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Comprehensive CHEMISTRY–XI Value Based Questions CHAPTER 2 1. Radiowaves are used for broadcasting radio signals whereas microwaves are used for telecommunication. Both of these are electromagnetic waves. Answer the following questions: (i) Which radio station broadcasts at a longer wavelength—an FM radio station or an AM radio station. (ii) Out of FM radiowaves and microwaves which are more energetic and can be harmful to human beings. (iii) An FM radio station broadcasts at a frequency of 103.1 MHz. What is the wavelength of these radiowaves in meters? 2. By studying the spectrum of light coming from some distant star, it becomes possible to identify the elements present on the star. Answer the following questions: (i) How does a scientist identify the elements present on the star by studying the spectrum of light from the star? (ii) What are the wavelengths of the two characteristic lines in the visible region in the atomic spectrum of sodium? CHAPTER 3 3. Most of the elements that exist in nature are metals. The most abundant metal in the earth’s crust belongs to p-block while the second most abundant metal belongs to d-block. The lightest metal that has sufficient mechanical strength to be used in construction, belongs to s-block. Metals are important natural resource and should be used judiciously. What is the group number and period of the following elements? (i) The most abundant metal. (ii) The second most abundant metal. (iii) The lightest metal that is used in construction. CHAPTER 6 4. About 75–80% of the world’s total requirement of energy is in the form of heat energy. We meet this requirement mostly from the combustion of fossil fuels. Slowly and gradually we are getting into the grip of energy crisis. Answer the following questions: (i) Can we convert one form of energy into another? Name the law you rely upon while answer in this question. (ii) If there is conversation of energy in all chemical and physical processes, why are we facing energy crisis? Explain. CHAPTER 7A 5. Nitric oxide catalyses decomposition of ozone in the upper atmosphere. Nitric oxide is an air pollutant formed the reaction of N2 and O2 from air at high temperatures such as combustion temperatures in automobile and airplane engines. Besides NO, the exhaust gases from automobile engines also contain CO and unburnt hydrocarbons as pollutants. Modern automobile engines are fitted with catalytic converters. In the petrol engines which are fitted with catalytic converters lead-free petrol is used. Answer the following questions: (i) What is the role of catalytic converter in the automobiles? (ii) Name the major pollutants present in the exhaust gases of automobiles. (iii) Which pollutant catalyses decomposition of ozone into oxygen? (iv) How does ozone in the upper atmosphere help plants and animals on earth? CHAPTER 7B 6. Carbonic acid solutions play an important role in environment chemistry. Carbon dioxide gas Comprehensive 2 released into the atmosphere, by burning fossil fuels and forest fires, dissolves in rain, rivers, lakes, etc. making them acidic. Answer the following questions: (i) What is the molecular formula of carbonic acid? (ii) Is carbonic acid monoprotic or a polyprotic acid? (iii) Is carbonic acid a weak acid or a strong acid? (iv) Give chemical equation representing ionization of carbonic acid. 7. Natural rainwater is slightly acidic and has a pH of about 5.7. This is due to presence of carbonic acid in rainwater. However due to the presence of pollutants such as SO2 and NO2 in the air some rainwater has a pH as low as 1.0. SO2 and NO2 are generated as by products of industrial energy production by roasting of sulphide ores and by combustion of natural gas, petrol, diesel etc. The high acidity of rainwater has devastating effects on environment. Answer the following questions: (i) Give chemical equations for the formation of acids by dissolution of CO2, SO2 and NO2 in water. (ii) Rainwater in an industrial area has a pH of 1.5. Calculate [H3O+] and [OH–] in this rainwater. (iii) List any two adverse effects of highly acidic rainwater on environment. CHAPTER 9 8. Certain compound ‘X’ contains hydrogen and oxygen elements. It covers about 75% of earth’s surface. It is also a major part of all living organisms. Human body contains about 65% of X. A unique feature of X is that ‘X’ in solid state floats over ‘X’ in liquid state. Answer the following questions: (i) What is chemical constitution of X? (ii) What ecological significance is associated with the fact that X(s) floats of X(l)? (iii) Only a very small percentage (2.5%) of total ‘X’ on earth is available for human consumption. Why? 9. In the school laboratory, the chemistry teacher instructed the laboratory attendents to store a CHEMISTRY—XI liquid substance of hydrogen and oxygen element in brown bottles in dark room. He also told to add some area to it and keep it free from dust. The substance can act as oxidising agent and reducing agent both in acidic and alkaline media. Answer the following questions: (i) Name the liquid substance. (ii) Give its structure. (iii) What value does it carry in pollution control of domestic and industrial effluents? CHAPTER 10 10. Potassium metal reacts with excess oxygen to form potassium superoxide, KO2. KO2 is used in space capsules, submarines and breathing masks because it removes CO2 and at the same time produces oxygen. Answer the following questions: (i) Give chemical equations for the reaction of KO2 with CO2 and with water. (ii) What is the oxidation state of oxygen in KO2? (iii) Give electron dot structure of superoxide ion. CHAPTER 13 11. BHT is an antioxidant and is used as a food preservative. It is a mixture of structural isomers of butylated hydroxytoluenes. The major component in BHT is 2, 6-di-tert-butyl-4methylphenol. It is prepared industrially by the reaction of p-methylphenol and 2-methylpropene, in the presence of acid, using methanol as solvent. Answer the following questions: (i) What is the structural formula of the major component in BHT? (ii) How do you explain the formation of this component by reaction of p-methylphenol and 2-methylpropene in the presence of acid? (iii) Write the mechanism of the reaction involved. [Hint: OH group is very strong activating group where –CH3 group is mild activating group.] 12. Combustion of carbon containing compounds with limited supply of oxygen yields polycyclic aromatic hydrocarbons which are carcinogenic as well as mutagenic. Some polycyclic aromatic hydrocarbons have been isolated from tobacco smoke. 3 VALUE BASED QUESTIONS Answer the following questions: (i) Give examples of any two polycyclic aromatic hydrocarbons. (ii) A polycyclic aromatic hydrocarbon has molecular formula C10H8. Draw the various possible resonating structure of this compound. (iii) Explain why tobacco smoking is injurious to health? CHAPTER 14 13. Drycleaners in your area frequently use tetrachloroethane for the purpose of drycleaning. They were advised to use liquefied carbon dioxide with suitable detergent as an alternative solvent. Answer the following questions: (i) What type of harm to the environment can be prevented by avoiding the use of tetrachloroethane? (ii) Will the use of liquefied carbon dioxide and detergent be completely safe from the point of view of pollution? Comment. 14. During the educational trip, a group of students visited a village having a beautiful lake. The students collected some plants samples and noticed that some villagers are washing clothes around the lake. They also observed the dumping of waste material from the houses into the lake at certain points. After few years, the students happened to visit the same village again. They were shocked to find the green cover over the lake water which was unusable and badly stinking. Answer the following questions: (i) What is the name of green cover over lake water? (ii) Why the lake water had developed bad smell? (iii) How this situation could have been avoided? Give your views. 15. On visit to your friend’s farmhouse you find that, the farmer uses excessive pesticides on his farm. The produce of his farm was being used as a food for rearing fishes. Your friend was shocked to know that the fish of his farm were not fit for human consumption. Answer the following questions: (i) What can be the possible reason for fish to be declared unfit as human food? (ii) How can you explain your friend the cause of this situation to develop? (iii) What suggestion you will give for future? HINTS/ANSWERS N Chapter 2 N 1. (i) AM Radio station broadcasts at longer wavelength. (ii) Microwaves are more energetic as they have smaller wavelengths. Their photons have more energy. Microwaves can be harmful to human beings. (iii) c = νλ c 3 × 108 m s−1 = = 2.91 m. ν 103.1 × 106 s−1 2. (i) Each element has characteristic line spectrum. By comparing the lines present in the spectrum of light from the star with those of the atomic spectra of elements a scientist identifies the elements present on the star. The presence of element helium on the sun, was detected by studying the spectrum of light from the sun. (ii) 589.2 nm and 589.6 nm. These wavelengths are responsible for the golden yellow light emitted by sodium vapour lamps. N Chapter 3 N 3. λ= (i) The most abundant metal is aluminium. It belongs to group-13 and period-3. (ii) The second most abundant metal is iron. It belongs to group-8 and period-4. (iii) The lightest metal that is used in construction is magnesium. It belongs to group-2 and period-3. N Chapter 6 N 4. (i) Conversion of one form of energy into another form is possible as per the statement of first law of thermodynamics. However, complete conversion of heat into work is not possible. No heat engine can have 100% efficiency. (ii) The energy crisis is not because of nonvalidity of first law of thermodynamics but it is because of drying up of natural sources of fossil fuels which are frequently used for Comprehensive 4 generating heat energy. In combustion of fossil fuels we convert chemical energy into heat energy which is a random form energy and cannot be completely converted into work energy. N Chapter 7A N (i) The catalytic converter in automobiles converts NO to N2 and O2, CO to CO2, and hydrocarbons to CO2 and H2O. (ii) Nitric oxide (NO), carbon monoxide (CO) and hydrocarbons. (iii) Nitric oxide catalyses decomposition of ozone into oxygen. (iv) It protects plants and animals from the harmful ultraviolet radiations, present in the sun rays, by absorbing these radiations. N Chapter 7B N 6. 9. H2CO3 It is a diprotic (polyprotic) acid. Carbonic acid is a weak acid. H2CO3 (aq) H+ (aq) + HCO–3 (aq) – HCO 3 (aq) H+ (aq) + CO2– 3 (aq). 7. (i) CO2(g) + H2O(l) → H2CO3(aq) SO2(g) + H2O(l) → H2SO3(aq) 2NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq) (ii) pH = 1.50 –log[H3O+] = pH = 1.50 log[H3O+] = –1.50 = 2.50 [H3O+] = 3.16 × 10–2 M (ii) (iii) N Chapter 10 N 10. (i) (ii) (iii) (iv) [OH–] = Kw 1 × 10 −14 = [H3O+ ] 3.162 × 10 −2 = 3.16 × 10–13 M (iii) (a) It corrodes the monuments and buildings which are made up of marble. (b) It promotes rusting. (c) It harms the leaves of plants. (i) frozen water does not sink to the bottom but keeps floating at the surface. This provides thermal insulation to the water below it. Most of the surface water is locked up in polar ice caps, glaciers or under the ground and is not readily available. The liquid substance is hydrogen peroxide having formula H2O2. It has open book like structure (Refer section 9.9, Fig. 9.9(a) and 9.9(b) for details in textbook). The knowledge of oxidative ability of H2O2 is being used, now a days in pollution control. It is used in treatment of domestic and industrial waste, oxidation of cyanides and restoration of aerobic conditions to sewage waste. (i) 4KO2(s) + 2CO2(g) → 2K2CO3(s) + 3O2(g) KO2(s) + H2O(l) → KOH(aq) + H2O2(aq) + O2(g) (ii) –1/2 (iii) :O : O: : : . : 5. (iii) N Chapter 13 N 11. (i) H3 C H3 C CH3 (i) X is water with chemical formula H2O. In solid state it exists as ice which has density lower than that of water. (ii) Ice being lighter floats over the surface of water. This property is a boon for survival of aquatic animals during winter months because when upper of sea water freezes, the OH C CH3 CH3 C CH3 CH3 (ii) —OH group is very strong activating and ortho-para directing group whereas —CH3 is a mild activating group. Therefore, electrophilic substitution mainly takes place at positions ortho to —OH group (para position is occupied by —CH3). (iii) (a) CH3—C N Chapter 9 N 8. CHEMISTRY—XI + CH2 + H + CH3—C—CH3 CH3 CH3 OH + (b) + CH3—C—CH3 CH3 CH3 OH CH3 CH3 H C + CH3 CH3 5 VALUE BASED QUESTIONS (c) OH CH3CH 3 H C CH3 + –H OH CH3 CH3 C CH3 + CH3 CH3 Another similar attack of tert-butyl carbocation at the second ortho position results in the formation of 2,6-di-tert-butyl4-methylphenol. 12. (i) Anthracene (ii) Phenanthrene (iii) Because tobacco smoke contains many polycyclic aromatic hydrocarbons which are carcinogenic and mutagenic. N Chapter 14 N 13. (i) Exessive use of chlorofluorocarbon compounds become the cause of ozone depletion in the stratosphere. Thus, avoiding indiscriminate use of such compounds can save us from the harmful effects of ozone layer depletion. (ii) Use of liquified carbon dioxide solvent is not absolutely safe. The exessive concentration of CO2 in the atmosphere leads to greenhouse effect. 14. (i) The green cover over polluted water is algae. (ii) When too much of organic waste is dumped into water, most of the dissolved oxygen is used up. As a result oxygen dependent aquatic life die. The anaerobic bacteria (which donot require oxygen) begin to break down the organic waste and thus produce chemicals with foul smell. (iii) This situation could have been avoided by keeping the lake water clean and not allowing washing of clothes or dumping of household waste in lake water. 15. (i) The fishes were unfit for human consumption because of toxins present in their bodies. (ii) The fish were fed by the produce of farm where too much of pesticides and herbicides were used which contains non-biodegradable toxic chemicals. Gradually, these toxins get transferred from the farm produce to the fish in the water body making them unfit for human consumption. (iii) This situation could be avoided by stopping the exessive and indescriminate use of pesticides and adopting other eco-friendly means. Also the water bodies should be aerated and cleaned from time to time.