# Matter In Our Surroundings NCERT Solutions

Matter In Our Surroundings NCERT Solutions – Here are simplified solutions for Class 9 Science Chapter 1, “Matter in Our Surroundings.” This chapter covers various topics related to matter, its properties, and changes it undergoes. The solutions provide easy-to-understand explanations, step-by-step guidance, and relevant images to help students comprehend the concepts better. These solutions are designed for students who use the NCERT textbook to study science.

Contents

## Matter In Our Surroundings NCERT Solutions

##### Q. Which of the following are matter?Chair, air, love, hate, smell, thought, almonds, cold-drink, cold, smell of perfume.

Answer – The matter is anything that has mass and takes up space. Based on this definition, the following are matters:

• Chair: It has mass and takes up space.
• Air: It has mass and takes up space.
• Almonds: They have mass and take up space.
• Cold-drink: It has mass and takes up space.
• Smell of perfume: It involves particles moving through the air, so it has mass and takes up space.
##### Q. Give reasons for the following observation:The smell of hot, sizzling food may be several meters away, But, you must come close to smell cold food.

Answer – Hot food molecules have more kinetic energy than cold food molecules, so they evaporate faster and spread over a larger area, reaching you several meters away. Cold food molecules have less kinetic energy, so they evaporate slower and don’t spread as far, requiring you to be closer to smell them.

##### Q. A diver can easily cut through the water in a pool. Which property of matter observation shows?

Answer – The ease with which the diver is able to cut through the water in the swimming pool is due to the low intermolecular forces of attraction between water molecules. This property of water allows it to flow easily and is responsible for the diver’s ability to move through it with minimal resistance.

##### Q. What distinguishing features do matter particles have?

Answer – Characteristics of the particles of matter are –

1. We refer to the space between matter particles as intermolecular space. Depending on the condition of the matter, this space can differ, with solids having the least and gases having the greatest.
2. Intermolecular forces of attraction also affect the behaviour and characteristics of matter particles. Depending on the type of particle and the distance between them, these forces might be weak or powerful.
3. Matter particles always move because they have kinetic energy. The temperature is one factor that affects this mobility randomly, with higher temperatures causing more movement of the particles.
##### Q. Density is the measure of a substance’s mass per unit volume.(density = mass/volume).Arrange the following in increasing order: air, honey, exhaust from chimneys, chalk, water, cotton and iron.

Air < Cotton < Exhaust from chimneys < Water < Honey < Chalk < Iron

##### (a) Tabulate the variations in the properties of states of matter.(b) Comment upon the following: rigidity, compressibility, fluidity, , kinetic energy filling a gas container, shape and density.

(a)

(b)

• Rigidity: The ability of a substance to resist deformation or movement. Solids have high rigidity.
• Compressibility: The ability of a substance to be compressed or squeezed. Gases have high compressibility.
• Fluidity: The ability of a substance to flow or take the shape of the container it is in. Liquids and gases have fluidity.
• Filling a gas container: Gases will completely fill any container they are placed in, regardless of the shape or size of the container.
• Shape: Solids have a definite shape, while liquids and gases take the shape of their container.
• Kinetic energy: The energy that particles possess due to their motion. The kinetic energy of particles increases as temperature increases.
• Density: The mass per unit volume of a substance. Solids are generally the densest, followed by liquids, and then gases.
##### Q. Give reasons(a) A gas fills completely the container in which it is contained.(b) A gas experience pressure on the walls of the container.(c) A wooden table need to be called a solid.(d) We can easily move our hand in air but a karate master is required to move a hand through a solid piece of wood.

(a) A gas fills completely the vessel in which it is kept because gases have weak intermolecular forces and the particles move randomly in all directions. Therefore, they tend to fill the available space completely.

(b) A gas exerts pressure on the walls of the container because gas particles are in constant random motion, and they collide with the walls of the container, which results in pressure on the walls.

(c) A wooden table should be called a solid because it has a definite shape and volume due to strong intermolecular forces between its particles. The molecules of a solid are closely packed and have minimum intermolecular spaces.

(d) We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert because solids have strong intermolecular forces, and the molecules are closely packed. It requires a significant amount of force to break the intermolecular forces and move the particles apart. A karate expert has trained their muscles to generate a large amount of force, which helps them to break the intermolecular forces and move their hand through the solid block of wood.

##### Q. Liquids generally have less density as compared to solid. But ice floats on water. Find out why.

Answer – Due of its lower density than liquid water, ice floats on water. This is because ice has a special structural makeup. When the molecules are closely clustered, a solid has a smaller volume and a higher density. Ice, on the other hand, has molecules that arrange themselves into a crystal lattice structure with empty spaces in between. As a result, the ice’s density decreases and its overall volume increases. Ice floats on liquid water because liquid water is denser than ice. This characteristic of ice is important because it enables the preservation of aquatic life over the winter.

##### Q. Convert temperature to Celsius scale:(a) 300 K (b) 573 K

(a) To convert 300 K to Celsius scale, we need to subtract 273.15 from it.

Therefore, 300 K – 273.15 = 26.85 °C

(b) To convert 573 K to Celsius scale, we need to subtract 273.15 from it.

Therefore, 573 K – 273.15 = 299.85 °C

##### Q. What physical state is water in at the following:(a) 250°C (b) 100°C

Answer – (a) 250°C = gas (b) 100°C liquid as well as gas

##### Q. Why does the temperature stay the same during the change of state for any substance?

Answer – During a change of state, such as from a solid to a liquid or from a liquid to a gas, the temperature of a substance remains constant because the energy being added or removed is used to overcome the intermolecular forces that hold the substance in its current state, rather than increasing or decreasing the kinetic energy of the molecules.

##### Q. Suggest a technique for liquefying atmospheric gases?

Answer – One common method to liquefy atmospheric gases is through a process called cryogenic distillation, which involves cooling the gases to very low temperatures and then separating them based on their boiling points. The steps involved in this process are as follows:

1. Compress the atmospheric gases, such as nitrogen, oxygen, and argon, to increase their pressure and make them easier to liquefy.
2. Cool the compressed gases using a refrigeration system, such as a Joule-Thomson expansion, to reduce their temperature to below their boiling points.
3. Separate the cooled gases based on their boiling points using a distillation column. The column is typically filled with packing material to increase the surface area for heat exchange and promote separation of the different components. The lower boiling gases will evaporate first, followed by the higher boiling gases, with each component being collected separately as a liquid.
4. Further cool and purify the separated gases to remove any remaining impurities and improve their quality as commercial products.
##### Q. Why does a desert cooler cool more effectively in the desert on a hot, dry day?

Answer – A desert cooler works best in hot and dry climates because the rate of evaporation is directly proportional to the dryness of the air. In a hot and dry environment, the air has low humidity, which means that it has a high capacity to absorb moisture. When the dry air is passed through the wet cooling media of the cooler, the water molecules readily evaporate into the air, resulting in a greater cooling effect.

##### Q. How can water cool in a matka (earthen pot) throughout the summer?

Answer – Water kept in an earthen pot, also known as a matka, becomes cool during summer through a process called evaporative cooling.

The earthen pot is made of porous clay that allows air and water to pass through its walls. When water is stored in the pot, it seeps through the tiny pores and wets the surface of the pot. As the water evaporates from the surface of the pot due to the surrounding hot and dry air, it takes away heat from the water inside the pot, resulting in a cooling effect.

##### Q. Why does applying acetone, gasoline, or perfume to our palm make us feel cold?

Answer – Our palm feels cold when we put some acetone or petrol or perfume on it due to a process called evaporative cooling.

When a volatile liquid, such as acetone, petrol or perfume, is applied to the skin, it quickly evaporates into the surrounding air. During this process, the liquid takes away heat from the skin surface to overcome the intermolecular forces and enter the gaseous state. This transfer of heat from the skin surface to the evaporating liquid results in a cooling effect on the skin.

##### Q. Why can we drink hot tea or milk from a saucer more quickly than a cup?

Answer – Due to the increased surface area of the saucer, which speeds up the rate of heat transmission from the liquid to the surrounding air, it is possible to drink hot tea or milk more quickly from a saucer than from a cup.

##### Q. What kind of clothing is appropriate for summer?

Answer – In the summer, it’s crucial to dress in light, breathable clothing that will keep you cool and comfortable in the hot, muggy weather. Consider the following possibilities for clothing: garments with a loose fit, light-colored attire skirts and shorts, as well as breathable materials.

##### Q. The following temperatures should be converted to Celsius.(a) 293 K (b) 470 K.

Answer – To convert temperatures from the Kelvin (K) scale to the Celsius (°C) scale, we need to subtract 273.15 from the given temperature.

(a) 293 K = 293 – 273.15 = 19.85 °C

Therefore, 293 K is equivalent to 19.85 °C.

(b) 470 K = 470 – 273.15 = 196.85 °C

Therefore, 470 K is equivalent to 196.85 °C.

##### Q. The following temperatures should be converted to Kelvin scale.(a) 25°C (b) 373°C.

Answer – To convert temperatures from the Celsius (°C) scale to the Kelvin (K) scale, we need to add 273.15 to the given temperature.

(a) 25°C = 25 + 273.15 = 298.15 K

Therefore, 25°C is equivalent to 298.15 K.

(b) 373°C = 373 + 273.15 = 646.15 K

Therefore, 373°C is equivalent to 646.15 K.

##### Q. Give reason for the following observations.(a) Naphthalene balls vanish over time without leaving any solid.(b) We can get the smell of perfume from several metres away.

(a) Naphthalene balls disappear with time without leaving any solid because of a process called sublimation. Naphthalene balls are made of a solid chemical compound called naphthalene, which can change directly from a solid to a gas without going through the liquid phase. This means that when the naphthalene balls are exposed to air, they slowly undergo sublimation, turning from a solid directly into a gas without leaving any solid residue behind.

(b) We can get the smell of perfume sitting several metres away because perfume molecules are highly volatile, meaning they evaporate easily into the air. When we apply perfume to our skin or clothing, the perfume molecules begin to evaporate and spread out into the surrounding air. As these molecules travel through the air, they can be carried by air currents over a distance, which is why we can often smell perfume even if the person wearing it is several metres away. Additionally, our sense of smell is highly sensitive, so even a small amount of perfume molecules in the air can be detected by our noses.

##### Q. Arrange the following substances in ascending order of the forces of attraction between their particles—water, sugar, oxygen.

Answer – Oxygen —> water —> sugar.

##### Q. How does water physically behave at—(a) 25°C (bj 0°C (cj 100°C

Answer – The physical state of water at different temperatures is as follows:

(a) At 25°C, water is in a liquid state.

(b) At 0°C, water freezes and turns into a solid state, i.e., ice.

(c) At 100°C, water boils and turns into a gaseous state, i.e., steam or water vapor.

##### Q. Give two reasons to justify(a) water at room temperature is a liquid.(b) at room temperature, an iron almirah is solid.

(a) Two reasons to justify why water at room temperature is a liquid are:

1. At room temperature, the average kinetic energy of water molecules is not enough to break the intermolecular bonds between them completely, and they remain closely packed but in a mobile state. As a result, water molecules can flow and take the shape of the container they are placed in, making it a liquid.
2. The boiling point of water is 100°C and the freezing point of water is 0°C at standard atmospheric pressure. Since room temperature is typically around 25°C, it is well within the liquid phase range of water.

(b) Two reasons to justify why an iron almirah is a solid at room temperature are:

1. Iron atoms in the almirah are closely packed together due to strong interatomic forces, making it difficult for them to move freely. As a result, the almirah maintains its shape and does not flow or take the shape of the container it is placed in.
2. Iron has a high melting point of 1535°C and a high boiling point of 2750°C. At room temperature, which is typically around 25°C, the temperature is much lower than the melting point of iron, so the iron almirah remains in a solid state.
##### Q. Why does 273 K ice cool more efficiently than water does at the same temperature?

Answer – Ice at 273 K is more effective in cooling than water at the same temperature because of the difference in the heat capacity of ice and water. Heat capacity is defined as the amount of heat energy required to raise the temperature of a substance by 1 degree Celsius.

##### Q. What causes more severe boiling water, bums or steam?

Answer – More severe burns can result from steam than from boiling water.

This is due to the fact that steam contains a significant quantity of latent heat, or the energy needed to transform a gas into a liquid. Steam quickly loses heat and condenses into water droplets when it comes into contact with the skin. Large amounts of latent heat are released during this process, and this heat can transfer a lot of energy to the skin, leading to serious burns.

##### Q. Names A, B, C, D, E, and F in the picture below that depicts a change in status

Answer – A > Liquefication/melting/fusion B > Vapourisation/evaporation C >Condensation D > Solidification E > Sublimation F > Sublimation

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