EXCERCISE (A) 1. (a) (b) 2. 3. (a) (b) (c) 4. (a) (b) 5. 6. 7. 8. Define A physical change A chemical change. Classify the following as a physical or chemical change: (a) Ripening of fruit, (b) (c) Charging a car battery, (d) (e) Manufacture of salt from sea (f) water, (g) Butter getting rancid, (h) (i) Growth of a tree, (j) (k) Making of dry ice from carbon (l) dioxide gas, (m) Boiling of water, (n) Liquefying air, Drying of wet clothes, Making of curd from milk, Heating of platinum wire, Rusting of iron, Bursting of water pipes in sever winter Burning of paper. Which of the following is not a physical change ? Freezing of water. Powdered sulphur when heated gently. Magnetising of a piece of iron. Give four characteristics of : A physical change A chemical change Differentiate between physical and chemical changes. Show that a physical change can easily be reversed. Explain which type of change occurs when water is electrolysed. When hydrogen burns in air, the change is chemical. Give two reason to support this assertion. 9. Explain why the heating of ammonium chloride can be understood as the combination of a physical as well as a chemical change. Give another example of the same type of change. 10. Give reasons to show that the following are chemical changes: (a) Burning of magnesium in air. (b) Adding of calcium of water. 11. Name a substance which on heating, leaves no residue behind. Give an equation. 12. How do the following help in burning about a chemical change ? (a) Pressure (b) Electricity (c) Light (d) Catalyst (e) Hear Give an example in each case. 13. What is the difference between dissolution of copper sulphate in water that of granulated zinc in dil. Hydrochloric acid ? 14. Explain why sublimation is regarded as a physical change and the slaking of lime a chemical change. 15. Freezing of water to ice and evaporation of water are both physical changes. Explain 16. Explain (a) (b) (c) 17. 18. (a) (b) (c) (d) When ammonium nitrate is dissolved in water contained in breaker, it becomes cold. When little sulphuric acid is added to water in a beaker, it becomes hot. Silver nitrate solution is kept in coloured reagent bottles in the laboratory. Give reasons why burning of a candle is both a physical and a chemical change. Complete the following statements by supplying the proper word or words: The process of a liquid changing into a solid is called ................... The temperature at which a solid changes into a liquid is called ......... The process of solid changing directly into a gas is called ....... A change which alters the composition of a substance is known as a ........ change. EXERCISE 5(B) 1. (a) Define chemical reactions. (b) Give the conditions necessary for a chemical change or reaction. 2. Define or explain the following terms: (a) (b) (c) 3. Chemical bond Effervescence Precipitate State the main characteristics of chemical reactions. Give at least one example in each case. 4. Define exothermic and endothermic changes. Give two examples in each case. 5. State the effect of an endothermic reaction and an exothermic reaction on the surroundings. 6. Give an example of reaction where the following are involved : 7. Define (a) Photochemical reaction (b) Electrochemical reaction Give on example in each case. 8. Give an example of each of the following chemical change (a) A photochemical reaction involving (i) Silver half (ii) (b) (i) (ii) (c) (d) Water A reaction involving Change of state Formation of precipitate An exothermic and endothermic reaction involving carbon as one of the reaction. A reaction where colour change is noticed. EXERCISE 5(C) 1. What is a chemical reaction? 2. 3. (a) (b) (c) 4. 5. 6. 7. 8. (c) 9. 10. 11. 12. 13. 14. (a) (b) (c) 15. (a) When hydrogen burns in oxygen, water is formed: when electricity is passed through water, hydrogen and oxygen are given out . Name the type of chemical change involved in the two cases. Complete the following statements by supplying proper words. The chemical change involving iron and hydrochloric acid illustrates a ............. reaction. In the type of reaction called ......... two compounds exchange their positive and negative radicals called .......... A catalyst either .......... or ........... the rate of a chemical change but itself remains ............... at the end of the reaction. Explain giving one simple example of each of the following chemical changes : (a) Double decomposition (b) Thermal dissociation (c) Electrolytic dissociation (d) displacement What is synthesis? What king of chemical reaction is synthesis? Support your answer by an example. Decomposition brought about by heat is known as thermal decomposition. What is the different between thermal dissociation and thermal decomposition? Define neutralisation reaction. Give three application of neutralisation reaction. (a) what do you understand by hydrolysis ? explain giving examples. What is decomposition ? support your answer by an example. Name the reaction in which rearrangement of atoms occurs. Give an example to illustrate it. Which type are the following reaction ? (a) 2 +2KBr2KCI+B2 (b) (c) (e) (g) (i) (k) 2HgO2HG+2 Ag3 +NaCIAgCI+Na3 22 222 +2 CuO+2 Cu+2 N4 CI3 +HCI (d) (f) (h) (j) + 4 4 + Pb2 +S2 4 2KCI3 2KCI+32 KN3 +2 4 HN3 CaC3 CaO+C2 Describe briefly the ionic concept of oxidation and reduction. Is it essential that oxidation and reduction must occur side by side in a chemical reaction ? explain. State, giving reasons whether underlined substances have been oxidised or reduced. PbO+COPb+C2 2 S+ 2 2HCI+S State whether the following conversations are oxidation or reductiuon: Pb2 +S2 4 (b) 16. (a) (b) 17. (a) (b) (c) (d) (e) (f) (g) 18. (a) (b) (c) (d) (e) (f) K + + − Give a chemical test for : an oxidising agent a reducing agent Give an example of each of the following types of reaction: An oxidation reaction involving removal of the electropositive element. A redox reaction involving a metallic oxide and a neutral gas as the only reactants. A catalytic reaction involving two gaseous reactants. A decomposition reaction which does not require heat i.e. other thanthermal decomposition. An oxidation reaction involving addition of the electronegative redical. A redox reaction involving two gases. A photochemical reaction involving a silver salt. Name An oxidising agent which does not contain oxygen. A substance which will oxidise concentrated HCI to chlorine. A substance which will reduce aqueous iron (III) ions to Iron (II) ions. A liquid which is an oxidising as well as reducing agent. A gas which is an oxidising as well as reducing agent. A solid which is an oxidising agent. EXERCISE 5(D) 1. (a) define burning (b) air is necessary for burning. Comment. 2. 3. 4. 5. 6. (a) (b) 7. (a) (b) 8. 9. (a) (b) 10. Why does magnesium gain weight on burning ? Name the products formed when candle burns in the air. Give are test for each product. What are the conditions for burning to take place? What do you understand by ignition temperature? Explain Why gun powder catches fire even in the absence of air. Water can be boiled in a paper cup. What are combustible and non-combustible substances ? Name two substances other than oxygen that support combustion. Define respiration. Give an experiment to show that respired air contains more carbons dioxide than atmosphere air. Compare the burning of carbon compounds with respiration. How is respiration similar to burning? Which gases are added to the air by : (a) (c) 11. Decay or fermentation Combustion (b) (d) Respiration Photosynthesis? (b) Respiration Which gases are removed from the air by : (a) (c) Photosynthesis Combustion 12. State two important processes which : (a) Release C2 into atmosphere (b) Remove C2 from atmosphere. 13. How does the balance of 2 and C2 is manufactured in nature ? 14. What will be the effect on : (a) Burning (b) Digestions (c) Metals, If nitrogen is absent in air. 15. What would be the effect on burning if the proportions of nitrogen and oxygen in the air were reversed? Other important questions Short answer type questions 1. State what would you observe and write equations for the reactions taking place when : Zinc carbonate is heated in a test rube and the test tube is allowed to cool ? 2. Which of the following are physical changes and which are chemical changes ? (a) (c) (e) (g) (i) (k) (m) 3. Freezing of water A platinum wire glows red hot in flame Heating ammonium chloride Onion sprouting Fermentation of flour Drying up plaster Magnetising a piece of iron. 5. 6. Dissolving sugar in water Switching on an electric lamp (f) (h) (j) (l) An iron nail gets rusted Melting of ghee Heating an electric iron Making curd from milk Give on example in each case : (a) (c) 4. (b) (d) Combination reaction Substitution reaction (b) (d) Decomposition reaction Double decomposition reaction. What is the difference between the dissolving copper sulphate in water and granulated zinc in dilute hydrochloric acid ? Respiration involves both physical and chemical changes. Justify. Give three applications of reactions of neutralisation. 7. Classify the following reactions : (a) (b) (c) (d) (e) (f) Zn+2 4 (dil) Zn 4 +2 (g) BaCI(aq)+ 2 4 (aq) Ba 4 (s)-2NaCI 2CO+2 2 C2 2KN3 2KN2 +2 3Fe+42 () Fe4 +42 22 22 () + 2 )) (g) 2KCI3 (h) (i) 2 + 2 2KCI+32 2HCI 8. CuO+2 + 2 In the above equations, by giving reasons. Explain which substance is : (a) Oxidised (b) Reducing (c) Oxidising agent (d) Reducing agent. 9. 10. 11. 12. 13. (a) (b) 14. 15. 16. 17. What do you understand by the term thermal dissociation? How is thermal dissociation different from thermal decomposition ? write two fully balanced equations for thermal dissociation reactions. What is energy of activation ? suppose your answer by one example. Define ‘energy change’ during a chemical reaction. Which type are the following reactions (a) (b) 4 N3 +HCI 2 + 22KCI+2 (c) (d) 2HgO2Hg+2 Fe+CuS2 Fe2 +Cu (e) (f) AgN3 + Ca3 CaO+C2 AgCI+Na N3 (g) (h) 2KCI3 2KCI+32 Pb2 +S2 PbS4 Give three examples in each case : Oxidising agents Reducing agents. What is a reversible reaction ? what is the most important condition for the reversible reaction to take place ? support your answer by a fully balanced chemical equation. What is the difference between precipitation reaction and neutralisation reaction ? which kind of chemical reactions belong to these reactions ? support your answer by one example each. What is analysis ? which kind of chemical reactions belong to analysis? Support your answer by an example. Indicate whether the given changes are physical or chemical changes. 18. 19. 20. (a) (b) (c) (d) 21. (a) (c) (e) (g) (i) (k) making of wine plucking of a fruit evaporation of water baking of cake glowing of a tube light burning of cooking gas (b) (d) (f) (h) (j) (l) (m) (o) (q) (s) (u) (w) burning of petrol drying of paint Rusting of iron ripeaning of iron breaking of glass pane fading of colour of a dyed cloth (n) (p) (r) (t) (v) (x) formation of dew production of biogas magnetisation of iron sublimation of dry ice making of ice-cream crystallisation of sugar from its saturated solution smoking of cigarette ringing of an electric bell dissociation of sugar in water butter turning rancid clotting of blood milk sours in hot and humid weather When we mix iron filing with sulphur and grind it, a physical change takes place. However, if we heat the mixture a chemical change takes place. Using the above sample give your differences between physical and chemical changes. When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical change involved in the two cases. Which is not a physical change in the following changes : Burning of a piece of magnesium wire in air. Freezing of water. Powdered sulphur when heated gently. Boiling of water. Give four characteristics of : (a) Rusting of iron (b) Digestion of food 22. A small piece of sodium is dropped into a beaker of water. Give two reasons why the reaction involves a chemical change. 23. Name four physical constant 24. Explain why sublimation is regarded as a physical change while the slaking of lime as a chemical change ? 25. Show that there is n no change in mass in a physical change. 26. What is a reactant and a product ? 27. What is atmospheric air ? 28. What do you know about the composition of air ? 29. What is the importance of dissolved air in water ? 30. Air contains nitrogen and oxygen. Name two other gases present in air. 31. Why are percentage of nitrogen in air different by volume and by mass ? 32. What happens what air is shaken with freshly boiled and cooled water ? 33. Show that oxygen is present in air. 34. What is the biological importance of dissolved oxygen and carbon dioxide in river water ? 35. A graduated tube containing some air stands inverted in water in a beaker. Now a substance X which is capable of reacting with oxygen is introduced . (a) Name the substance X. (b) If the tube originally contained 100cm3 of air, what would be the composition and volume of air above the water when all the oxygen had been remove ? 36. Name two substances formed during the combustion of candle. 37. Give the biological importance of nitrogen present in the air which we breath. 38. The diagram given below illustrates a method of determining the percentage of oxygen in air, using white phosphorus. After the reaction has ceased the volume of the gas was found after levelling. Answer the following questions : (a) Name the main gas left behind after the experiment. (b) What is the purpose of phosphorus ? (c) What is the approximate percentage of oxygen in the air ? 39. When a piece of magnesium is burnt in air, its weight increase whereas when a candle burns in air its weight decreases. Explain the observation. 40. Explain why the fish and water plants can survive in river water, but not in a stopered jar containing distilled water. 41. What are polluting gases ? what harm do they cause ? 42. By volume, which of the following is the amount of carbon dioxide in pure air ? (a) 0.03% (b) 0.93% (c) 78.09% 43. What is the ratio of nitrogen and oxygen in air ? 44. Which room will have pure air : (a) Window and ventilators opened room. (b) Windows and ventilators close room. 45. Which of the following is produced by burning organic substances : (a) Oxygen (b) carbon dioxide (c) nitrogen. 46. Constituents of air can be separated by : (a) Filtration (c) crystallisation (b) Liquefaction (d) sublimation 47. Rewirte the following sentences after necessary corrections : (a) Nitrogen supports combustion and oxygen controls combustion. (b) During respiration we use nitrogen and give out hydrogen and oxygen. (c) Air contains 1/5 part of its volume as nitrogen and 4/5 part as oxygen. (d) Atmosphere air contains more carbon dioxide than exhaled air. 48. The table give below gives a summary of the element. You are required to study this table and answer the questions that follow : 49. How is oxygen separated from air ? 50. When 2g of Mg is burnt in air the weight of resultant white powder is much more than 2g, why ? 51. Name the principle oxide with each of the following : 52. Describe what do you observe and write equation for the actions taking place when : (a) Potassium nitrate is heated strongly in a test tube. (b) Write an equation for reaction taking place when mercuric oxide is headted. 53. Fill in the blanks : (a) The air of industrial town has more ........... than the air of open country. (b) When the liquid air is allowed to evaporate ........ which has lower boiling point evaporate leaving behind ............. . (c) The substances which can be in air are called ........ while substances which cannot burn in air are known as .............. . 54. How is air purified by plants ? 55. Air contains nitrogen and oxygen. Name the two other gases present in air. 56. When air is passed through water for sometime, the percentage of oxygen in water increase. Explain. 57. What is the significance of dissolved air in water ? 58. Name four substances capable of absorbing water vapours. 59. Why does anhydrous calcium chloride become sticky when exposed to air ? 60. Why does gun powder burn without air upon heating strongly ? 61. Name the inert gases present in air. Why are they so called ? 62. Why proportion of nitrogen in both inspired air and expired air remains the same ? 63. Why does proportion of carbon dioxide in air remains almost the same although a large amount of fuel burns both in home and factories ? 64. Why does mist appear on the surface of a glass plate when hold over the flame of a burning candle ? 65. How do plants help in checking air pollution ? 66. Name the gases which are added to air by : (a) Decay of fermentation (b) Respiration (c) Combustion (d) Oxygen. 67. Name two major constituents of air other than oxygen and nitrogen . describe how each of these can be identified. 68.