Frank Brothers Solutions for ICSE Class 9 Chemistry Chapter 1 Matter And Its Composition

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Question 1:
Answer: Matter is anything around us which occupies space and has mass. Example - Coal, Copper, Water, Oxygen, Kerosene
Key: Matter occupies space and has mass.
Everything you touch, eat, or breathe is considered matter because it is made of physical particles. Even invisible air is matter because it takes up space inside a balloon and has weight.
Teacher's Tip: Think of the "M&M" rule: Matter must have Mass.
Exam Tip: Always include at least two examples when defining matter to show a complete understanding.

Question 2:
Answer: The conditions for something to be called matter are -
1. It should occupy space.
2. It should have mass.
Occupying space means that matter has a specific volume that cannot be shared by something else at the same time. Having mass means that the object contains a certain amount of material that can be measured on a scale.
Teacher's Tip: Remember "S.M." for Space and Mass to quickly recall the two conditions.
Exam Tip: If asked for the characteristics of matter, stating these two conditions is mandatory for full marks.

Question 3:
Answer: Light and sound are not considered to be matter because they neither have mass nor do they occupy space.
Light and sound are forms of energy, which are different from physical objects. Energy can move through matter, but it does not have weight or a physical size of its own.
Teacher's Tip: Energy is like the "power" that moves things, while matter is the "thing" being moved.
Exam Tip: Mention that light and sound are "forms of energy" to explain why they don't fit the definition of matter.

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Question 4:
Answer: Solid:
1. The particles are held together by strong intermolecular forces and have minimum intermolecular space.
2. Solids have definite mass, shape and volume.
Liquid:
1. The intermolecular forces of liquid molecules are intermediate of molecules of solids and gases while intermolecular spaces are greater than in solids.
2. Liquids have definite mass and volume but not definite shape. They take the shape of the container.
Gas:
1. The particles are held together by very weak intermolecular forces while intermolecular spaces are much greater than in solids.
2. Gases have definite mass but not definite shape and volume. They take the shape of the container.
Particles in a solid are like students sitting tightly in their chairs, while in a gas, they are like kids running freely on a playground. Liquids fall in between, allowing particles to slide past each other while still staying close.
Teacher's Tip: Remember "Strong, Some, Small" to describe the forces in Solids, Liquids, and Gases.
Exam Tip: Use a comparative approach when describing the three states to highlight the differences in shape and volume.

Question 5:
Answer: Two reasons for saying that wood is a solid are -
1. Wood has definite mass and shape.
2. Their intermolecular forces are very strong so they cannot flow.
Because wood maintains its shape regardless of the container it is placed in, it fits the primary definition of a solid. Its internal particles are packed so closely that they cannot move around, preventing it from flowing like water.
Teacher's Tip: If you can't pour it and it doesn't change shape on its own, it's a solid.
Exam Tip: Use the term "intermolecular forces" to provide a scientific explanation for why a substance cannot flow.

Question 6:
Answer: The particles of gases are separated from each other by large spaces and intermolecular forces of attraction are the weakest in gases. They have least density. So, they can flow easily. Hence, gases have no fixed shape and volume.
Key: Intermolecular forces of attraction are the weakest in gases.
Gas particles have so much energy that they overcome any attraction to each other and fly apart in all directions. This allows them to fill up any container, no matter how big or small it is.
Teacher's Tip: Think of gas particles as "social distancers" who like to stay as far apart as possible.
Exam Tip: Emphasize "weakest forces" and "large spaces" together to explain the lack of fixed shape in gases.

Question 7:
Answer: 1. Gases
2. Solid
3. Solid
These identifications are based on observing how different materials occupy space and maintain their structures. Recognizing these states helps us understand how matter behaves in our daily environment.
Teacher's Tip: Practice identifying the state of everything you see around your classroom.
Exam Tip: Double-check the properties of a substance before classifying its state to avoid silly mistakes.

Question 8:
Answer: Properties - Solids - Liquids - Gases
1. State of packing: Solids - The particles are closely packed and their positions are also fixed. Liquids - The particles are loosely packed and their positions are not fixed. Gases - The molecules are wide apart and their positions are also not fixed.
2. Energy associated: Solids - Particles can vibrate only to and fro about their mean positions. Therefore, they have small kinetic energy due to their motion. Liquids - The particles can move about more freely and have considerable kinetic energy due to their motion. Gases - The particles move about freely and have maximum kinetic energy due to their motion.
3. Intermolecular forces: Solids - The particles are held together by strong intermolecular forces. Liquids - The particles are held together by weak intermolecular forces. Gases - The particles are held together by very weak intermolecular forces.
4. Physical features: Solids - Solid has a crystalline structure with both definite size and definite shape. Liquids - Liquid does not have a definite shape but has definite volume and can flow from higher to lower level. Gases - Gas has neither definite shape nor a definite volume but can flow and is easily compressible.
This comparison shows that as energy increases from solid to gas, the order and structure of the particles decrease. While solids are rigid, gases are highly energetic and can be squeezed into very small spaces.
Teacher's Tip: Kinetic energy is the "energy of movement" - gases have the most because they move the fastest.
Exam Tip: For comparison questions, always include "packing" and "intermolecular forces" as they are the most important scientific points.

Question 9:
Answer: 1. gases
2. strong
3. sublimation
4. Condensation
5. gaseous
These terms describe the behavior of matter and the specific names for the transitions between different states. Understanding these vocabulary words is essential for explaining chemical and physical changes.
Teacher's Tip: Associate "Sublimation" with "Dry Ice" to remember it skips the liquid phase.
Exam Tip: Be careful with spelling for terms like "sublimation" and "condensation" to ensure full marks.

Question 10:
Answer: The postulates of the kinetic theory of matter -
1. Composition of Matter: Matter, whether in the solid, liquid or gaseous state, is composed of very small particles which may be molecules, atoms or ions.
2. Arrangement of Particles: These particles have spaces lying between them and these spaces are referred to as intermolecular spaces or interparticle spaces.
3. Forces of Attraction: The forces of attraction between the molecules of a given substance are called intermolecular forces. The magnitude of this force depends upon the state of the substance and on the magnitude of the intermolecular spaces. As the intermolecular space increases, the intermolecular force decreases.
4. Motion of the constituent particles: The particles are always in a state of motion. In solids, they vibrate about their mean positions and in liquids and gases, they move randomly.
5. The kinetic energy of the particles increases with rise in temperature. As the temperature is increased, the particles undergo motion more vigorously and more randomly.
This theory explains that all matter is alive with constant motion, even if it looks still to our eyes. Heating a substance gives these tiny particles more "fuel" to move faster and push away from each other.
Teacher's Tip: Think of temperature as a "speedometer" for particles - higher temp means higher speed!
Exam Tip: Memorize the relationship: "Space Increases = Force Decreases" as it is a core concept of the kinetic theory.

Question 11:
Answer: 1. Solid to liquid state: The conversion of a substance from the solid state to liquid state at a particular temperature is called melting or fusion. The heat energy supplied to the solid is absorbed by its molecules to gain kinetic energy. The kinetic energy increases the rate of vibration of the molecules. The force of attraction thus no longer holds the molecules close together and the solid gets change into liquid.
2. Gas to liquid: The conversion of a substance from the gaseous state to its liquid state at a particular temperature is called condensation or liquefaction. On cooling, the gas molecules loose their kinetic energy in the form of lost heat and so molecular motion slows down. Decreased molecular motion causes a decrease in intermolecular space. The molecules come very close and the force of attraction between them correspondingly increases and the gas gets change into liquid.
3. Liquid to gaseous state: The heat energy supplied to the liquid is absorbed by its molecules to gain kinetic energy and therefore the molecules move faster. This increases the intermolecular space. The intermolecular force of attraction decreases and liquid changes into gaseous state.
4. Liquid to solid state: The conversion of a substance from the liquid state to solid state by cooling is called freezing. On cooling a liquid, the kinetic energy of the molecule is decreased. Due to decreased kinetic energy, the molecules cool down and come closer, thus reducing the intermolecular spaces. The force of attraction between the molecules thus increases. Now, the molecules are no longer in a position to be free or to migrate and liquid changes into a solid.
Changing the state of matter is all about adding or removing heat energy to control how fast particles move. When you cool a gas, you are essentially "slowing down" the particles until they are forced to huddle back together into a liquid.
Teacher's Tip: Melting and Freezing happen at the same temperature - it just depends on if you are adding or taking away heat!
Exam Tip: Always use the term "kinetic energy" when explaining why a substance changes its state upon heating or cooling.

Question 12:
Answer: 1. Freezing: The process of changing a liquid into a solid by cooling is called freezing. Freezing means solidification. It occurs at a definite temperature called freezing point.
2. Evaporation: The phenomenon involving the change of a substance from the liquid state to the gaseous state at room temperature or at any other temperature below its boiling point is called vaporization or evaporation.
3. Boiling point: The temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure is called boiling point of the liquid.
4. Melting point: The temperature at which a solid substance changes into its liquid state at 1 atmospheric pressure is called the melting point of that substance.
These definitions describe specific scientific milestones for matter as it reacts to temperature. Unlike boiling, evaporation happens slowly and only at the surface of a liquid, even on a cool day.
Teacher's Tip: Boiling is "Fast and Everywhere" (bubbles), while Evaporation is "Slow and Surface Only."
Exam Tip: Include "at atmospheric pressure" when defining boiling or melting points to show high scientific accuracy.

Question 13:
Answer: 1. Size of naphthalene balls decreases - Sublimation
2. Drying of wet clothes - Evaporation
3. Wax melts in the sun - Melting
4. Formation of clouds - Evaporation and Condensation
These daily life examples show how matter is constantly switching between states all around us. For example, cloud formation is a two-step process where water first turns to gas and then back into tiny liquid droplets high in the sky.
Teacher's Tip: Look for "invisible" changes to find examples of evaporation and sublimation.
Exam Tip: For "cloud formation," make sure to mention both processes (evaporation and condensation) for full marks.

Question 14:
Answer: Three compounds which are sublimate are 1. Camphor, 2. Naphthalene, 3. Iodine
Sublimates are special substances that disappear into the air without leaving a puddle behind. This happens because their particles gain enough energy to break completely free from the solid state instantly.
Teacher's Tip: Think of these as "Liquid-Skippers" because they skip the middle state of matter.
Exam Tip: Memorizing these three specific examples will help you answer many different types of chemistry questions.

Question 15:
Answer: ‘States of matter triangle’ shows inter-conversion of states of matters.
The triangle illustrates the cyclical nature of physical changes, connecting solid, liquid, and gas through various processes. It serves as a visual map showing how energy flows into or out of a system to create change.
Teacher's Tip: Follow the arrows: arrows pointing "up" (toward gas) usually mean adding heat, arrows "down" mean cooling.
Exam Tip: Be ready to draw and label this triangle, including terms like "Vaporisation" and "Liquefaction."

Question 16:
Answer: The process by which a liquid slowly converts into vapour state at a temperature below its boiling point is called evaporation. The heat energy is absorbed by the liquid to convert it into vapour state. So, loss of heat causes cooling.
When you sweat, the evaporation of moisture from your skin steals heat from your body, making you feel cooler. This is why a breeze feels so good on a hot day—it speeds up this heat-stealing process.
Teacher's Tip: Remember: Evaporation = Cooling. This is why we use earthen pots to keep water cold.
Exam Tip: Explain that heat is "absorbed from the surroundings" to justify why evaporation leads to a decrease in temperature.

Question 17:
Answer: 1. True
2. True
3. False
4. True
Determining the truth of these statements requires applying the rules of the kinetic theory of matter. For example, it is true that heating a substance increases the speed of its internal particles.
Teacher's Tip: Read True/False questions carefully; sometimes one "Not" or "Always" can change the whole answer.
Exam Tip: If a statement is false, try to mentally correct it to confirm why it doesn't fit the scientific facts.

Question 18:
Answer: “In all physical and chemical changes, the total mass of the reactants is equal to that of the products”. So, in other words matter can neither be created nor destroyed.
This law proves that even if an object changes its look or turns into a gas, the total amount of "stuff" remains exactly the same. Nature is a master recycler, simply rearranging atoms into new patterns without losing any.
Teacher's Tip: Think of a LEGO set; you can build a car or a house, but you still have the same number of bricks.
Exam Tip: Memorize the phrase "mass of reactants equals mass of products" as it is the standard definition for this law.

Question 19:
Answer: Physical change: A piece of ice is taken in a small conical flask. It is well corked and weighed. The flask is now heated gently to melt the ice into water. Ice →{heat} water. The flask is again weighed. It is found that there is no change in the weight through a physical change has taken place. Chemical change: Decomposition of Mercuric oxide - 100 g of mercuric oxide when heated in a closed tube, decomposed to produce 92.6 g of mercury and 7.4 g of oxygen gas. HgO(s) → Hg(l) + 1/2 O₂g. 100 g -> 92.6 g + 7.4 g. Thus during the above decomposition reaction, matter is neither gained nor lost.
These experiments provide concrete evidence that mass stays constant during any transformation. Whether melting ice or breaking down a chemical compound, if you keep the container sealed, the scale will always show the same number.
Teacher's Tip: A "closed tube" or "corked flask" is the key to proving this law because it prevents gas from escaping.
Exam Tip: Always include the weights (e.g., 92.6 g + 7.4{ g} = 100 g to prove the math behind the law.

Question 20:
Answer: 1. Matter, 2. Solid, 3. Gas, 4. Solid, 5. Gas, 6. Gas, 7. Liquid, 8. Fluid, 9. Melting, 10. Vaporization
This list provides the fundamental terminology used to categorize the physical world and its transitions. From knowing that liquids and gases are both "fluids" to defining the process of melting, these terms are the building blocks of chemistry.
Teacher's Tip: A "Fluid" is anything that can flow—this includes both liquids and gases!
Exam Tip: For one-word answers, ensure your handwriting is very clear so the examiner doesn't misread your scientific terms.