6 Changes Physical And Chemical Prashanth Ellina-Books Pdf

6 Changes Physical and Chemical Prashanth Ellina
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Activity 6 4 6 3 and 6 4 water changed its state from. solid to liquid or from gas to liquid In, Boil some water in a container Do you. Activity 6 5 the hack saw blade, see the steam rising from the surface of. changed colour on heating, water Hold an inverted pan by its. Properties such as shape size colour, handle over the steam at some distance. and state of a substance are called its, from the boiling water Observe the.
physical properties, properties A change in which, inner surface of the pan. a substance undergoes a change in its, Do you see any droplet of water. physical properties is called a physical, change A physical change is generally. Activity 6 5 reversible In such a change no new, CAUTION substance is formed. Let us now consider the other kind, Be careful while handling a flame.
Hold a used hack saw blade with a, pair of tongs Keep the tip of the free 6 2 CHEMICAL CHANGE. end on the flame of a gas stove Wait for A change with which you are quite. a few minutes familiar is the rusting of iron If you. Does the colour of the tip of the blade leave a piece of iron in the open for some. change time it acquires a film of brownish, Remove the blade from the flame substance This substance is called rust. Observe the tip once again after some and the process is called rusting. time Fig 6 2 Iron gates of parks or, Does it get back its original colour farmlands iron benches kept in lawns. In Activities 6 1 and 6 2 above you and gardens almost every article of iron. saw that paper and a piece of chalk kept in the open gets rusted At home. underwent changes in size In Activities you must have seen shovels and spades. getting rusted when exposed to the, Fig 6 2 Rusting iron. PHYSICAL AND CHEMICAL CHANGES 59, atmosphere for some time In the light Fig 6 3 When it is completely.
kitchen a wet iron pan tawa often gets burnt it leaves behind a powdery ash. rusted if left in that state for some time Does the ash look like the. Rust is not iron It is different from iron magnesium ribbon. on which it gets deposited The change can be represented by. Let us consider a few more changes the following equation. where new substances are formed Magnesium Mg Oxygen O2. Magnesium oxide MgO, Activity 6 6, To be demonstrated by the teacher. The equations here are different from, those in mathematics In equations. It is dangerous to look for long at the of this kind the arrow implies. burning magnesium ribbon The becomes No attempt should be made. teachers should advise children not to balance chemical equations at this. to stare at the burning ribbon stage, Get a small piece of a thin strip or. Collect the ash and mix it with a, ribbon of magnesium Clean its tip with. small amount of water Stir the mixture, sandpaper Bring the tip near a candle.
aqueous solution well Test the mixture, flame It burns with a brilliant white. with blue and red litmus papers, Does the mixture turn red litmus. Does the mixture turn blue litmus, On the basis of this test how do you. classify the aqueous solution acidic, On dissolving the ash in water it. forms a new substance This change can, be written in the form of the following.
Magnesium oxide MgO Water, H2O Magnesium hydroxide Mg OH 2. As you have already learnt in, Chapter 5 magnesium hydroxide is a base. So magnesium oxide is a new substance, formed on burning of magnesium. Fig 6 3 Magnesium ribbon burning Magnesium hydroxide is another new. 60 SCIENCE, substance formed by mixing magnesium colour of the solution from blue to. oxide with water green is due to the formation of iron. sulphate a new substance The brown, Activity 6 7, deposit on the iron nail is copper.
To be demonstrated by the teacher another new substance We can write. Dissolve about a teaspoonful of copper the reaction as. sulphate blue vitriol or neela thotha in Copper Sulphate solution blue Iron. about half a cup of water in a glass Iron Sulphate solution green. tumbler or a beaker Add a few drops of Copper brown deposit. dilute sulphuric acid to the solution, You should get a blue coloured solution. Activity 6 8, Save a small sample of the solution in a Take about a teaspoonful of vinegar in. test tube or a small glass bottle Drop a a test tube Add a pinch of baking soda. nail or a used shaving blade into the to it You would hear a hissing sound. remaining solution Wait for half an and see bubbles of a gas coming out. hour or so Observe the colour of the Pass this gas through freshly prepared. solution Compare it with the colour of lime water as shown in Fig 6 5. the sample solution saved separately What happens to the lime water. Fig 6 4 Change in colour of the copper sulphate, solution due to reaction with iron. Do you see any change in the colour The change in the test tube is as. of the solution follows, Take out the nail or the blade Vinegar Acetic acid Baking soda. Has it changed in any way Sodium hydrogencarbonate. The changes that you notice are Carbon dioxide other substances. due to a reaction between copper The reaction between carbon dioxide. sulphate and iron The change of and lime water is as follows. PHYSICAL AND CHEMICAL CHANGES 61, A change in which one or more.
new substances are formed is called a, chemical change. change A chemical change, is also called a chemical reaction. dioxide Chemical changes are very important, in our lives All new substances are. formed as a result of chemical changes, Baking soda. For example if a metal is to be extracted, from an ore such as iron from iron ore.
Lime we need to carry out a series of chemical, water changes A medicine is the end product. of a chain of chemical reactions Useful, new materials such as plastics and. Fig 6 5 Set up to pass gas through lime water, detergents are produced by chemical. reactions Indeed every new material, Carbon dioxide CO2 Lime water. is discovered by studying chemical, Ca OH 2 Calcium Carbonate.
CaCO3 Water H2O, We have seen that one or more new. When carbon dioxide is passed, substances are produce in a chemical. through lime water calcium carbonate, change In addition to new products. is formed which makes lime water milky, the following may accompany a chemical. The turning of lime water into milky is a, standard test of carbon dioxide You will.
Heat light or any other radiation, use it in Chapter 10 to show that the air. ultraviolet for example may be given, we breathe out is rich in carbon dioxide. off or absorbed, In Activities 6 6 6 8 you saw that. Sound may be produced, in each change one or more new. A change in smell may take place or, substances were formed In Activity 6 6.
the ash was the new substance formed a new smell may be given off. when magnesium was burnt In Activity 6 7 A colour change may take place. the reaction of copper sulphate with iron A gas may be formed. produced iron sulphate and copper Let us look at some examples. Both of these are new substances You saw that burning of magnesium. Copper was deposited on the shaving ribbon is a chemical change Burning. blade of iron In Activity 6 8 vinegar and of coal wood or leaves is also a chemical. baking soda together produced carbon change In fact burning of any. dioxide which turned lime water milky substance is a chemical change. Can you name the new substance Burning is always accompanied by. formed in this reaction production of heat, 62 SCIENCE. Explosion of a firework is a chemical, change You know that such an. explosion produces heat light sound, We learnt in Chapter 1 that. and unpleasant gases that pollute the, plants produce their food by. atmosphere That is why you are advised, a process called photosynthesis.
not to play with fireworks, Can we call photosynthesis. When food gets spoiled it produces, a chemical change. a foul smell Shall we call this change a, chemical change. Paheli said that even digestion, You must have noticed that a slice of. is a chemical change, an apple acquires a brown colour if it is.
not consumed immediately If you have, not seen this change in colour cut a. fresh slice of apple and keep it away for, 6 3 RUSTING OF IRON. some time Repeat the same activity with, a slice of potato or brinjal The change Let us get back to rusting This is one. of colour in these cases is due to the change that affects iron articles and. formation of new substances Are not slowly destroys them Since iron is used. these changes chemical changes in making bridges ships cars truck. In Chapter 5 you neutralised an acid bodies and many other articles the. with a base Is neutralisation a chemical monetary loss due to rusting is huge. change The process of rusting can be, represented by the following equation. Iron Fe Oxygen O2 from the air, A protective shield water H2O rust iron oxide Fe2O3.
For rusting the presence of both, You must have heard of the ozone layer. oxygen and water or water vapour, in our atmosphere It protects us from. is essential, the harmful ultraviolet radiation which. In fact if the content of moisture in, come from the sun Ozone absorbs this. air is high which means if it is more, radiation and breaks down to oxygen.
humid rusting becomes faster, Oxygen is different from ozone Can. So how do we prevent rusting, we call the breaking down of ozone a. Prevent iron articles from coming in, chemical change. contact with oxygen or water or both, If ultraviolet radiation were not. One simple way is to apply a coat of, absorbed by ozone it would reach the.
paint or grease In fact these coats, earth s surface and cause harm to us. should be applied regularly to prevent, and other life forms Ozone acts as a. rusting Another way is to deposit a layer, natural shield against this radiation. of a metal like chromium or zinc on iron, PHYSICAL AND CHEMICAL CHANGES 63. solutions The process is called, crystallisation, crystallisation It is an example of a.
Oh that is why my friend, physical change, Rita is always complaining. about iron articles rusting so Activity 6 9, fast She lives near the coast To be performed in the presence of. the teacher, This process of depositing a layer of zinc. on iron is called galvanisation, galvanisation The iron CAUTION. pipes we use in our homes to carry water Use only dilute sulphuric acid Be. are galvanised to prevent rusting careful while boiling water. You know that ships are made of iron, and a part of them remains under water Take a cupful of water in a beaker.
On the part above water also water and add a few drops of dilute sulphuric. drops keep clinging to the ship s outer acid Heat the water When it starts. surface Moreover the water of the sea boiling add copper sulphate powder. contains many salts The salt water slowly while stirring continuously. makes the process of rust formation Fig 6 6 Continue adding copper. faster Therefore ships suffer a lot of sulphate powder till no more powder can. damage from rusting in spite of being be dissolved Filter the solution Allow. it to cool Do not disturb the solution, Stainless steel is made by mixing iron when it is cooling Look at the solution. with carbon and metals like after some time Can you see the crystals. chromium nickel and manganese It of copper sulphate If not wait for some. does not rust more time, painted So much so that a fraction of. ship s iron has to be replaced every year Copper sulphate. Can you imagine the monetary loss to, 6 4 CRYSTALLISATION. In Class VI you have learnt that salt can, be obtained by the evaporation of sea. water The salt obtained in this manner, is not pure and its crystals are small.
The shape of the crystals cannot be seen, clearly However large crystals of pure Crystals. substances can be formed from their Fig 6 6 Crystals of copper sulphate. 64 SCIENCE, You have learnt about physical and changes that you observe around you. chemical changes Try to identify as physical or chemical changes. Chemical change Crystallisation Physical change, Chemical reaction Galvanisation Rusting. What you have learnt, Changes can be of two types physical and chemical. Physical changes are changes in the physical properties of substances. No new substances are formed in these changes These changes may. be reversible, In chemical changes new substances are produced.
Some substances can be obtained in pure state from their solutions by. crystallisation, 1 Classify the changes involved in the following processes as physical or. chemical changes, a Photosynthesis, b Dissolving sugar in water. c Burning of coal, d Melting of wax, e Beating aluminium to make aluminium foil. f Digestion of food, 2 State whether the following statements are true or false In case a. statement is false write the corrected statement in your notebook. a Cutting a log of wood into pieces is a chemical change True False. b Formation of manure from leaves is a physical change True False. PHYSICAL AND CHEMICAL CHANGES 65, c Iron pipes coated with zinc do not get rusted easily True False.
d Iron and rust are the same substances True False. e Condensation of steam is not a chemical change True False. 3 Fill in the blanks in the following statements, a When carbon dioxide is passed through lime water it turns milky. Physical and Chemical 6 Changes E very day you come across many changes in your surroundings These changes may involve one or more substances For example your mother may ask you to dissolve sugar in water to make a cold drink Making a sugar solution is a change Similarly setting curd from milk is a change Sometimes milk becomes sour Souring of milk is a change Stretched rubber band

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