matter in our surroindings 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 Soln: Answer is c) Evaporation, diffusion and expansion of gases Explanation: Particles of matter are continuously moving as they possess kinetic energy. When temperature is raised particles of matter intermix with each other which is called diffusion. Evaporation means conversion of liquid state into vapour state. When we increase temperature molecules move and vibrate so quickly that they escape into the atmosphere in the form of vapours. Increase in temperature causes the molecules to move faster, which results in expansion of gases. 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 Soln: Answer is c) Low temperature, high pressure Explanation: To compress gas into liquid, low temperature and high pressure are required. Between the particles of gas there is a lot of space. On applying pressure, particles get closer and they start attracting each other to form a liquid. A lot of heat is generated when gas is compresses hence it is necessary to cool it. Cooling lowers the temperature of compressed gas and helps in liquefying it. 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 Soln: Answer is c) Gases and liquids behave like fluids Explanation: In gases and liquids intermolecular force of attraction between the particles is less and they facilitate flow of these states of matter. 4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of (a) diffusion (b) transpiration (c) osmosis (d) evaporation Soln: Answer is d) evaporation Explanation: Evaporation of water through pores of earthen pot reduces temperature of immediate surroundings. This makes the water cool after some time. Movement of water through plants and evaporation through its aerial parts is called transpiration. Diffusion is the movement of a substance from an area of higher concentration to an area of lower concentration If molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, it is called osmosis. 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? (a) Water, air, wind (b) Air, sugar, oil (c) Oxygen, water, sugar (d) Salt, juice, air Soln: Answer is c) Oxygen, water, sugar Explanation: The intermolecular force of attraction is less in gases than liquid and solid. Solids have higher intermolecular attraction compared to liquid. In the answer, oxygen is a gas which has lesser intermolecular attraction than water-a liquid and sugar- a crystalline 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 Soln: Answer is a) 298 K, 311 K and 339 K Explanation: Add 273 to respective temperature to get the temperature in kelvin. 25°-298K, 38°-311K, 66°-339K 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. Soln: Answer is a) Conversion of solid into vapours without passing through the liquid state is called sublimation. Explanation: Sublimation is a process in which a solid is converted into vapours without passing through a liquid state. Vaporisation is a phase transition from liquid to vapours. Conversion of liquid to solid at substance’s freezing temperature is called as freezing. 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? (a) 306 K, 329 K, 391 K (b) 308 K, 329 K, 392 K (c) 308 K, 329 K, 391 K (d) 329 K, 392 K, 308 K Soln: Answer is c) 308 K, 329 K, 391 K Explanation: The temperature in Celsius can be converted into temperature in kelvin by adding 273 to the Celsius value. Boiling points of diethyl ether, acetone and n-butyl alcohol are 308 K, 329 K, and 391 K, respectively. 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 Soln: Answer is a) Increase in temperature of water Explanation: Increase in temperature of water increases the kinetic energy of the water which will make more particles to attain enough energy to convert into the vapour state. This is how an increase in temperature favours evaporation. On the other hand, the exposed surface is also responsible for the evaporation. Higher the exposed surface, higher will be the evaporation. When common salt is added to water then the surface is occupied by the solvent as well as non-volatile solute particles. This makes the escaping tendency of solvent particles decrease and thus the evaporation of water decreases. Hence options (b), (c) and (d) will decrease the evaporation of water. 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 (a) (i) and (iii) (b) (i) and (iv) (c) (ii) and (iii) (d) (ii) and (iv) Soln: Answer is c) ii and iii Explanation To increase the intermolecular interaction either volume of Hydrogen gas should be reduced or container volume should be increase. By increasing the pressure or by adding Hydrogen without increasing container volume inter-molecular interaction would decrease. Water under study was found to boil at 102°C at normal temperature and pressure. Short Answer Questions 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. Soln: The boiling point of pure water is 100 °C and the melting point is 0°C at 1 atmospheric pressure. Here the water boils at 102 °C hence it is not pure water and freezes 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. Soln: Answer is d) because at the start of the experiment temperature of the mixture would be zero as water and ice will be in equilibrium. When students start heating initially latent heat will be utilised to melt the ice. Hence the temperature did not increase for a certain amount of time. When students heat the mixture further the temperature of the water increases gradually. 13. Fill in the blanks: (a) Evaporation of a liquid at room temperature leads to a——— 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———. Soln: Cooling Stronger Liquid, gaseous Sublimation, liquid Evaporation 14. Match the physical quantities given in column A to their S I units given in column B: (A) (B) (a) Pressure (i) cubic metre (b) Temperature (ii) kilogram (c) Density (iii) pascal <