Tiêu đề CHEM 9th.pdf ✅

EVOKE For class 9TH study material CHEMISTRY Key Features Detailed Theory with NCERT Intext Questions | Mind it, Find it and Test Prep Sections | Quick Recall | NCERT Exercises | Subjective Questions | MCQs | Assertion & Reason | Case Based Questions with Explanation
Chapter-1 Matter in our Surroundings ( 5 ) Chapter-2 Is Matter Around Us Pure? ( 39 ) Chapter-3 Atoms and Molecules ( 81 ) Chapter-4 Structure of the Atom ( 123 ) Contents
CHAPTER MATTER IN OUR SURROUNDINGS 1 Introduction In our surrounding, there are a lot of things that we may see and feel all around us. All these things differ in their shapes, sizes and textures. Let’s take the example of a table. We can feel the weight of the table if we pick it up, hence it may be concluded that the table has some mass, also it occupies some space, and the space occupied by the table is known as its volume. We cannot see the air around us, but if we carefully weigh the balloon filled with air, we will find that along with occupying space (bounded by the balloon), it also has mass. Hence, Matter can be defined as “Anything that occupies space and has mass”. Example: Table, chair, water, food, air, trees etc. The matter is classified on the basis of their physical and chemical properties: Physical Nature of Matter I. Particulate Nature of Matter–Matter is Made Up of Particles For a long time, there were two views about matter, i.e. whether it is continuous like a sheet of glass or particulate in nature like sand. To decode the nature of matter, hold a sheet of glass in your hands. It appears continuous. Now, throw it on the floor, it breaks into tiny particles. This proves that matter is not continuous but is particulate in nature, i.e. made of tiny particles. II. Particles of Matter are Tiny in Size U Take 2-3 crystals of potassium permanganate and dissolve them in 100 mL of water taken in a beaker. The colour of the solution will be purple. U Transfer 10 mL of this solution into another beaker containing 90 mL of clear water. U The intensity of the purple colour decreases. Keep diluting the solution like this 5 to 8 times. Observation: It is surprising to note that even after multiple dilutions the colour becomes lighter and lighter but doesn’t disappear. Conclusion: There must be millions of tiny particles in one crystal of potassium permanganate which keeps on dividing with each dilution. "All matter originates and exists only by virtue of a force which brings the particle of an atom to vibration and holds this most minute solar system of the atom together" (Max Planck) K I C K O F F
6 Evoke Study Material Class-IX 10 ml 10 ml 100 ml 100 ml 100 ml 100 ml 100 ml Fig. 1: Estimating how small are the particles of matter. With every dilution, though the colour becomes light, it is still visible Characteristics of Particles of Matter I. Particles of Matter have Spaces Between Them The particles of matter have spaces between them. For example-When we make lemonade, tea or coffee, particles of one type of matter get into the spaces between particles of the other which shows that there is enough space between particles of matter. II. Particles of Matter are Continuously Moving Are particles of matter stationary or continuously moving? To answer this question, let us carry out the below experiment. U Place an unlit incense stick in a corner of the room. You will have to go close to the incense stick to get its smell. U Now, light the incense stick and sit at a distance to the incense stick. Observation: You will get the smell of the incense stick while sitting at a distance from the stick. Reason: As the temperature of the incense stick increases, the kinetic energy (energy associated with the motion of particles) increases and the particles of the incense stick mix rapidly with the particles of air. Similarly, when the incense stick was not lit, the temperature was low and hence the kinetic energy of the particles of incense stick was low. Conclusion: Particles of matter are continuously moving, i.e. they possess kinetic energy. As the temperature rises, the kinetic energy of the particles also increases. In the above experiment, we observe that the particles of matter intermix on their own to achieve uniform composition and this is known as diffusion. Mind it The aquatic plants and animals survive because the gases from the atmosphere diffuse and dissolve in water. These gases mainly contain carbon dioxide and oxygen. These are taken by the animals and plants for their survival. Example 1. The purple color of potassium permanganate spreads through out the water when a crystal of potassium permanganate is dropped into a beaker containing water. What can be concluded from this observation about the nature of potassium permanganate and water? Ans. As soon as a crystal of potassium permanganate is dissolved in water, the particles of potassium permanganate diffuse in between the particles of water to form a homogeneous (uniform composition) solution. This is an example of diffusion of solid into liquid diffusion. Fig. 2: Smell of incense stick reach to us by the process of diffusion