This post contains Question Answer of chapter Matter in Our Surroundings including NCERT Exercise.
1. Which of these are matter: Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume?
Sol: The following are matter: chair, air, almonds, cold drink, smell of perfume.
2. Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Sol: This is because the particles of fragrance move faster at higher temperatures. In other words, the particles of fragrance diffuse faster at higher temperature.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Sol: This observation supports the following properties of water or liquids:
(a) The intermolecular forces in water are not very strong.
(b) The particles in liquids can be easily displaced from their original position.
(c) Liquids show reasonably high fluidity.
4. What are the characteristics of the particles of matter?
Sol: Characteristics of particle of matter are:
(a) Particles of matter are discrete.
(b) Particles of matter have space between them.
(c) Particles of matter are very small.
(d) Particles of matter consists of both kinetic and potential energy. The kinetic energy of particles increases with a rise in temperature.
(e) Particles of matter can intermix with others. During intermixing, the particles enter into the spaces in between.
5. The mass per unit volume of a substance is called density. Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Sol: The given substances are arranged in the order of increasing density as follows:
Air < Exhaust from chimneys < Cotton < Chalk < Water < Honey < Iron
6. (a) Tabulate the difference in the characteristics of the three states of matter.
(b) Comment upon the following – rigidity, compressibility, fluidity, filling of a gas in container, shape, kinetic energy and density.
Sol: (a) The difference in the characteristics of the three states of matter is:
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Rigidity | High | Low | Almost nil |
| Compressibility | Almost zero | Small | High |
| Shape and Volume | Definite shape and volume | No definite shape but definite volume | No definite shape and volume |
| Density | High | Somewhat lower than solids | Very low |
| Fluidity | Zero | Moderate | Very High |
| Intermolecular forces | Strong | Medium | Almost zero |
| Intermolecular space | Very less | Slightly more than solids | Very large |
| Diffusion | Zero | Moderate | Very high |
(b) Rigidity: Tendency to oppose any change in its shape is called rigidity. Solids are rigid.
Compressibility: Tendency to get squeezed under an applied force is called compressibility. Gases are highly compressible.
Fluidity: Tendency to flow is called fluidity. Gases and liquids have high fluidity.
Filling of a gas in a container: A gas when filled in a container occupies whole space.
Shape: Any sample of matter, takes up a shape depending upon the intermolecular forces and intermolecular volume. Liquids take the shape of the container, they are poured in. Gases have no shape but fill the container fully.
Kinetic energy: The energy by virtue by motion is called kinetic energy. In gases, the constituent particles move fast. So, gas molecules have very high kinetic energy.
Density: Mass per unit volume is called density. Solids and liquids have much higher density than gases.
7. Give reasons:
(a) A gas completely fills the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(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.
Sol: (a) In gases, the intermolecular forces are negligible. So, the particles of gases are free to move in any direction. As a result, gases fill the container in which they are kept.
(b) The particles in any gas move with high speeds in all directions. When these particles strike walls of the container, they exert force on them. Force per unit area is called as pressure.
So, gases exert pressure on the walls of the container due to the impact of the striking particles.
(c) The following properties suggest that a wooden table is a solid.
(i) It is rigid and incompressible.
(ii) It has definite shape and volume.
(iii) It has higher density.
(d) The intermolecular space in gases (air) is very large, whereas in solids (brick, block of wood) there is very little intermolecular space. In addition, the intermolecular forces in solids are very strong, whereas in gases, the intermolecular forces are negligible. Therefore, in gases (air), the constituent particles can be easily displaced.
8. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Sol: Ice has an open structure in which there is more intermolecular space. This reduces the density of ice as compared to that of water. That is why ice is lighter than water and floats on it.
9. Convert the following temperature to Celsius scale: (a) 300 K (b) 573 K.
Sol: (a) T = 300-273 = 27°C (b) T = 573-273 = 300°C
10. What is the physical state of water at: (a) 250°C (b) 100°C?
Sol: (a) Gas
(b) Both liquid and gas depending upon the conditions.
11. For any substance, why does the temperature remain constant during the change of state?
Sol: This is because, the heat supplied to the substance is used up during the change of state in overcoming the intermolecular forces.
12. Suggest a method to liquefy atmospheric gases.
Sol: Atmospheric gases can be liquefied by lowering temperature, by cooling, and increasing pressure.
13. Why does a desert cooler cool better on a hot dry day?
Sol: In a desert cooler, hot and dry air passes through wet pads of wood-shavings. Water takes heat from the hot air and evaporates. The evaporation of water cools the pads, and the circulating water. As a result, the incoming air also gets cooled down.
14. How does the water kept in an earthen pot become cool during summer?
So: An earthen pot has small pores in its walls. When water is poured into it, some of it seeps through these pores to its outer surface. On reaching there, it evaporates. The heat required for evaporation is taken from the earthen pot and from the water in it. As a result, the water in an earthen pot gets cooled down.
15. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Sol: Acetone, or petrol or perfume when placed on palm absorbs heat from the palm and evaporates. As a result, the palm fells cold.
16. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Sol: When hot tea or milk is taken in a saucer, it loses heat to the surroundings faster. This is due to large exposed surface area and hence we are able to sip it faster.
17. What type of clothes should we wear in summer?
Sol: During summers, we perspire more due to the body mechanism to keep it cool. Cotton is a good absorber of water. It absorbs the sweat and exposes it to the atmosphere. This speeds up evaporation of the sweat and causes cooling. This makes us feel comfortable.
18. Convert the following temperatures to the Celsius scale: (a) 293 K (b) 470 K.
Sol: (a) T = 293-273 = 20°C (b) T = 470-273 = 197°C
19. Convert the following temperatures to the Kelvin scale: (a) 25°C (b) 373 °C.
Sol: (a) T = 25+273 = 298 K (b) T = 373+273 = 646 K
20. Give reason for the following observation:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several meters away.
Sol: (a) Naphthalene sublimes even at room temperature. The vapour of naphthalene either gets absorbed by the fabric or escapes into the atmosphere.
(b) The particles of perfume diffuse into the air to reach persons sitting a few meters away.
21. Arrange the following substances in the increasing order of force of attraction between the particles: Water, Sugar and Oxygen.
Sol: The arrangement in the increasing order of intermolecular forces is:
Oxygen < Water < Sugar
22. What is the physical state of water at: (a) 25°C (b) 0°C (c) 100°C.
Sol: (a) Liquid
(b) Solid in equilibrium with liquid or only solid depending upon the conditions.
(c) Water vapour in equilibrium with liquid water or only water vapour depending upon the conditions.
23. Give two reasons to justify:
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.
Sol: (a) Water at room temperature is a liquid because:
(i) In water, the intermolecular forces are strong enough to keep its particle bound to each other.
(ii) The melting point of water is below room temperature
(b) An iron almirah is a solid at room temperature because:
(i) It has a fixed shape and definite volume.
(ii) It is rigid and cannot be deformed easily. This shows that the intermolecular force in iron are very strong.
24. Name A, B, C, D, E and F in the following diagram showing change in its state.
Sol: A: Fusion or Melting
B: Vaporisation or Boiling
C: Condensation
D: Solidification or Freezing
E: Sublimation
F: Desublimation or Vapour deposition
25. Why is ice at 273 k more effective in cooling than water at the same temperature?
Sol: Ice at 273 kelvin is more effective in cooling than water at the same temperature because it can draw from any other body, 3.35*105 J/Kg heat (equal to its latent heat of fusion) more than the same mass of water at the same temperature.
26. What produces more severe burns, boiling water or steam?
Sol: Steam produces more severe burns than boiling water because it can release 22.6*105 J/Kg of heat more than the same quantity of boiling water (due to its latent heat of vaporisation).
27. Name the state of matter in which-
(a) Layers of particles can slip and slide over each other.
(b) Particles just move around randomly because of very weak force of attraction.
Sol: (a) Liquid (b) Gas
28. Osmosis is a special kind of diffusion. Comment.
Sol: In diffusion, two or more gases in intermix directly whereas during osmosis the solvent molecules migrate from solvent to the solution side through a semipermeable membrane.
29. The pistons of two syringes – one filled with air and other with water are pushed inwards with equal force. What will you observe? What can be concluded from this activity?
Sol: The piston of the syringe containing air can be easily pushed inwards because air is compressible.
The piston of the syringe containing water cannot be pushed inwards because water is almost incompressible.
30. In an experimental setup for sublimation, a perforated asbestos sheet is placed between the china dish and funnel. What is the purpose of it?
Sol: The asbestos sheet prevent direct heating of the funnel. The holes in the asbestos sheet permit the vapour of the sublime to enter the inverted funnel.
31. A strong smelling gas is stored in cylinders as liquid but it comes out of the cylinder as gas.
(a) Name the gas.
(b) What causes this change in state?
(c) Name the process of this conversion.
Sol: (a) LPG (Liquefied Petroleum Gas).
(b) LPG gets converted into gas due to lowering of pressure.
(c) Vaporisation
32. The boiling point of water is much higher than that of petroleum ether. In which of the two, the intermolecular forces are strong?
Sol:The intermolecular forces are stronger in water.
33. A sample of water under study was found to boil at 102°C at normal pressure.
(a) Is the water pure?
(b) Will this water freeze at 0°C? Comment.
Sol: (a) The given sample of water is not pure.
(b) The given sample of water will not freeze at 0°C. The impurities which will raise boiling point lower the freezing point of water. Hence, the given sample of the water will freeze at below 0°C.
34. (a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion. What is meant by latent heat of fusion?
Sol: (a) The term used to denote the conversion of vapour to solid is called vapour deposition or desublimation.
(b) The quantity of heat required to convert 1 unit mass of ice into liquid water at 0°C, under normal pressure, is called the latent heat of fusion of ice.
35. Water as ice has a cooling effect whereas water as steam may cause severe burns. Explain.
Sol: Ice absorb heat from the body to melt. That’s why, it gives cooling effect. When steam comes in contact with our body, it condenses and give out a large amount of heat. This heat causes burns.
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