Active Chemistry Past Paper PDF

"Water changes to crystals Baking oftoast Boiling eggs Cracking eggs of varlous shapes a...

"Water changes to crystals Baking oftoast Boiling eggs Cracking eggs of varlous shapes and sizes depen ding on the temperature," bread Lighting a matchstick Roasting food Slicing 2H,0, 2H,O + O, Hydrogen Water Oxygen peroxide Physical change of Chemical change of hydrogen water into ice peroxide into water 1. Introduction We know that nothing on this Earth ever really disappears. may be seen It like snow disappears in the Sun or the flames that wood makes vanish in a but that is not what is happening. Snow melts and becomes liquid fire, and which on evaporation tums into gas that rises into the atmosphere smoke. bunt wood turns into ash and Matter can never be created or destroyed. just changes its form. It All matter is made up of tiny molecules and when these molecules are changed or moved around, the matter changes its form. Everyday, you experience changes inmatter. Cooking eggs, burning leaves, freezing water and mixing oil and vinegar to make salad dressing, involve changes in matter. We classify these changes into two categories 0 Physical changes Heat Haat (G) Chemical changes Understanding and categorising these changes is an important step in lcels) Watert) Steamlg) leaming how to use them. Coo Cool 2. Physical changes Fig.1 Conversion of water in three AcTIVE CHEMISTRY 1 states is a physical change. Aim To show some physical changes. Materials required Sheet of paper, scissors,ice cubes,glass tumbler, table lamp, boiling water and pan.  Procedure c ) Cut paper into foursquare pleces. Cut one the sheet of In a physical om foursquare pieces. Lay these pieces on the table so that square farther apart the kind o acquire the shape of the original piece of paper. pleces no new (G) Take some ice cubes in a glasstumbler and melt a small For example, by placing the tumbler in the Sun.You have now portion of a mixture () When wa of Now place the tumbler in the freezing chamber iceand change c water. of for a few hours. your we fridoe () When Watch the bulb of your table lamp carefully. Watch motion. (ii) the becoming white hot and emitting light when you switch on (larmen the (i) A sheet Suitch it off and observe. lamp flattens (iv) Take some boiling water and place an inverted pan over and observe. the CONC steam at some distance rising BUILDING Observation Dissolving s () The pieces of paper be joined back to makethe carnnot original Explanatio the property of the paper remains the same. but Dissolving is The melted ice forms water and water freezes back toform ice. (ii) spr particles (G) The bulb is back to its original state and does not give light. You can reve (iv) Some water droplets are found to condense onthe inner surface o ch Physical the pan. or a chang Conclusion shape and Reversibl () The paper undergoes a change in size. (Gi) lce undergoes a change in state. Changes th are often (Gi) Bulb undergoes a change in colour and steam undergoes changein that occur state. all the above cases, no new substance is formed and all You cannc In changes are THE reversible and temporary. Hence, all of them undergo a physical chano pieces. CE SPOT Properties such as shape, size, colour and state of a substance are cal 3. Chemic LIGHT its physical properties. A change in which a substance undergoes a chano CHE A hemical hange ocCurs when two in its physical properties is called a physical change. A physical change ACTIVE hemical substances interadto produce generally reversible. In such a change, no new substarnce is formed. Aim new substance (or substances) with a Characteristicfeatures of physical changes To show different set of properties. (1) The identity of the substance is maintained. Materia (2) The change is temporary. Iron nailL (3) Heat change may or may not take place. fresh m (4) Only the physical state or some of the physical properties of the Proced substances are changed. Moister In a physical change, the substance that is involved remains the sanme your h even though its form or state may change. A piece of wood when cut into Obser pieces,is still a wood.When ice melts, same substance.Changes it is stillthe () Iro of state-melting, freezing, evaporation,condensation and sublimation, are fro physical changes. Somemore examples of physical changes are (6) T () Mixing salt and water. (ii) C () The falingof any objectunder gravity. (v) T (ii) Vase breaks into pieces. Conc (iv) Ink being absorbed by a blotting paper or chalk. Can y () Stretching of a rubber band. state (vi) Grinding a fruit to pulp in a mixer. form (vii) Dew drops condensing on a leaf at dawn. colou (vii) Copper metal being drawn into wires.  colour, change. chemical called a a Such smell is change taste, or substances ireversible changes their may the and are The change fomed. change. substance composition substances New well are the of as state changes? reverse changes, possible. Obviously, these as you Can these In is it all not Conclusion smell. curdles and The sour milk gives (iv) discoloured vegetable Cooked and dal gets foul or (iüi) a smell. and potato gets The (i) foul gives black almost gives smell. a iron. from different substance reddish covered with