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2. Magic of Chemical Reactions 24 SCHOOL SECTION MT Q.I 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. *11. *12. *13. *14. *15. 16. SCIENCE & TECHNOLOGY EDUCARE LTD. (A) Fill in the blanks : Ice changing to water is an example of ....................... change. When copper powder is heated, ....................... is formed. The substances that undergo changes are called as ....................... . Reactants are represented on ....................... . Products are represented on ....................... . Conversion of oil to fats requires ....................... as catalyst. When vegetable oil is mixed with nickel as a catalyst, and heat it with hydrogen gas ....................... are obtained on cooling. The simple form of representation of chemical reaction in words is called ....................... . If reactants or products are present as solution in excess of water, the symbol used is ....................... . According to ......................., the total mass of reactants is equal to the total mass of products during a chemical reaction. The chemical formula of POP is ....................... . The chemical reaction during which hydrogen is lost is called as ....................... . Corrosion can be prevented by using ....................... . When acids and alkalis react together, ....................... and ....................... is formed. The chemical reaction in which heat is evolved is called as ....................... reaction. When oil and fats are oxidized or even allowed to stand for a long time, they become ....................... . Answers : 1. physical 2. copper oxide 3. reactants 4. left hand side 5. right hand side 6. Nickel 7. fats 8. word equation 9. aq 10. law of conservation of mass 11. (CaSO 4) 2.H 2O 12. oxidation reaction 13. anti-rust solution, coating surface by paint, process like galvanizing and electro-plating 14. salt and water 15. exothermic reaction 16. rancid Q.I 1. (i) (ii) (iii) (iv) Ans. (B) Match the following : Column I Column II Reactants Products Fe + S (a) NaCl + H2O (b) 2CuO CuSO4 + Zn 2Cu + O2 (c) ZnSO4 + Cu HCl + NaOH (d) FeS (i - d, 4), (ii - c, 3), (iii - b, 1), (iv - a, 2). 2. (i) (ii) (iii) (iv) Ans. Column I Gain of oxygen a) Digestion (b) Iodine, Camphor (c) NaOH + HCl NaCl + H2O (d) (i - b), (ii - a), (iii - d), (iv - c). SCHOOL SECTION 1. 2. 3. 4. Column III Types of reactions Oxidation Neutralization Displacement Combination Column II Chemical change Oxidation Balanced equation Sublimatory substances 25 MT SCIENCE & TECHNOLOGY 3. (i) (ii) (iii) (iv) Ans. Q.I 1. Ans. 2. Ans. 3. Ans. 4. Ans. 5. Ans. Q.I 1. Ans. 2. Ans. 3. Ans. 4. Ans. 5. Ans. 6. Ans. 7. Ans. Q.I 1. Ans. 2. Ans. 3. Ans. 4. Ans. 26 Column I Copper Coper Sulphate Silver chloride Copper oxide (i - d), (ii - b), (iii - c), (iv - a). (a) (b) (c) (d) EDUCARE LTD. Column II Black colour Peacock blue White precipitate Reddish brown (C) State whether the following statements are true or false. If false write the corrected statement : Chemical change is a temporary change False. It is a permanent change. Camphor sublimes on heating. True. (g) indicates the physical state as solid. False. (g) indicates the physical state as gas. Conversion of quick lime to slaked lime is an example of displacement reaction. False. It is an example of combination reaction. When left over edible oil is heated, its smell turns foul and develops rancidity. True. (D) Find the odd man out : Cu, Fe, Mn, CuSO4. CuSO4 as it is a compound and rest all are elements. Conversion of milk to curd, Rusting of iron, Digestion of food, Water turns into ice. Water turns into ice as rest all are examples of chemical change. Action of heat on calcium carbonate, Action of light on silver bromide, Action of light on silver chloride, Action of sodium hydroxide on hydrochloric acid. Action of sodium hydroxide on hydrochloric acid as it is a neutralization reaction and rest are examples of decomposition reaction. Fe + S FeS, NH3 + HCl NH4Cl, H2 + Cl2 HCl, CaCO3 CaO + CO2. CaCO3 CaO + CO2, this is decomposition reaction and rest all combination reaction. , (g), (l), =. =. This sign is not used in chemical equation. SO2 = sulphur dioxide, H 2S = hydrogen sulphide, K 2CrO4 = potassium dichromate, NaNO3 = sodium nitrate. K2CrO4 as it is potassium chromate and not potassium dichromate. Photosynthesis, Digestion, Respiration, Magnetization of iron nail. Magnetisation of iron nail as it is a physical change and rest are chemical change. (E) Write the correlated terms : Solid to liquid : Melting :: ....................... : Sublimation. Solid to gas. Reactants : Breaking of bonds :: Products: ....................... . Formation of bond. Physical change : Reversible :: Chemical change : ....................... . Irreversible. BaSO4 : ....................... :: Copper sulphide : Black precipitate. White precipitate. SCHOOL SECTION MT Q.I 1. 3. 5. 7. 9. 11. (F) Classify the following into physical Rusting of iron 2. Copper sulphate dissolved in water 4. Ripening of mango 6. Magnetisation of iron nail 8. Decaying of vegetables 10 Production of energy in body. Ans. 1. 2. 3. 4. Q.I 1. 3. 5. 7. 1. 2. 3. 4. 3. Ans. 4. Ans. 5. Ans. 6. Ans. change and chemical change : Water turns into ice Bending of iron nail Digestion of food Formation of compound Formation of blood Physical change Water turns into ice 1. Copper sulphate dissolved in water 2. Bending of iron nail 3. Magnetisation of iron nail 4. 5. 6. 7. Chemical change Rusting of iron Ripening of mango Digestion of food Formation of compound Decaying of vegetables Formation of blood Production of energy in body (G) Classify the following into exothermic and endothermic reactions : Quick lime is added to water 2. Potassium chlorate is heated Sodium dissolved in water 4. Mercuric oxide is strongly heated Neutralization of NaOH and HCl 6. Calcium carbonate is strongly heated Electrolysis of water 8. Zinc reacts with dil HCl Ans. Q.II 1. Ans. 2. Ans. SCIENCE & TECHNOLOGY EDUCARE LTD. Exothermic reactions Endothermic reactions Quick lime is added to water. 1. Potassium chlorate is heated. Sodium dissolved in water. 2. Mercuric oxide is strongly heated. Neutralization of NaOH and HCl. 3. Calcium carbonate is strongly heated. Zinc reacts with dil HCl. 4. Electrolysis of water. Define the following : Reactants. Substances undergoing a chemical change are called as reactants. Products. The new substance formed as a result of chemical reaction is called as product. Word equation. The simple form of representation of chemical reaction in words is word equation. Chemical equation. The representation of chemical reaction with the help of chemical formulae is a chemical equation. Combination reaction. When two or more substances combine (mixture or compounds) to form a single product, then the reaction is called as combination reaction. Displacement reaction. When a more reactive element removes another element, having less reactivity, from its compound, this reaction is called as displacement reaction. MEMORISE : Reactivity series- Arrangement of metals in a vertical column in the order of decreasing reactivities is called reactivity series of metals. Here the most reactive metal is placed on top and less reactive is placed at the bottom.So, potassium is the most reactive metal and gold is least reactive. – Extra Information. SCHOOL SECTION 27 SCIENCE & TECHNOLOGY 7. Ans. 8. Ans. 9. Ans. 10. Ans. 11. Ans. 12. Ans. 13. Ans. 14. Ans. 15. Ans. 16. Ans. MT EDUCARE LTD. Decomposition reaction. When a single reactant has broken down to give a simple product is known as decomposition reaction. Double displacement reaction. The reaction where a precipitate is formed by exchange of ions between the reactants is called as double displacement reaction. OR A chemical reaction in which constituents (radicals or ions)of two substances mutually exchange their places to form two new substances is called as double displacement reaction. Redox reaction. When oxidation and reduction takes place simultaneously in a given chemical reaction, it is called as redox reaction. Oxidation reaction. The chemical reaction in which reactants gain oxygen to form corresponding oxide. Similarly A chemical reaction in which reactants lose hydrogen to form product is called oxidation. Reduction reaction. The chemical reaction in which reactants gain hydrogen are reduction reactions. Similarly The reaction in which reactants lose oxygen atom to form product is called reduction. Neutralization reaction. The reaction between acid and alkali to form salt and water is called as neutralization reaction. Corrosion. The slow process of decay or destruction of metal due to the effect of air, moisture, acids on it is called as corrosion. Exothermic reaction. The reaction in which heat is evolved is called as exothermic reaction. Endothermic reaction. The reaction in which heat is absorbed is called as endothermic reaction. Balanced equation. When number of atoms are same on the L.H.S. and R.H.S. of the chemical equation, then the equation is said to be a balanced equation. Q.III Give scientific reasons : *1. Grills of doors and windows are always painted before they are used. Ans. 1. Railings, iron bridges, grills of doors and windows, railway coaches, steel furniture, and bodies of truck, cars, buses are made of iron. 2. To protect them from rusting, a coating of paint is applied. By doing this, air and moisture cannot come in contact with the iron object and hence rusting doesn’t takes place. So, grills of doors and windows are always painted before they are used. *2. Physical states of reactants and products are mentioned while writing a chemical equation. Ans. 1. The equation that gives more information about the chemical reaction is known as more informative or information giving equation. 2. The chemical equation can be made more informative in three ways : (a) By indicating the physical states of reactants and products. (b) By indicating the heat changes taking place in the equation. (c) By indicating the conditions under which the reaction takes place. So, physical states of reactants and products are mentioned while writing a chemical equation. 28 SCHOOL SECTION MT *3. Ans. *4. Ans. *5. Ans. 6. Ans. 7. Ans. EDUCARE LTD. SCIENCE & TECHNOLOGY Potassium ferrocyanide is stored in dark coloured bottles and kept away from sunlight. 1. Potassium ferrocyanide, (molecular formula is K 4[Fe(CN)6].3H2O) is a yellow coloured compound. 2. If this compound gets exposed to sunlight then it will undergo decomposition reaction. 3. Therefore, potassium ferrocyanide is stored in dark coloured bottles and kept away from sunlight. Iron articles rust readily whereas steel which is also made of iron will not undergo corrosion. 1. Iron is a widely used metal but if it used in the pure form, it may rust. 2. When a small amount of carbon (varying from 0.1% to 1.5% )is mixed with iron, we get an alloy called steel. 3. This alloy of iron is hard and strong and is used for making nails, screw, bridges, railway lines, ships, construction of buildings, vehicles. 4. An important property of alloy is that they resist corrosion. So, iron articles rust readily whereas steel which is also made of iron will not undergo corrosion. MEMORISE : An alloy is a homogeneous mixture of two or more metals( or a metal and small amount of non-metal). If iron metal is alloyed with other metals like chromium and nickel, we get stainless steel that does not rust at all. – Extra Information. Edible oil is not allowed to stand for a long time in an iron or tin container. 1. Fats and edible oil when allowed to stand for a longer time in iron or tin container becomes rancid. 2. The condition produced by oxidation of fats and oils in food marked by unpleasant smell and taste is called rancidity. When the oil is heated, it starts frothing and smells foul. 3. If the food is cooked in rancid oil, it gives an unpleasant smell and taste, making it unfit for consumption. So, edible oil is not allowed to stand for a long time in an iron or tin container. Rusting of iron is a chemical change. 1. When iron is exposed to air, it gets oxidized by oxygen in air in the presence of moisture to form reddish brown coloured hydrated iron oxide. This process is called rusting of iron. The number of water molecules in the rust varies. 4Fe (s) + 3O 2(g) + 2xH2O(l) 2Fe 2 O 3 .H 2O (s) Iron Oxygen Water Hydrated iron oxide 2. The chemical properties of iron oxide are different from iron and oxygen. 3. We cannot obtain back iron from rust(iron oxide) by simple method i.e. change is irreversible. Hence rusting of iron is a chemical change. Chemical change is always associated with exchange of energy. 1. Chemical reaction or changes may take place spontaneously by bringing reactants in contact. This is usually accompanied by release of heat. 2. During a chemical reaction, the bonds between the atoms of the reactants break. This is made possible by bringing reactants in contact and then by supplying energy like heat, electricity or light. As a result, products are formed. Thus, a chemical reaction is always associated with an exchange of energy. SCHOOL SECTION 29 MT SCIENCE & TECHNOLOGY 8. Ans. 9. Ans. 10. Ans. EDUCARE LTD. Conversion of ice into water is a physical change. 1. On heating, ice melts into water and on the other hand when water is cooled, it freezes into ice. 2. In this change, only the physical property of water i.e state of water changes as both ice and water chemically are water only. Therefore, no new substance is formed. Hence, conversion of ice into water is a physical change. Formation of a compound is a chemical change. 1. Compound is a substance produced by the chemical reaction between two or more elements in a fixed proportion. 2. Both physical and chemical properties of the compound are different from the properties of its constituent elements. 3. A new substance is formed, which can not be converted into original substance. Hence formation of a compound is a chemical change. Silver salts are kept in dark coloured bottles. 1. A chemical reaction that proceeds by absorption of light is called a photochemical reaction. 2. Eg. When silver bromide is exposed to light, yellow colour of silver bromide changes to grey colour. Silver bromide is decomposed to form grey silver metal and bromine gas is liberated. Sunlight + Br 2(g) 2AgBr(s) 2Ag(s) Silver bromide Silver metal Bromine gas. So, Silver salts are kept in dark coloured bottles. Q.IV 1. Ans. Distinguish between : Physical change and Chemical change. 2. Ans. Exothermic reaction and Endothermic reacion. Exothermic reaction Endothermic reaction 1. The reaction where heat energy 1. The reaction where heat energy is evolved or liberated is called is absorbed is called as as exothermic reaction. endothermic reaction. 2. Temperature of the reaction 2. Temperature of the reaction mixture rises. mixture lowers. 3. Generally, the reactions are fast. 3. Generally, the reactions are slow. 4. Products are more stable. 4. Reactants are more stable. 5. These reactions take place at 5. These reactions take place at lower temperatures. high temperatures. 6. Eg.: Neutralization reaction. 6. Eg.: Calcium is strongly heated. 30 Physical change 1. In this change, the composition of substance does not change and no new substance is formed. 2. There is a change only in physical properties. 3. This change is temporary. 4. The original substance can be recovered by simple means. 5. Eg.: Steam is condensed. Chemical change 1. In this change, the composition of substance changes and a new substance is formed. 2. There is a change in both physical and chemical properties. 3. This change is permanent. 4. The original substance cannot be recovered by simple means. 5. Eg.: Ripening of fruit, milk is converted to curd. SCHOOL SECTION MT Q.V *1. Ans. *2. Ans. *3. Ans. *4. Ans. EDUCARE LTD. SCIENCE & TECHNOLOGY Answer the following in detail : What do you observe when H2S gas is passed through cadmium chloride solution, name the type of reaction? When hydrogen sulphide gas is passed through cadmium chloride solution, it gives a yellow precipitate of cadmium sulphide and hydrochloric acid. CdCl 2(aq) + H 2S (g) CdS(l) + 2HCl(aq) It is a double displacement reaction. What do you understand by the term redox reaction? Explain with one example. 1. When oxidation and reduction takes place simultaneously in a chemical reaction, it is termed as redox reaction. 2. Eg.: When sulphur dioxide reacts with hydrogen sulphide, it forms water and sulphur. SO 2 + 2H2S 2H2O + 3S In this reaction, SO2 is changing to S. This is removal of oxygen which is called as reduction. So, SO2 is reduced to S. H2S is changing to H2O. This is addition of oxygen which is called as oxidation. So, H2S is oxidized to H2O. What is corrosion? Do gold ornaments corrode, if not why? 1. The slow process of decay or destruction of metal due to effect of air, moisture, acids on it is called as corrosion. 2. Gold is a yellow shining metal. Gold metal does not corrode because it is a highly unreactive metal that remains unaffected by air, water vapour, and other gases in the atmosphere. Gold does not tarnish and retains its luster for years. Since gold does not corrode, gold ornaments look new after years. break. 3. This is achieved by bringing reactants in contact with each other and then by supplying energy in the form of either heat, light or electricity. 4. This results in breaking of bonds in the reactants and rearrangement of atoms of reactants and formation of new bonds in the product. 5. Thus, a chemical reaction is always associated with exchange of energy. State the neutralization. 1. The reaction between acid and base to form salt and water is called as neutralization reaction. Acid + Base Salt + Water 2. When an acid is treated with base, the base neutralizes the acid and destroys its acidity. Since an acid and base neutralize each other's effect, it is called as neutralization reaction. 3. Eg.: When hydrochloric acid reacts with sodium hydroxide, then a neutralization reaction takes place to give salt and water. NaOH(aq)+ HCl (aq) NaCl (aq) + H2O (l) MEMORISE : We can carry out this reaction in the laboratory and phenolphthalein is used as an indicator. – Extra Information. SCHOOL SECTION 31 SCIENCE & TECHNOLOGY 5. Ans. 6. Ans. *7. Ans. 32 MT EDUCARE LTD. What are the steps of writing a chemical equation? 1. The symbols or molecular formulae of the reactants are written on the left hand side and products are on the right hand side. 2. Reactants and products are connected with an arrow () pointing towards product side. 3. Whenever there are two or more reactants, a plus (+) sign is written between each of them. Similarly, if there are two or more products, a plus sign is written between them. 4. Certain reactions have to be carried out under specific condition such as temperature, pressure, catalyst. These condition are mentioned on the arrow pointing from reactants to product. 5. The physical states of reactants and products are also mentioned in a chemical equation to make it more informative. 6. The notations like g,l,s,aq are written in brackets as subscripts along with symbols/formulae of reactants and products. or (g) - Gas (l) - Liquid (s) - Solid (aq) - Aqueous solution - Precipitate. Take finely powdered zinc and allow it to react with CuSO4. Then take zinc granules and carry out the same reaction. Which reaction takes place faster ? 1. The reaction is as follows : When zinc reacts with copper sulphate solution to give a water soluble compound zinc sulphate and reddish brown deposit of copper. + CuSO4(aq) ZnSO 4(aq) + Cu (s) Zn (s) Zinc Copper sulphate Zinc sulphate Copper 2. In solid reactants, the rate of a reaction depends upon size of particles. Smaller the size of particles, quicker is the reaction. This is because, in case of large solid reactants, only the molecules on surface are available for reaction. But if the reactants are finely powdered, the total surface area on all the smaller particles become much more and hence more number of molecules become available for reaction. 3. So, the reaction takes place faster with powdered zinc than zinc granules. We feel fresh while on a morning walk in natural surroundings. Why don’t we feel the same after 10 a.m. and during rush hours ? Write a chemical reaction to support your statement. 1. During early morning more amount of O 2 is available for cellular respiration. So, glucose is completely oxidise to release energy. C 6 H 12 O 6 + O 2 CO 2 + H 2 O + Energy (38 ATP) 2. As the day progresses the level of O2 decreases as compare to early morning this is due emission of other gases under this condition glucose releases only 2 ATP (energy) molecules. 3. Since, more amount of energy is released in presence of O2 and less amount of energy is released due to insufficient oxygen. SCHOOL SECTION MT Q.VI 1. Ans. 2. Ans. Ans. 3. Ans. MEMORISE : The rate of reaction is change in concentration of reactants and products in unit time. The rate of reaction also depends on : Nature of reactants, Size of particles, Concentration of reactants, Temperature and effect of catalyst. A catalyst is used to bring about a chemical reaction at low temperature and at a faster rate that reduces the production cost and increases – Extra Information. profitability. Answer the following questions in one sentence each : What are the different types of reactions? There are four different types of reactions that are : 1. Combination reaction 2. Displacement reaction 3. Decomposition reaction 4. Double displacement reaction. Carbohydrates like rice, potato, sago etc are major sources of energy in our diet. During digestion, these are broken down to glucose. Glucose combines with oxygen in our body and provides energy. C 6H 12O 6(aq) + 6O 2(g) 6CO 2(g) + 6H2O(l) + Energy 1. Is this an exothermic reaction? Since energy is released, it is an exothermic reaction When edible oil is converted to fats, what reaction is it? Express it in words. 1. Conversion of edible oils to fats is called as hydrogenation reaction. 2. When H2 gas is passed through edible oil in presence of Nickel which acts as a catalyst at high temperature. It gets converted into fats, this reaction is called as hydrogentation reaction. Edible oil 4. Ans. 5. Ans. 6. Ans. 7. Ans. SCIENCE & TECHNOLOGY EDUCARE LTD. + Hydrogen gas Ni/ Fats What was the colour of precipitate formed ? When you add potassium chromate (K2CrO4) to barium sulphate solution (BaSO 4). + BaSO4 BaCrO4 + K 2SO 4 K 2 CrO 4 Potassium Barium Barium Potassium chromate sulphate chromate sulphate Name the precipitate. Barium chromate (BaCrO4) which is yellow in colour. Write balanced chemical equation. K 2 CrO 4 + BaSO4 BaCrO4 + K 2SO 4 According to you, is it a displacement reaction or double displacment reacion ? It is a double displacement reaction. Q.VII Balance the following chemical reactions with the help of balanced equations : + Cl 2 HCl 1. H2 + Cl 2 2HCl Ans. H 2 2. NH 3 + HCl NH4Cl Ans. The equation is already balanced, so it is a self balanced equation. SCHOOL SECTION 33 MT SCIENCE & TECHNOLOGY 3. Ans. 4. Ans. 5. Ans. 6. Ans. 7. Ans. 8. Ans. ZnS 2ZnS + + Ans. Ans. Ans. Ans. Ans. Ans. Ans. Ans. 34 ZnO 2ZnO + + SO2 2SO2 Heat CaCO3 CaO + CO2 The equation is already balanced, so it is a self balanced equation. H2S + O2 H2O + SO2 2H2S + 3O2 2H2O + 2SO2 AgNO3 + H2S HNO3 + Ag 2S 2AgNO3 + H 2 S 2HNO 3 + Ag2S NaOH + CO2 Na2CO3 + H2O 2NaOH + CO 2 Na 2CO 3 + H 2 O Identify the following reactions as combination, decomposition, displacement, double displacement reaction. 1. H2 + Cl 2 2HCl Combination reaction. Heat 2Hg + Thermal decomposition reaction. 3. NH 3 + HCl NH4Cl Combination reaction. 4. BaCl2 + H2SO4 BaSO4 Double displacement reaction. 5. Zn + 2HCl ZnCl2 Displacement reaction. 6. CuSO4 + Fe FeSO4 Displacement reaction. 2. 2HgO Ans. O2 3O2 EDUCARE LTD. O2 + 2HCl + H2 + Cu Heat 7. 2KClO 3 2KCl + Thermal decomposition reaction. 8. 2KI + Cl 2 2KCl + Displacement reaction. 9. C + O2 CO2 Combination reaction. 10.CaO + H2O Ca(OH)2 + Combination reaction. 3O2 I2 heat MEMORISE : To get the molecular formula of a compound: Eg. : Sodium chloride Symbol Na Cl Valency 1 1 Criss cross Na 1 Cl 1 i.e. NaCl – Extra Information. SCHOOL SECTION MT 16. EDUCARE LTD. Write the formulae of the following : Name of compound Potassium chromate Iron sulphide Copper oxide Hydrogen sulphide Sulphur dioxide Carbonic acid Plaster of Paris Potassium nitrate Calcium carbonate Quick lime or calcium oxide Calcium hydroxide or slaked lime Silber bromide Calcium sulphide Barium sulphate Ethyl alcohol Methane Ans. Ans. Ans. Ans. Ans. Ans. Ans. SCIENCE & TECHNOLOGY Formula K 2 CrO 4 FeS CuO H2S SO 2 H 2CO 3 (CaSO 4) 2.H 2O KNO 3 CaCO3 CaO Ca(OH) 2 AgBr CaS BaSO4 C 2H 5OH CH 4 1. Sulphur dioxide reacts with hydrogen sulphide When sulphur dioxide reacts with hydrogen sulphide to give sulphur and water. SO 2(g) + 2H 2S (g) 3S (g) + 2H2O(l) Sulphur dioxide Hydrogen sulphide Sulphur Water 2. Copper is exposed to air. When copper is exposed to air, copper gets oxidized to form black coloured copper oxide. 2Cu(s) + O 2(g) 2CuO(s) Copper Oxygen Copper oxide 3. Iron sulphide reacts with sulphuric acid. When iron sulphide reacts with sulphuric acid to give ferrous sulphate and hydrogen sulphide gas is liberated. FeS (s) + H 2SO 4(aq) FeSO 4(aq) + H 2S (g) Ferrous sulphide Sulphuric acid Ferrous sulphate Hydrogen sulphide 4. Iron reacts with sulphur. When iron reacts(heated) with sulphur to give iron sulphide. FeS (s) Fe (s) + S (s) Iron Sulphur Iron sulphide 5. Plaster of Paris is mixed with water. When Plaster of Paris is mixed with proper quantity of water, it shows a remarkable property of setting into a hard mass called gypsum. (CaSO4)2, H2O + 3H2O 2(CaSO4, 2H2O) + Heat energy Plaster of Paris Gypsum 6. Cement with sand and gravel reacts with water at new construction sites. Cement with sand and gravel reacts with water to form concrete that imparts strength to the building. This is an exothermic reaction. 3CaO.Al2O3 + 6H2O(l) 3CaO.Al2O3.6H2O + Heat Tricalcium aluminate Concrete 7. Calcium oxide (quick lime) is mixed with water. When calcium oxide reacts with vigorously with water to form calcium hydroxide(slaked lime). Since a large amount of energy is released, it is an exothermic reaction. SCHOOL SECTION 35 SCIENCE & TECHNOLOGY Ans. Ans. Ans. Ans. Ans. Ans. Ans. 36 MT EDUCARE LTD. CaO (s) + H2O (l) Ca(OH) 2 + Heat Calcium oxide Water Calcium hydroxide 8. Potassium nitrate is mixed with water. When potassium nitrate is mixed with water, potassium nitrate dissolves in water. There is absorption of heat (endothermic reaction) and so the temperature of the solution falls. KNO 3(s) + H2O (l) KNO3(aq) + Heat Potassium nitrate Water Potassium nitrate 9. Sodium hydroxide is mixed with water. When sodium hydroxide is mixed with water, sodium hydroxide dissolves in water. Since heat is liberated (exothermic), the temperature of the solution rises. NaOH (s) + H2O (l) NaOH(aq) + Heat Sodium hydroxide Water Sodium hydroxide 10.Glucose combines with oxygen during the process of respiration. When glucose combines with oxygen in the cells of our body during the process of respiration to form carbon-dioxide and water along with the production of energy. Since energy is released, it is an exothermic reaction. C 6H 12O 6(aq) + 6O 2(g) 6CO 2(g) + 6H2O(l) + Energy Glucose Oxygen Carbon dioxide Water 11.Calcium carbonate is heated. When calcium carbonate is heated, it decomposes to form calcium oxide (quick lime) and carbondioxide gas. As heat is absorbed, it is an endothermic reaction. Since the decomposition is brought by heat, it is also called as thermal decomposition. Heat CaCO 3(s) CaO (s) + CO 2 Calcium carbonate Calcium oxide Carbon dioxide 12.Sugar (sucrose) is heated strongly. When sucrose is heated strongly, it breaks down to give black coloured carbon and water. As heat is absorbed, it is an endothermic reaction. Since the decomposition is brought by heat, it is a thermal decomposition. Heat C 12 H 22 O 11(s) 12C (s) + 11H 2O(g) Sugar Carbon Water 13.Silver bromide is exposed to light. When silver bromide is exposed to light, yellow colour of silver bromide changes to grey colour. Silver bromide is decomposed to form grey silver metal and bromine gas is liberated. This reaction is used in black and white photography during the process of developing. Sunlight 2AgBr(s) + Br 2(g) 2Ag(s) Silver bromide Silver metal Bromine gas 14.Silver chloride is exposed to light. When silver chloride is exposed to light, white colour of silver chloride changes to grey colour. Silver bromide is decomposed to form grey silver metal and chloride gas is liberated. This reaction is used in black and white photography during the process of developing. Sunlight 2AgCl(s) + Cl 2(g) 2Ag(s) Silver chloride Silver metal Bromine gas SCHOOL SECTION MT Ans. Ans. Ans. Ans. Ans. Ans. Ans. Ans. EDUCARE LTD. SCIENCE & TECHNOLOGY 15.Calcium sulphide reacts with dilute hydrochloric acid. When calcium sulphide reacts with dilute hydrochloric acid to give calcium chloride and hydrogen sulphide gas is liberated. CaS (s) + 2HCl(l) CaCl 2(s) + H2S(g) Calcium sulphide Hydrochloric acid Calcium chloride Hydrogen sulphide 16.Zinc reacts with copper sulphate. When zinc reacts with copper sulphate, zinc being more reactive than copper displaces copper to give colourless zinc sulphate and reddish brown deposit of copper. So, it is a displacement reaction. The blue colour of copper sulphate fades due to formation of colourless zinc sulphate. CuSO 4(s) + Zn (s) ZnSO 4(aq) + Cu (s) Copper sulphate Zinc Zinc sulphate Copper 17.Iron reacts with copper sulphate. When iron reacts with copper sulphate, iron being more reactive than copper displaces copper to give light green colored solution of iron sulphate and reddish brown deposit of copper. So, it is a displacement reaction. The blue colour of copper sulphate fades due to formation of light green solution of zinc sulphate. CuSO 4(s) + Fe (s) FeSO 4(aq) + Cu (s) Copper sulphate Iron Iron sulphate Copper 18.Copper chloride reacts with potassium iodide. When copper chloride reacts with potassium iodide, it gives a brown coloured precipitate of cupric iodide and potassium chloride. This reaction is a double displacement reaction. 2CuCl2(aq) + 2KI(aq) CuI2 + 2KCl Copper chloride Potassium iodide Cuppric iodide Potassium chloride 19.Silver nitrate reacts with sodium chloride solution. When silver nitrate solution reacts with sodium chloride solution it gives a white precipitate of silver chloride and sodium nitrate. This reaction is a double displacement reaction. AgNO3(aq) + NaCl (aq) AgCl + NaNO3(aq) Silver nitrate Sodium chloride Silver chloride Sodium nitrate 20.Barium sulphide reacts with zinc sulphate solution. When barium sulphate reacts with zinc sulphate solution, it gives a white precipitate of barium sulphate and zinc sulphide. This reaction is a double displacement reaction. BaS(aq) + ZnSO 4(aq) BaSO4 + ZnS (aq) Barium sulphide Zinc sulphate Barium sulphate Zinc sulphide 21.Aluminium is burnt in air. When aluminium is burnt in air, it gets oxidized to form aluminium oxide or alumina. 4Al (s) + 3O 2(g) 2Al 2O 3(s) Aluminium oxygen Aluminium oxide 22.Sodium metal reacts with ethyl alcohol. When sodium metal reacts with ethyl alcohol to give sodium ethoxide and hydrogen gas is liberated. The hydrogen atom of the hydroxyl (OH)group is replaced by a sodium atom, forming sodium ethoxide. 2C 2H5OH(l) + 2Na (s) 2C 2H 5ONa(g) + H2 Ethyl alcohol Sodium Sodium ethoxide Hydrogen SCHOOL SECTION 37 SCIENCE & TECHNOLOGY Ans. Ans. Ans. Ans. Ans. Ans. 38 MT EDUCARE LTD. MEMORISE : Sodium ethoxide is a strong base. It is commercially available as a dry yellow solid, or as a solution in ethanol. – Extra Information. 23.Hydrogen gas is passed over carbon. When hydrogen gas is passed over carbon, it gives methane. + 2H 2(g) CH 4(g) C (s) Carbon Hydrogen Methane 24.Hydrogen gas is passed over copper oxide. When hydrogen gas is passed over copper oxide, it gives a pinkish brown coating of copper. CuO(s) + H 2(g) Cu (s) + H2O (l) Copper oxide Hydrogen Copper Water 25.Ozone is subjected to heat and light. When ozone is subjected to heat and light, it gives oxygen gas and nascent oxygen. Light, O2 + [O] O 3 Ozone Oxygen Nascent oxygen MEMORISE : Nascent oxygen is a single oxygen atom, a short-lived free radical of oxygen. Stratospheric ozone protects us from harmful ultra-violet radiation from the Sun. However, in the troposphere, ozone is dangerous to our health. Its not true that we don't want any ozone in the troposphere. We need low levels in the air to form hydroxyl radicals (OH) to clean the air of harmful chemicals. However, high concentrations of ozone are harmful to our health and damage plants. The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer between about 10 km and 50 km above the surface (or between about 6 and 31 miles). Here it filters out photons with shorter wavelengths (less than 320 nm) of ultraviolet light, also called UV rays, (270 to 400 nm) from the Sun that would be harmful to most forms of life in large doses. – Extra Information. 26.Barium sulphate reacts with carbon. When barium sulphate reacts with carbon, barium sulphate gets reduced to barium sulphide and carbon gets oxidized to carbon monoxide. BaSO4(aq) + 4C (s) BaS + 4CO(g) Barium sulphate Carbon Barium sulphide Carbon monoxide 27.When an iron rod is exposed to air. When an iron rod is exposed to air, it gets oxidized by oxygen in air in the presence of moisture to form reddish brown coloured hydrated iron oxide. This process is called rusting of iron. The number of water molecules in the rust varies. 4Fe (s) + 3O 2(g) + 2xH2O(l) 2Fe 2O 3.xH 2O (s) Iron Oxygen Water Hydrated iron oxide 28.Sodium hydroxide reacts with hydrochloric acid. When sodium hydroxide reacts with hydrochloric acid, it undergoes neutralization reaction to give sodium chloride and water. NaOH(aq) + HCl (aq) NaCl (aq) + H2O (l) Sodium hydroxide Hydrochloric acid Sodium chloride Water Base Acid Salt SCHOOL SECTION MT SCIENCE & TECHNOLOGY EDUCARE LTD. Positively charged radicals or basic radicals or cations Monovalent cations H+ Hydrogen ion Na+ Sodium ion K+ Potassium ion Ag+ Silver ion NH4+ Ammonium ion Cu+ Cuprous ion (I) Divalent cations Mg+2 Magnesium ion Ca+2 Calcium ion Cu +2 Cupric ion (II) Fe+2 Ferrous ion (II) Zn+2 Zinc iron Negatively charged radicals or acidic radicals or anions F– Fluoride ion Cl– Chloride ion Br– Bromide ion I– Iodide ion OH– hydroxide ion HCO3 bicarbonate ion Divalent anions O–2 Oxide ion CO32 Carbonate ion SO42 sulphate ion S–2 sulphide ion Trivalent cations Trivalent anions Al Aluminium ion Fe+3 Ferric ion (III) N–3 nitride ion PO43 phosphate ion Cr+3 chromium ion BO43 borate ion +3 SCHOOL SECTION 39 MT SCIENCE & TECHNOLOGY EDUCARE LTD. ACTIVITY BASED QUESTIONS ACTIVITY : 2.1 Q. Take a table spoon full of copper powder in a china dish. Heat it strongly. What changes do you observe ? ACTIVITY : 2.2 Q. Take a small piece of aluminium wire and burn it. Record your observations. Remove a tungsten wire from a fused bulb. Try to ignite it. What do you observe ? ACTIVITY : 2.3 Q. Add potassium chromate (K2CrO4) to barium sulphate (BaSO4) solution. Note your observations. ACTIVITY : 2.4 Q. Add a small quantity of dil.H2SO4 to FeS very carefully, (under supervision of your teacher). Touch the test tube. Also experience the odour. What do you observe ? ACTIVITY : 2.5 Q. Ans. Heat camphor in a porcelain dish. Keep a funnel plugged with cotton over the dish before you heat. What do you observe when camphor burns ? What happens when the apparatus is cooled ? Complete the table with reference to the activities (2.1 to 2.5). Activity Change in colour Evolution of gas Change in Change in temperature state 2.1 Black Yes Yes No 2.2 Black Yes Yes Comparous powder 2.3 Black Hydrogen sulphide No Yes 2.4 Substances Black Yes Yes 2.5 Sublime Carbon smoke ACTIVITY : 2.6 Q. Ans. 40 Take a small piece of used paper. Weight it on an electronic balance which will be readily available in your nearby grocery shop. Burn the piece of paper and now weigh the ash. What do you observe about the initial and final weighs? What can you infer ? Suppose the weight of small piece of used paper is 2 gms. After burning the piece of paper the weight of ash remains the same i.e. 2 gms. So, we observe that the weight remains the same. This is due to law of conservation of mass. SCHOOL SECTION MT EDUCARE LTD. SCIENCE & TECHNOLOGY The total mass of the reactant is equal to the total mass of the products during a chemical reaction. Therefore chemical equation needs to be balanced. ACTIVITY : 2.6 Q. Ans. Rehana and Reshma were having fun with colours in their drawing class. Rehana mixed few drops of red colour with white colour and got pink colour. Reshma mixed yellow with red colour to get orange shade. They also prepared violet by mixing red and blue and grey by mixing black and white colours. When you mix “VIBGYOR” colours, what colour do you get ? When VIBGYOR colours are mixed you get one colour that is white if the colours are faint as in rainbow. ACTIVITY : 2.8 Q. Ans. Take a small quantity of detergent powder or washing soda in your hand and add a little water to it. What do you feel ? Is there any change in temperature when water is added to detergent ? When we add water to detergent powder or washing soda in our hands, it is slippery to touch. Yes, there is change in temperature, temperature increases. ACTIVITY : 2.9 Q. Ans. Take 100 ml of distilled water in two polythene bottles. (This prevent heat loss.) Note the temperature of water in both bottles. Add about 5 gm of potassium nitrate (KNO3) to one bottle stir well. Note temperature of the solution. Add 5 gm of NaOH to the other bottle. Note the solution temperature. What do you observe in both the cases ? What inferences can you draw ? At the start, temperature of distilled water in two bottles was suppose 60ºC. When we add KNO3 to one of the bottles, temperature of solution falls down to 50ºC, this is because there is absorption of heat during the reaction. When we add NaOH to other bottle, there is rise in temperature as there is evolution of heat during this reaction. ACTIVITY : 2.10 Q. Ans. Marry was helping her mother to make brown sugar for pudding. After sometime she obtained a black mass instead of brown with burning smell. What do you think might have happened ? Brown sugar is made by heating the sugar, but due to excessive heating the sugar burnt to form black coloured carbon. ACTIVITY : 2.11 Q. Ans. Take a spatula full of silver bromide (Your teacher will help you get it.) on a watch glass. Note its colour. Place the watch glass in sunlight. Observe the colour after some time. When we take silver bromide on a watch glass its colour is pale yellow. When we place this watch glass in sunlight the colour of silver bromide turns grey. SCHOOL SECTION 41 SCIENCE & TECHNOLOGY MT EDUCARE LTD. ACTIVITY : 2.12 Q. Ans. Take two completely used cells out of a wall clock, transistor, tape recorder, etc. Remove the material from inside. You will get a can that is made of zinc. Press and make it flat. Dip the zinc strip in copper sulphate solution (A). Let there be copper sulphate solution in another beaker B for comparison. Keep another plain zinc strip also for comparison. Remove the zinc strip after about 5 minutes. Compare 1. Intensity of blue colour of CuSO4 in beaker A and beaker B. 2. The colour of the zinc strips. 1. Intensity of blue colour of CuSO4 in beaker A fades away and intensity of blue colour of CuSO4 in beaker B remains the same. 2. The colour of the zinc strip turns brown. ACTIVITY : 2.14 Q. Ans. During festivals all of you have fun while bursting crackers. When crackers burn, you will find an ash residue after they are burnt. What reaction has taken place ? The reaction which has taken place while burning crackers is oxidation reaction. Crackers are made up of phosphorus and magnesium powder which gives the sparkling light. On burning they form an ash consisting of oxides P4O10, MgO and Mg3N2. ACTIVITY : 2.15 Q. Ans. Have you ever peeped into the store room of your home ? If you have, you must have seen some old and out of use articles made of iron. They are usually covered with a reddish layer. Do you know what red layer is called ? The reddish brown colour is deposited over the surface of iron is because of oxidation i.e. formation of Fe2O3.H2O. ACTIVITY : 2.16 Q. Ans. 42 After you have your dinner tonight, wash your own plate with soap/ detergent. What colour change is observed when soap/detergent is applied ? Can you name the type of reaction ? The yellow oily left over stains turn red/orange because of neutralization. SCHOOL SECTION MT SCIENCE & TECHNOLOGY EDUCARE LTD. QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 13) 1. (a) Name the reactants and products in equation. C12H 22O 11(s) + H 2O(aq) Ans. dil.HCl 323 K, alcoholic In the given reaction : Reactants : C 12 H 22 O 11(s) + (Sugar) Products : C 6 H 12 O 6(s) + Glucose C6H12O6 + C6H12O6 H 2O (aq) Water C 6 H 12 O 6(s) Fructose (b) What is the name of the process in equation ? n(H2C = CH2) Ans. high temp. ( ) high pressure H | C | H H | C | H n Ethylene Polyethylene The name of the process is POLYMERIZATION. QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 16) 1. Ans. 2. Ans. Paste of substance ‘A’ is used to decorate the ceiling of your home. (a) Name the substance A and write its formula. (b) Write the reaction of substance A with H2O. State the name of the product (B). (c) Where and how is ‘B’ useful ? (a) The substance A is plaster of Paris and its formula is 2 CaSO4.H2O. (b) The reaction of A with H2O is 2CaSO 4.H2O + 3H2O 2CaSO4.2H2O Plaster of Paris Gypsum (B) + Heat (c) Gypsum is the raw material used in manufacturing cement. Will it be possible for you to decompose water by heat or light energy ? If you pass current from a 6 volt battery is decomposition of water possible ? If you take pure water it is not possible to decompose water by heat or light energy or using a 6 volt battery. But if you add a few drops of acid to water then it is possible to decompose acidulated water by passing current from a 6 volt battery. QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 19) 1. Ans. When copper articles are exposed to light and moisture. Do they undergo corrosion ? Copper oxidises to form black copper oxide. Further copper oxide slowly reacts with CO2 in air to form copper carbonate which is green in colour. Thus, copper articles are exposed to light and moisture, they undergo corrosion to form the green coating on its surface. SCHOOL SECTION 43 SCIENCE & TECHNOLOGY MT EDUCARE LTD. 2. Ans. What happens to silver ornaments ? Exposure to light has no action on silver ornaments. But if the air is contaminated with H2S, the silver is blackened due to the formation of a thin film of black silver sulphide (Ag2S) on the surface. Thus, black coating is formed on silver ornaments. 3. What according to you is the reason for aluminium utensils regaining their original shine when green leafy vegetables are boiled in them ? Aluminium utensils become dull after a long time due to oxidation of Al to Aluminium oxide (Al 2 O 3 ). Leafy vegetables contain chlorophyll and chlorophyll has a capacity to produce reducing agent. When leafy vegetables are boiled in dull aluminium utensils, Al 2O3 is reduced to Al and thus regain their original shine. Ans. 4. Ans. 5. Ans. 6. Ans. 7. Ans. 44 Visit an oil merchant, request him to give you 100 ml of left over edible oil from the tin. Heat it in a container. Note your observation. When leftover edible oil is heated, it undergoes oxidation and starts frothing up and its smell turns foul. Find out the names of some natural antioxidants. Now a days many antioxidants are available in pharmacies. Can you list some brand names ? Antioxidants are the compounds which prevent the oxidation or deterioration of food. Naturally occurring many fruits contain antioxidants such as apple, strawberry, etc., dry fruits like walnut, almonds, etc., vegetable like capsicum, papaya, tomato, carrots, etc. -carotene and lycopene are natural antioxidants. Many antioxidants are available in pharmacies which contain BHA (Butylated hydroxy anisole), BHT (Butylated hydroxy toluene). Kurkure, chips, fryums, etc. are stored in air tight containers. Is that enough to prevent oxidation ? No. It helps to slow down oxidation. What more steps are taken to prevent oxidation of edible articles ? To prevent oxidation of the edible articles, the bags used to wrap the edible articles are flushed with an inert gas such as nitrogen. SCHOOL SECTION MT EDUCARE LTD. SCIENCE & TECHNOLOGY HOTS QUESTIONS & ANSWERS 1. Ans. 2. Ans. 3. Ans. 4. Ans. Meena and Rakesh cleaned utensils used for cooking with the help of ash and soap respectively. Who must have got the best results ? Why ? Rakesh must have got the best results after cleaning the utensils by scap. Edible oils are used while cooking. They are organic compounds made up of alcohols and carboxylic acids. They are neutralized by alkaline soaps. Ash cannot bring this kind of result. When washing soda is rubbed on wet palms warmness is experienced. Is the reaction exothermic or enothermic ? Why ? When washing soda dissolves in water there is evolution of heat which we feel on our palm, it is exothermic reaction. Imagine you are preparing halwa for the first time and you forget to turn off the gas after the preparation was over. What would happen ? Why ? The sugar in the halwa get overheated and breakdown to give a simple product C + H2O. The halwa would turn in to black mass with burning smell. When copper articles are exposed to light and moisture. Do they undergo corrosion ? (a) Copper oxidises to form black copper oxide. (b) Further copper oxide slowly reacts with CO 2 in air to form copper carbonate which is green in colour. (c) Thus, copper articles are exposed to light and moisture. They undergo corrosion to form the green coating on its surface. SCHOOL SECTION 45 MT SCIENCE & TECHNOLOGY EDUCARE LTD. GLOSSARY Galvanizing Electro-plating Ester Carboxylic acid Alcohol Gravel Sago Precipitate Nascent oxygen Catalyst Aqueous solution Voltameter Ions Oxidizing agent Reducing agent Formula Symbol : Process of depositing a thin layer of zinc metal on iron objects to prevent corrosion. : Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. : Esters are usually derived from an inorganic acid or organic acid in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group, and most commonly from carboxylic acids and alcohols. : Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group. : In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-OH) is bound to a carbon atom, usually connected to other carbon or hydrogen atoms. : Gravel is a rock that is of a specific particle size range. Specifically, it is any loose rock that is larger than 2 mm (0.079 in) in its smallest dimension (about 1/12 of an inch) and no more than 64 mm (2.5 in). : Sago is a starch extracted from the pith of sago palm stems. : Solid insoluble substance sometimes produced when 2 solutions are mixed or a gas is passed into a solution : It is a single oxygen atom, a short-lived free radical of oxygen. : A substance whose mere presence affects the rate of chemical reaction without undergoing itself any chemical change. : Solution in which solvent is water. : A scientific instrument used for measuring quantity of electricity. It should not be confused with a voltmeter which measures electric potential. An alternative name is coulometer. : An atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. : The substance that gives oxygen or removes hydrogen for oxidation. : The substance that gives hydrogen or removes oxygen for reduction. : Symbolic representation of molecule of a substance. : Abbreviation of full name of an element. AMAZING FACTS Each time lightning strikes, some Ozone gas is produced, thus strengthening the Ozone Layer in the Earth's atmosphere. Hot water freezes faster than cold water (the Mpemba effect). 46 SCHOOL SECTION S.S.C. Marks : 30 CHAPTER 2 : MAGIC OF CHEMICAL REACTIONS Duration : 1 hr. SCIENCE Q.I 1. 2. 3. 4. Q.I 1. 2. 3. 4. Q.I 1. [A] Fill in the blanks : The chemical reaction during which hydrogen is lost is called as ....................... . The chemical reaction in which heat is evolved is called as ....................... reaction. Products are represented on ....................... . When copper powder is heated, ....................... is formed. 2 [B] Match the columns : Column A Gain of oxygen Digestion Iodine, Camphor NaOH + HCl NaCl + H2O 2 (a) (b) (c) (d) Column B Chemical change Oxidation Balanced equation Sublimatory substances [C] State whether True or False : Conversion of quick lime to slaked lime is an example of displacement reaction. Chemical change is a temporary change. 1 Q.I 1. 2. [D] Find odd man out : , (g), (l), =. Conversion of milk to curd, Rusting of iron, Digestion of food, Water turns into ice. 1 Q.II 1. [A] Give scientific reasons : (Any Two) Grills of doors and windows are always painted before they are used. Edible oil is not allowed to stand for a long time in an iron or tin container. Conversion of ice into water is a physical change. 4 [B] Distinguish between : Physical change and Chemical change. 2 2. 2. 3. Q.II 1. ... 2 ... Q.III 1. 2. 3. 4. [A] Balance the following chemical reaction : (Any Three) S + H2SO4 H2O + SO2 NH4Cl + Ca(OH)2 CaCl2 + H2O + NH3 Fe2O3 + CO Fe + CO2 ZnS + O2 ZnO + SO2 3 Q.III 1. 2. 3. [B] Identify the following reaction : Heat 2Hg + O 2HgO 2 CuSO4 + Fe FeSO4 + Cu CaO + H2O Ca(OH)2 + heat 3 Q.IV Explain the following chemical reactions with the help of balanced equation : (Any Three) 1. Calcium carbonate is heated. 2. Silver bromide is exposed to light. 3. Iron reacts with copper sulphate. 4. Silver nitrate reacts with sodium chloride solution. 6 Q.V 1. [A] Answer the following in detail : (Any One) What is the importance of a chemical equation? OR What information is conveyed by a chemical equation, give an example. State the neutralization. 4 [B] Define the following : Redox reaction. Corrosion. 2 2. Q.V 1. 2. Best Of Luck