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Class 9 Science NCERT Exemplar Solutions for Chapter 1 - Matter in Our Surroundings include the simplest answers and explanations to all the questions. All the class 9 students would find these answers really easy which would help them clear the concepts and perform well in their Class 9 Science Exam. Get a PDF copy of all questions and answers to refer to at your convenience.
1.Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases
Answer: c) Evaporation, diffusion and expansion of gases
Increase in temperature increases the kinetic energy possessed by the particles of matter. All three phenomenon evaporation, diffusion and expansion of gases involve movement of particles away from each other. Therefore, the rate of evaporation, diffusion and expansion of gases increases on raising the temperature.
2.Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
Answer: c) Low temperature, high pressure
To compress a gas into liquid, low temperature and high pressure are required. These conditions would make the gas particles come closer and they start attracting each other to form a liquid.
3.The property to flow is unique to fluids. Which one of the following statements is correct?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids
Answer: c) Gases and liquids behave like fluids
Gases and liquids possess lower intermolecular force of attraction which facilitates flow of these states of matter.
4.During summer, water kept in an earthen pot becomes cool because of the phenomenon of
Evaporation of water through pores of earthen pot reduces temperature of immediate surroundings. This makes the water cool after some time.
5.A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?
Answer: c) Oxygen, water, sugar
The intermolecular force of attraction increases in the order - Gas < Liquid < Solid.
6.On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K
Answer is a) 298 K, 311 K and 339 K
Temp in Kelvin = Temp in Celsius + 273
7.Choose the correct statement of the following
(a) Conversion of solid into vapours without passing through the liquid state is called sublimation.
(b) Conversion of vapours into solid without passing through the liquid state is called vaporisation.
(c) Conversion of vapours into solid without passing through the liquid state is called freezing.
(d) Conversion of solid into liquid is called sublimation.
Answer : a) Conversion of solid into vapours without passing through the liquid state is called sublimation.
Sublimation is a process in which a solid is converted into vapours without passing through a liquid state.
8.The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale?
Answer: c) 308 K, 329 K, 391 K
Temp in Kelvin = Temp in Celsius + 273
9.Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water
Answer: a) Increase in temperature of water
Rate of evaporation increases with increase in temperature due to the increased kinetic energy of water molecules on raising temperature.
10.In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas
(iv) Adding more hydrogen gas to the container without increasing the volume of the container
Answer: c) ii and iii
To increase the intermolecular distance between the molecules of hydrogen gas either volume of Hydrogen gas in container should be reduced or the volume of the container should be increased.
11.A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.
No, the sample of water given here is not pure because the boiling point of pure water is 100°C and the melting point is 0°C at 1 atmospheric pressure. Since the given water is not pure therefore it will freeze at a temperature below 0°C.
12.A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following (Fig. 1.1) would correctly represent the result? Justify your choice.
Figure (d) would correctly represent the result because at the start of the experiment temperature of the mixture would be zero as water and ice will be in equilibrium. When the student starts heating the mixture initially latent heat will be utilised to melt the ice.S Hence the temperature would remain constant for a certain period of time. When the mixture is heated further the temperature of the water increases gradually.
(a) Evaporation of a liquid at room temperature leads to __________effect.
(b) At room temperature the forces of attraction between the particles of solid substances are___________than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the___________ state. However, there is no order in the ___________ state.
(d)___________ is the change of solid state directly to vapour state without going through the ___________state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called___________.
14.Match the physical quantities given in column A to their S I units given in column B:
(v) kilogram per cubic metre
(c) Density (v) kilogram per cubic metre
(e) Volume (i) cubic metre
15.The non-SI and SI units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity:
(c) Gram per centimetre cube
(v) kilogram per metre cube
(a) Degree Celsius (iv) kelvin
(c) Gram per centimetre cube (v) kilogram per metre cube
(d) Bar (ii) pascal
16.‘Osmosis is a special kind of diffusion’. Comment.
Diffusion is a process in which particles of liquids and gases move from high concentration to low concentration. Whereas, osmosis is the movement of particles from the low concentration to high concentration through a semi-permeable membrane. Hence, osmosis is termed as a special kind of diffusion.
17.Classify the following into osmosis/diffusion
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked throughout the house.
(g) Aquatic animals using oxygen dissolved in water during respiration
18.Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.
Water as ice has low energy as it freezes at 0o C. When it comes in contact with our skin it draws heat of the body giving it a cooling effect. On the other hand, steam has more latent heat stored in it as compared to water as solid and liquid. Hence, due to its high energy it causes severe burns.
19.Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.
Temperature of steam and water boiling in the kettle is the same which is 100o C. But the particles of steam have more energy in the form of latent heat of vaporisation than the particles of water. Due to this, steam is hotter than boiling water.
20.A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.
Graph (a) correctly represents the change in the temperature of water as a function of time. At first, water will cool down until its temperature reaches 0 °C. After reaching the freezing point (0 °C) temperature will remain constant until the water becomes ice. On further cooling, the temperature of ice will slowly fall down with time.
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