle attraction almost completely, escaping the liquid
state; interparticle spacing becomes maximum and attraction becomes negligible
as water changes into water vapour (steam).
5. Describe the activities used to demonstrate diffusion
in liquids (potassium permanganate in water) and in gases (fragrance of an
incense stick), and explain what each activity tells us about particle
movement.
• Activity 7.8 — a few grains of potassium permanganate are
dropped into water; pink streaks initially spread from the grain, and
eventually the entire water turns uniformly pink, showing water particles are
in constant motion, pulling out and spreading the potassium permanganate
particles.
• Repeating this with hot, room-temperature, and ice-cold
water shows the colour spreads fastest in hot water, slower at room
temperature, and slowest in ice-cold water — proving particle movement increases
with rising temperature.
• Activity 7.9 — lighting an incense stick in one corner of
a room causes the fragrance to be felt near the stick at first, then throughout
the entire room, showing air particles are constantly moving and carry
fragrance particles with them.
• Both activities demonstrate diffusion — the spontaneous
spreading of particles due to their continuous, random motion.
• Diffusion occurs much faster in gases than in liquids,
because gas particles have far greater interparticle spacing and much weaker
(negligible) interparticle attraction compared to liquid particles.
6. Explain why sugar and salt dissolve in water, but sand
does not. Describe the activity used to demonstrate the presence of
interparticle spaces in liquids.
• Sugar and salt are soluble solids — water particles are
able to overcome the interparticle attraction holding their constituent
particles together, pulling these particles apart.
• The separated constituent particles of sugar/salt then
occupy the interparticle spaces between water particles, forming a solution in
which they are no longer visible but can be detected (by taste, for example).
• Sand is an insoluble solid — its constituent particles are
held together by interparticle attraction too strong for water particles to
overcome, so sand does not dissolve and instead settles down.
• Activity 7.7 demonstrates interparticle spaces in liquids:
water is marked at level A, sugar is added and the new level marked B, then the
mixture is stirred until the sugar dissolves and the level marked again as C.
• Since level C is found to be less than level B (the sum of
the separate volumes of water and sugar),
this proves that dissolved sugar particles occupy spaces
between water particles rather than adding fully to the total volume —
confirming the existence of interparticle spaces in liquids.
7. Explain the three states of matter (solid, liquid, and
gas) in terms of shape, volume, interparticle spacing, interparticle
attraction, and movement of particles, giving one everyday example of each.
• Solid — definite shape and definite volume; minimum
interparticle spacing; maximum interparticle attraction; particles can only
vibrate about fixed positions; example — an iron nail.
• Liquid — no fixed shape but a definite (fixed) volume;
interparticle spacing slightly more than in solids; interparticle attraction
slightly weaker than in solids; particles can move, but only within a limited
space; example — water.
• Gas — no fixed shape and no fixed volume; maximum
interparticle spacing; minimum/negligible interparticle attraction; particles
move freely in all available space; example — air.
• This progression shows a clear trend: as we move from
solid to liquid to gas, interparticle attraction decreases and interparticle
spacing increases, giving particles progressively greater freedom of movement.
• It is this freedom of movement (or lack of it) that
ultimately explains why solids hold their shape, liquids flow but keep their
volume, and gases both flow and expand to fill their container.
8. Using Table 7.1 (melting points of ice, urea, and
iron) as reference, explain why some solids melt at low temperatures while
others melt only at very high temperatures.
• The melting point of a solid depends on the strength of
the interparticle attraction holding its constituent particles together.
• Ice has relatively weak interparticle forces of
attraction, so only a small amount of thermal energy
(heating to just 0°C) is needed to overcome these forces and
allow the particles to move out of their fixed positions.
• Urea has somewhat stronger interparticle attraction than
ice, requiring a higher temperature (133°C) before its particles gain enough
thermal energy to overcome these forces and melt.
• Iron has very strong interparticle (metallic) attraction,
so a very large amount of thermal energy — a temperature as high as 1538°C — is
needed to overcome these forces and melt it.
• Thus, the melting point of a solid is a direct indicator
of the strength of its interparticle attractive forces: the stronger the
attraction, the higher the melting point.
9. Explain the concepts of interparticle spaces and
interparticle attractions, and how they together decide whether a substance
exists as a solid, liquid, or gas. Include the role of thermal energy in your
explanation.
• All matter is made up of constituent particles held
together by attractive forces called interparticle attractions, with empty
interparticle spaces existing between them.
• In solids, interparticle spacing is minimum and
interparticle attraction is maximum, so particles remain fixed in position,
giving solids a definite shape and volume.
• In liquids, interparticle spacing is slightly more and
interparticle attraction is slightly weaker, allowing particles to move within
a limited space; liquids therefore have a fixed volume but no fixed shape.
• In gases, interparticle spacing is maximum and
interparticle attraction is negligible, so particles move freely in all
directions; gases have neither a fixed shape nor a fixed volume.
• The physical state that a substance exists in is
ultimately decided by the thermal energy of its particles: low thermal energy
allows strong interparticle attraction to dominate (solid state), while increasing
thermal energy (through heating) progressively overcomes this attraction,
converting the substance from solid to liquid (at the melting point) and then
to gas (at the boiling point).
10. Design and explain a set of simple experiments that a
student could perform at home to demonstrate the particulate nature of matter
in solids, liquids, and gases.
• Experiment 1 (solid) — break a piece of chalk repeatedly
and grind it into a fine powder using two spoons or a mortar and pestle;
observing the powder under a magnifying glass shows chalk is made up of many
tiny particles, and that grinding is only a physical change.
• Experiment 2 (liquid) — dissolve two teaspoons of sugar or
salt in a glass of water without stirring and taste the top layer, then stir
and taste again; the change in taste, despite no visible particles, shows that
constituent particles spread through the interparticle spaces of the liquid.
• Experiment 3 (gas) — light an incense stick (or use a few
drops of perfume) in one corner of a room and observe how the fragrance reaches
every corner within a few minutes, showing that gas particles move freely,
quickly, and in all directions.
• Experiment 4 (compressibility) — using a syringe without a
needle, trap some air by blocking the open end with a thumb and push the
plunger; then repeat with water instead of air, comparing how easily each
compresses.
• Together, these four simple experiments illustrate the
particulate nature of matter across all three states — showing that matter is
made of tiny particles, that interparticle spaces exist, and that interparticle
attraction and spacing differ between solids, liquids, and gases.
Section E: Assertion-Reason
Questions (1 Mark Each)
(a) Both A and R true, R explains A | (b) Both A and R true,
R does not explain A | (c) A true, R false | (d) A false, R true
1. Assertion: Grinding chalk into fine powder is a
chemical change.
Reason: Grinding chalk changes only the size of its
particles; the chalk does not change into a new substance.
Answer: (d) — A is false — grinding chalk is a physical
change, not a chemical change. R is true and correctly explains why it is a
physical change.
2. Assertion: Sugar particles cannot be seen after
dissolving in water, but their presence can be sensed by taste.
Reason: When sugar dissolves in water, it breaks into
constituent particles that occupy the interparticle spaces of water.
Answer: (a) — Both A and R are true, and R correctly
explains why sugar's presence can still be detected by taste.
3. Assertion: Solids have a definite shape and volume.
Reason: In solids, the interparticle attractions are very
strong and hold the particles in fixed positions.
Answer: (a) — Both A and R are true, and R correctly
explains why solids keep a definite shape and volume.
4. Assertion: Liquids have no fixed shape but have a
fixed volume.
Reason: In liquids, the interparticle attractions are
completely negligible.
Answer: (c) — A is true — liquids do have a fixed volume but
no fixed shape. R is false — interparticle attraction in liquids is only
slightly weaker than in solids, not negligible (it is gases that have
negligible attraction).
5. Assertion: Gases can be compressed easily, but liquids
like water are practically incompressible.
Reason: Gases have large interparticle spaces, while liquids
have very little space between their constituent particles.
Answer: (a) — Both A and R are true, and R correctly
explains the difference in compressibility.
6. Assertion: Ice floats on water.
Reason: In ice, the constituent particles are farther apart
than in liquid water.
Answer: (a) — Both A and R are true, and R correctly
explains why ice is less dense and floats on water.
7. Assertion: The spreading of smoke from one gas jar
into another shows that gas particles are completely stationary.
Reason: Gas particles move freely and constantly in all
directions.
Answer: (d) — A is false — the spreading of smoke actually
shows gas particles are NOT stationary. R is true and gives the correct
explanation for why smoke spreads.
8. Assertion: Potassium permanganate spreads faster in
hot water than in cold water.
Reason: The movement of water particles increases with an
increase in temperature.
Answer: (a) — Both A and R are true, and R correctly
explains why the spreading is faster in hot water.
9. Assertion: Evaporation and boiling are exactly the
same process.
Reason: Evaporation occurs only at the surface of a liquid
at any temperature, while boiling occurs throughout the liquid at a fixed temperature.
Answer: (d) — A is false — evaporation and boiling are
different processes. R is true and correctly explains the difference between
them.
10. Assertion: Acharya Kanad proposed that matter is made
up of indivisible, eternal particles called Parmanu.
Reason: This idea was recorded in his work called the
Vaisheshika Sutras.
Answer: (a) — Both A and R are true, and R correctly
identifies the work in which Kanad's idea was recorded.
A. Short Questions with Answers
1. What is matter?
Answer: Matter is anything that has mass and occupies
space (volume). Light, heat, electricity, thoughts and emotions are not matter.
2. What is a mixture?
Answer: A mixture is formed when two or more
substances are combined, but each substance retains its own identity and
chemical nature. The components do not react chemically with each other.
3. Give two examples of mixtures.
Answer:
- Sugar
dissolved in water
- Salad
containing green gram, chickpeas, onion and tomato.
4. What is a homogeneous mixture?
Answer: A homogeneous mixture is a uniform mixture in
which the components are evenly distributed and cannot be distinguished
separately. For example, sugar dissolved in water.
5. What is a heterogeneous mixture?
Answer: A heterogeneous mixture is a non-uniform
mixture in which the components are visibly separate or unevenly distributed.
For example, sprout salad.
6. Is air a mixture?
Answer: Yes. Air is a homogeneous mixture of gases
such as nitrogen, oxygen, argon, carbon dioxide and water vapour.
7. How can we confirm the presence of carbon dioxide in
air?
Answer: When lime water is exposed to air, it turns
milky because carbon dioxide reacts with calcium hydroxide to form insoluble
calcium carbonate and water. This confirms the presence of carbon dioxide in
air.
8. What does the black-sheet activity show?
Answer: It shows that dust particles are suspended in
the air. The nature and number of dust particles may vary from place to place
and from time to time.
9. What is a pure substance?
Answer: A pure substance consists of the same type of
particles throughout and cannot be separated into other kinds of matter by
physical means.
10. What are the two constituents of water?
Answer: Water is composed of hydrogen and oxygen.
11. What is an element?
Answer: An element is a pure substance made up of
identical particles (atoms) that cannot be broken down into simpler substances
by chemical means.
12. Give examples of elements.
Answer: Hydrogen, oxygen, gold, silver, sulfur and
carbon are examples of elements.
13. What are molecules?
Answer: Two or more atoms of many elements combine to
form a stable particle of that element called a molecule. Examples include H₂
and O₂.
14. Name the three types of elements based on their
properties.
Answer:
- Metals
- Non-metals
- Metalloids
15. What is a compound?
Answer: A compound is a pure substance formed when
two or more different elements combine chemically in a fixed ratio.
16. How are the properties of a compound different from
its constituent elements?
Answer: A compound has properties that are different
from those of the elements from which it is formed.
17. What is the ratio of hydrogen and oxygen in water?
Answer: Hydrogen and oxygen combine in the ratio 2:1
to form water (H₂O).
18. What is sodium chloride?
Answer: Sodium chloride (table salt) is a compound
formed when sodium and chlorine combine chemically in a 1:1 ratio.
19. What happens when sugar is heated?
Answer: Sugar turns brown and produces droplets of
water. Carbon (charcoal) is left behind. Thus, sugar decomposes into carbon and
water on heating.
20. Why is sugar not an element?
Answer: Sugar decomposes on heating to form carbon
and water. Since water contains hydrogen and oxygen, sugar contains carbon,
hydrogen and oxygen. Therefore, sugar is a compound, not an element.
21. What is Sample A in the iron and sulfur experiment?
Answer: Sample A is a mixture of iron and sulfur.
Both substances retain their individual properties and can be seen separately.
22. Is Sample A a uniform or non-uniform mixture?
Answer: Sample A is a non-uniform (heterogeneous)
mixture because iron and sulfur can be observed as separate substances.
23. How can iron be separated from sulfur in Sample A?
Answer: Iron can be separated from sulfur using a
magnet because iron is attracted to the magnet while sulfur is not.
24. What is Sample B?
Answer: Sample B is iron sulfide, a compound
formed by heating iron and sulfur.
25. Is Sample B attracted by a magnet?
Answer: No. Sample B, iron sulfide, is not attracted
by a magnet.
26. What happens when Sample B reacts with dilute
hydrochloric acid?
Answer: Iron sulfide reacts with dilute hydrochloric
acid to form iron chloride and hydrogen sulfide gas. The gas has a
rotten-egg-like odour.
27. What are minerals?
Answer: Minerals are naturally occurring, solid
substances found in the Earth. They generally have a fixed chemical composition
and are often compounds, though some are native elements.
28. What are native minerals?
Answer: Native minerals are pure elements found
naturally in the Earth, such as gold, silver and copper.
B. Long Questions with Answers
1. Differentiate between a mixture and a compound.
Answer:
|
Mixture |
Compound |
|
A mixture contains two or more substances combined
together. |
A compound is formed when two or more different elements
combine chemically. |
|
Components retain their individual properties. |
The compound has properties different from its constituent
elements. |
|
Components are not chemically combined. |
Elements are chemically combined. |
|
Components can often be separated by physical methods. |
The constituent elements cannot be separated by simple
physical methods. |
|
The components need not be present in a fixed ratio. |
Elements are present in a fixed ratio. |
|
Example: iron and sulfur mixture. |
Example: iron sulfide. |
The chapter demonstrates this clearly through the
iron–sulfur experiment. In Sample A, iron and sulfur retain their properties
and can be separated. After heating, Sample B (iron sulfide) has completely
different properties and the iron and sulfur can no longer be separated.
2. Explain how the iron and sulfur experiment
demonstrates the difference between a mixture and a compound.
Answer:
Iron filings and sulfur powder are first mixed together to
form Sample A. In Sample A, the black iron and yellow sulfur can be seen
separately. Iron retains its magnetic property and can be separated using a
magnet. When dilute hydrochloric acid is added, iron reacts to produce hydrogen
gas, while sulfur remains unchanged. Thus, Sample A is a mixture in which both
substances retain their individual properties.
When Sample A is heated, a black substance called iron
sulfide (Sample B) is formed. It has a uniform colour and texture, is not
attracted by a magnet, and has properties different from those of iron and
sulfur. Iron and sulfur can no longer be separated from it. Therefore, Sample B
is a compound.
3. Explain how water can be shown to be a compound.
Answer:
Water can be broken down into two different gases by passing
electricity through it. In the experiment, water containing a few drops of
dilute sulfuric acid is placed in a setup with two test tubes and a battery.
Gas bubbles form at both terminals.
After some time, different volumes of gases are collected in
the two test tubes. When a burning candle is brought near the gases, one gas
produces a pop sound, confirming hydrogen, while the other makes the
flame glow brighter, confirming oxygen.
Therefore, water is composed of two different constituents—hydrogen
and oxygen.
4. Explain the classification of pure substances.
Answer:
Pure substances consist of only one kind of particle and
cannot be separated into other kinds of matter by physical means. They are
classified into elements and compounds.
Elements are pure substances made up of identical
particles (atoms) and cannot be broken down into simpler substances by chemical
means. Examples include hydrogen, oxygen, gold, silver, sulfur and carbon.
Compounds are pure substances formed when two or more
different elements combine chemically in a fixed ratio. Their properties are
different from those of their constituent elements. Water and sodium chloride
are examples of compounds.
5. Explain the different types of mixtures with examples.
Answer:
Mixtures can be classified into two types:
1. Homogeneous mixture:
It is a uniform mixture in which the components are evenly distributed and
cannot be distinguished separately. Sugar dissolved in water is an
example.
2. Heterogeneous mixture:
It is a non-uniform mixture in which the components are visibly separate or
unevenly distributed. Sprout salad is an example.
6. Explain why air is considered a mixture.
Answer:
Air is considered a mixture because it contains several
gases, including nitrogen, oxygen, argon, carbon dioxide and water vapour.
These gases retain their individual identities and are not chemically combined
with one another.
Air is a homogeneous mixture under standard
conditions because its gaseous components are uniformly distributed.
The presence of carbon dioxide can be demonstrated by
exposing lime water to air. The lime water turns milky because carbon dioxide
reacts with calcium hydroxide to form calcium carbonate and water.
7. Explain the importance and uses of elements, compounds
and mixtures in everyday life.
Answer:
Elements, compounds and mixtures are found all around us and
have many practical applications.
- Air
is a mixture of gases.
- Water
is a compound.
- Iron
and aluminium are elements used in bridges and vehicles.
- Chemists
use knowledge of how elements combine to make compounds such as medicines,
vaccines and fertilisers.
- Material
scientists use compounds and mixtures to make special materials such as
alloys.
- Stainless
steel, for example, is an alloy that is stronger than pure iron.
8. What are minerals? Explain with examples.
Answer:
Minerals are naturally occurring solid substances found in
the Earth. They generally have a fixed chemical composition. Many minerals are
compounds, while some are naturally occurring pure elements called native
minerals.
Examples of native minerals include gold, silver and
copper. Examples of minerals that are compounds include quartz, calcite,
mica and olivine.
Minerals are also used to make everyday materials. For
example, cement is made from minerals such as calcite, quartz, alumina and iron
oxide, while talcum powder is made from the mineral talc.
C. Important “Think and Answer”
Questions
1. Which entities consist of matter and which do not?
Answer: Anything that has mass and occupies space is
matter. Therefore, physical substances such as water, air, books, stones and
objects are matter. Light, heat, electricity, thoughts and emotions are not
matter.
2. How can elements be combined to form a compound?
Answer: Two or more different elements combine chemically
in a fixed ratio to form a compound. The resulting compound has properties
different from those of its constituent elements.
3. How could a compound that absorbs carbon dioxide from
air help solve environmental challenges?
Answer: Based on the chapter's discussion of carbon
dioxide in air, a compound that absorbs carbon dioxide could help reduce the
amount of carbon dioxide present in the atmosphere. This could contribute to
addressing environmental challenges associated with excess atmospheric carbon
dioxide. The chapter raises this as a Probe and Ponder question but does
not provide a detailed answer.
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