Physical & Chemical Changes | Is Matter Around us Pure?

uestions Both water and cooking oil are liquid but their chemical characteristics are different. 1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25ºC), which are They differ in odour and inflammability. We know that oil burns in air whereas water extinguishes fire. It is this chemical property of oil that makes it different from water. Burning is a chemical change. During this process one substance reacts with another to undergo a change in chemical composition. Chemical change brings change in the chemical properties of matter and we get new substances. A chemical change is also called a chemical reaction. miscible with each other? 2. Name the technique to separate (i) butter from curd, (ii) salt from sea-water, (iii) camphor from salt. 3. What type of mixtures are separated by the technique of crystallisation? During burning of a candle, both physical and chemical changes take place. Can you distinguish these? 2.4 Physical and Chemical Changes uestions To understand the difference between a pure substance and a mixture, let us understand the difference between a physical and a chemical change. In the previous chapter, we have learnt about a few physical properties of matter. The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properites. The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance. 1. Classify the following as chemical or physical changes: cutting of trees, melting of butter in a pan, rusting of almirah, boiling of water to form steam, passing of electric current, through water and the water breaking down into hydrogen and oxygen gases, dissolving common salt in water, making a fruit salad with raw fruits, and • burning of paper and w0od. Although ice, water and water vapour all look different and display different physical properties, they are chemically the same. 2. Try segregating the things around you as pure substances or mixtures.