Save a small sample of the solution in a test tube or a small glass bottle. Add a few drops of dilute sulphuric acid to the solution. Activity 7 (To be demonstrated by the teacher)ĭissolve about a teaspoonful of copper sulphate (blue vitriol or neela thotha) in about half a cup of water in a glass tumbler or a beaker. Magnesium hydroxide is another new substance formed by mixing magnesium oxide with water. So, magnesium oxide is a new substance formed on burning of magnesium. Magnesium oxide (MgO) + Water (H 2O) → Magnesium hydroxide Īs you have already learnt in Chapter 5, magnesium hydroxide is a base. This change can be written in the form of the following equation: On dissolving the ash in water it forms a new substance. On the basis of this test, how do you classify the aqueous solution - acidic or basic? Test the mixture with blue and red litmus papers. Stir the mixture (aqueous solution) well. To balance chemical equations at this stage.Ĭollect the ash and mix it with a small amount of water. In equations of this kind, the arrow implies ‘becomes’. The equations here are different from those in mathematics. It is different from iron on which it gets deposited. In the kitchen, a wet iron pan (tawa) often gets rusted if left in that state for some time.Rust is not iron. At home you must have seen shovels and spades getting rusted when exposed to the atmosphere for some time. Iron gates of parks or farmlands, iron benches kept in lawns and gardens, almost every article of iron, kept in the open gets rusted. This substance is called rust and the process is called rusting (Fig. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. CHEMICAL CHANGEĪ change with which you are quite familiar is the rusting of iron. Let us now consider the other kind of change. In such a change no new substance is formed. A physical change is generally reversible. A change in which a substance undergoes a change in its physical properties is called a physical change. Properties such as shape, size, colour and state of a substance are called its physical properties. In Activity 5, the hack-saw blade changed colour on heating. In Activities 3 and 4, water changed its state (from solid to liquid, or from gas to liquid). Observe the tip once again after some time.ĭoes it get back its original colour? In Activities 1 and 2 above, you saw that paper and a piece of chalk underwent changes in size. Wait for a few minutes.ĭoes the colour of the tip of the blade change? Keep the tip of the free end on the flame of a gas stove. Hold a used hack-saw blade with a pair of tongs. Observe the inner surface of the pan.ĭo you see any droplet of water there? Activity 5ĬAUTION : Be careful while handling a flame. Do you see the steam rising from the surface of water? Hold an inverted pan by its handle over the steam at some distance from the boiling water. Now place the tumbler in a freezing mixture (ice plus common salt).ĭoes the water become solid ice once again? Activity 4īoil some water in a container. Melt a small portion of ice by placing the tumbler in the sun. Take some ice in a glass or plastic tumbler. Let it dry.ĭid you recover chalk from the dust? Activity 3 Roll it into the shape of a piece of chalk. Add a little water to the dust to make a paste. Or, crush a small piece of chalk into dust. Obviously, you cannot join the pieces back to make the original piece, but is there a change in the property of the paper? Activity 2Ĭollect the chalk dust lying on the floor near the blackboard in your classroom. Lay these pieces on the floor or a table so that the pieces acquire the shape of the original piece of paper (Fig. Cut each square piece further into four square pieces. PHYSICAL CHANGES Activity 1Ĭut a piece of paper in four square pieces.
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