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Class 10 chemical reactions and equations
- 1. Milk is leftat room temperature during summers. An iron tawa/pan/nail is left exposed to humid atmosphere. Grapes get fermented. Food is cooked. Food gets digested in our body. We respire.
- 2.
- 3. Activity 1.1 This Activityneeds the teacher’s assistance. It would be better if students wear eye protection. Clean a magnesium ribbon about 2 cm long by rubbing it with sandpaper. Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass as shown . Burn the magnesium ribbon keeping it as far as possible from your eyes. What do you observe?
- 4. Magnesium ismetal or non metal? Magnesium when it burn with oxygen ____ will form. Before using magnesium ribbon we want rub with sand paper why? What will happen when magnesium oxide is dissolved in water? Mgo is a metallic oxide or non-metallic oxide? Mgo is acidic in nature or basic in nature? What type of reaction will burning of magnesium ribbon belongs to?
- 5. Mg+O2MgO Why we wantto balance the equation? Balance the above equation: What is meant by combination reaction? Two reactant combine together to form a single product is called combination reaction.
- 6. Activity 1.2 Takelead nitrate solution in a test tube. Add potassium iodide solution to this. What do you observe? What is the symbol of lead? What is symbol for nitrate? What is the symbol of potassium iodide? Write the chemical formulae of lead nitrate and potassium iodide. Did you observe any colour? If yes why the colour formed.
- 7.
- 8. Zinc + Sulphuricacid Zinc Sulphate + Hydrogen Write the chemical equation for the above word equation. Need to write the chemical equation: Symbol Valency Chemical formulae What is meant by skeletal equation.
- 9. Fe + H2O→ Fe3O4 + H2 Balance the above chemical equation Follow the steps to balance the chemical equation.
- 10. Writing symbols ofphysical states: The gaseous, liquid, aqueous and solid state of reactants and products are represented by the notations (g),(l),(aq),(s). The reaction conditions, such as temperature, pressure, catalyst etc., for the reaction are indicated above and below the arrow in the equation
- 11. How youwill find whether the reaction takes place or not? A chemical reaction takes place can be identify by change in state Change in colour Evolution of a gas Change in temperature
- 12. TYPES OF CHEMICALREACTIONS 1.Combination reaction 2.Displacement reaction 3.Double Displacement reaction 4.Decomposition reaction 5.Redox reaction
- 13. Activity 1.4 Take asmall amount of calcium oxide quick lime in a beaker. Slowly add water to this. Touch the beaker as shown in Fig. 1.3.Do you feel any change in temperature? Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
- 14. COMBINATION REACTION: Inthis reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction. A solution of slaked lime produced by the reaction1.13 is used for white washing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3.
- 15. Examples of combinationreaction: (i)Burning of coal: (ii)Formation of water from H2(g) and O2(g) When two or more substance combine to form a single product the reactions are called combination reactions.
- 16. Types of reactionbased on heat:
- 17. Examples of exothermicreactions: (i)Burning of natural gas: We need energy to stay alive. We get this energy from the food we eat. During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration.
- 18. The decompositionof vegetable matter into compost is also an example of an exothermic reaction. Decomposition Reaction:
- 19. The singlereactant breaks down to give simpler products is called a decomposition reaction. Ferrous sulphate crystals (FeSO4, 7H2O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3),sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.
- 20. Decomposition ofcalcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition.
- 21. Decomposition Rxn: Theabove two decomposition take place by heating so we say this type of reaction as thermal decomposition.
- 22.
- 23. H2O(l)H2(g)+O2(g) 1.Why dilute sulphuricacid is added during electrolysis of water? 2. Which gas will be collected at anode and cathode? 3. Is the volume of the gas collected the same in both the test tube? The decomposition which takes place in presence of electric current is known as electrolytic decomposition.
- 24. Photolytic decomposition: Takeabout 2 g silver chloride in a china dish. What is its colour? Place this china dish in sunlight for some time (Fig. 1.7). Observe the colour of the silver chloride after some time. Silver chloride turns grey in sunlight to form silver metal. You will see that white silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light. The above reactions are used in black and white photography.
- 25. What form ofenergy is causing these decomposition reactions? We have seen that the decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants. Reactions in which energy is absorbed are known as endothermic reactions. Take about 2 g barium hydroxide in a test tube. Add 1 g of ammonium chloride and mix with the help of a glass rod. Touch the bottom of the test tube with your palm. What do you feel? Is this an exothermic or endothermic reaction?
- 26. 1.A solution ofa substance ‘X’ is used for white washing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water. 2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this
- 27.
- 28. Why doesthe iron nail become brownish in colour and the blue colour of copper sulphate solution fade?
- 29. In thisreaction, iron has displaced or removed another element, copper, from copper sulphate solution. This reaction is known as displacement reaction. Examples:
- 30. Double Displacement Reaction: Take about 3 mL of sodium sulphate solution in a test tube. In another test tube, take about 3 mL of barium chloride solution. Mix the two solutions (Fig. 1.9). What do you observe?
- 31. The white precipitateof BaSO4 is formed by the reaction of SO4-2 and Ba2+. The other product formed is sodium chloride which remains in the solution. Such reactions in which there is an exchange of ions between the reactants are called double displacement reaction.
- 32. Oxidation and Reduction: Heata china dish containing about 1 g copper powder ? What do you observe? The surface of copper powder becomes coated with black copper(II) oxide. Why has this black substance formed? This is because oxygen is added to copper and copper oxide is formed.
- 33. If hydrogen gasis passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained. If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced.
- 34. Examples: Inreaction (1.31) carbon is oxidised to CO and ZnO is reduced to Zn. In reaction (1.32) HCl is oxidised to Cl2 whereas MnO2 is reduced to MnCl2. From the above examples we can say that if a substance gains oxygen or loses hydrogen during a reaction, it is oxidised. If a substance loses oxygen or gains hydrogen during a reaction, it is reduced.
- 35. During thisreaction (1.29), the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidised. In other words, one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation- reduction reactions or redox reactions.
- 36. Corrosion: When ametal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the green coating on copper are other examples of corrosion.
- 37. Corrosion causesdamage to car bodies, bridges, iron railings, ships and to all objects made of metals, specially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron. You will learn more about corrosion.
- 38. Rancidity: When fatsand oils are oxidised, they become rancid and their smell and taste change. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Do you know that chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised ?