Matter in Our Surroundings

This chapter explains that everything around us is made of matter, which occupies space and has mass, and that matter is made of tiny particles. Simple activities such as dissolving salt in water, diluting potassium permanganate and smelling incense from a distance show that particles have spaces between them, are continuously moving and attract each other. You will compare the three states of matter, solid, liquid and gas, in terms of shape, volume, compressibility, rigidity, fluidity and diffusion, and see why gases are highly compressible, allowing LPG and CNG to be stored in cylinders. You will study how matter changes its state with temperature and pressure: the melting point of ice is 273.15 K, the boiling point of water is 373 K, and the hidden energy absorbed during a change of state is called latent heat of fusion or vaporisation. You will learn about sublimation, as in camphor, and the Kelvin scale, where K = degrees Celsius + 273. Finally, you will learn how surface area, temperature, humidity and wind speed affect evaporation and why evaporation causes cooling.

Detailed Worksheet: Matter in Our Surroundings Section A - Definitions (10 marks) 1. What is matter? Give two characteristics of the particles of matter. (2 marks) 2. What is diffusion? Why is it fastest in gases? (2 marks) 3. Define melting point and boiling point. Give the values for ice and water in kelvin. (2 marks) 4. What is latent heat? Distinguish between latent heat of fusion and latent heat of vaporisation. (2 marks) 5. What is sublimation? Give two examples of substances that sublime. (2 marks) Section B - Calculations and Applications (15 marks) 6. Convert the following temperatures to the Celsius scale: 300 K, 573 K. Convert to the Kelvin scale: 25 degrees Celsius, 373 degrees Celsius. (3 marks) 7. The density of a substance is mass per unit volume. A block of mass 540 g has a volume of 200 cubic cm. Find its density. Will it float or sink in water of density 1 g per cubic cm? (3 marks) 8. Arrange the following in increasing order of the forces of attraction between their particles: water, sugar, oxygen. Give a reason. Also arrange them in increasing order of density: air, exhaust from a chimney, honey, water, chalk, cotton, iron. (3 marks) 9. A substance melts at 80 degrees Celsius and boils at 218 degrees Celsius. What is its physical state at (i) 25 degrees Celsius (ii) 100 degrees Celsius (iii) 250 degrees Celsius? Convert its melting and boiling points to kelvin. (3 marks) 10. Two identical wet clothes are dried, one on a sunny windy day and the other on a humid still day. Which dries faster? Explain using four factors that affect evaporation. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the experiment to show the change of ice into water and then into steam, with a thermometer, beaker and burner. Draw the temperature-time graph and mark the regions where latent heat is absorbed. (4 marks) 12. Draw a labelled diagram of the sublimation of camphor or ammonium chloride using a china dish, inverted funnel and cotton plug. (3 marks) 13. Draw diagrams showing the arrangement of particles in a solid, a liquid and a gas. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain, giving reasons: (i) a gas fills completely the vessel in which it is kept (ii) a gas exerts pressure on the walls of the container (iii) a wooden table should be called a solid (iv) we can easily move our hand in air but not through a solid block of wood. (5 marks) 15. Explain why: (i) we sweat more on a humid day (ii) water kept in an earthen pot becomes cool in summer (iii) our palm feels cold when we put acetone or perfume on it (iv) we are able to sip hot tea or milk faster from a saucer than a cup (v) we should wear cotton clothes in summer. (5 marks) 16. Explain the effect of pressure and temperature on changing gases into liquids. Why is solid carbon dioxide called dry ice? Why is steam at 100 degrees Celsius more harmful than boiling water at the same temperature? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Use K = degrees Celsius + 273 for conversions unless told otherwise.