33 Environmental Chemistry Objective Questions I (Only one correct option) 1. The primary pollutant that leads to photochemical smog is (a) acrolein (c) ozone (b) nitrogen oxides (d) sulphur dioxide 2. The correct set of species responsible for the photochemical smog is (a) (b) (c) (d) N2 , NO2 and hydrocarbons CO2 , NO2 , SO2 and hydrocarbons NO, NO2 , O3 and hydrocarbons N2 , O2 , O3 and hydrocarbons 3. Air pollution that occurs in sunlight is (a) acid rain (c) fog (b) oxidising smog (d) reducing smog 4. The regions of the atmosphere, where clouds form and where we live, respectively, are (a) stratosphere and stratosphere (b) troposphere and troposphere (c) troposphere and stratosphere (d) stratosphere and troposphere (b) mesosphere (d) troposphere 6. Excessive release of CO2 into the atmosphere results in (b) depletion of ozone (d) global warming 7. The maximum prescribed concentration of copper in drinking water is (a) 5 ppm (c) 0.05 ppm (a) Restricting the use of vehicles (b) Avoiding the use of floodlighted facilities (c) Setting up compost tin in gardens (d) Using plastic bags 10. The upper stratosphere consisting of the ozone layer protects us from the sun’s radiation that falls in the wavelength region of (a) 600 - 750 nm (c) 0.8 - 15 . nm (b) 400 - 550 nm (d) 200 - 315 nm 11. The compound that is not a common component of photochemical smog is (a) CF2Cl 2 (c) CH2 == CHCHO (b) H3 C ¾ C ¾ OONO2 ½½ O (d) O3 respectively, are sea level is called as (a) formation of smog (c) polar vortex human being to protect our environment? 12. Water samples with BOD values of 4 ppm and 18 ppm, 5. The layer of atmosphere between 10 km to 50 km above the (a) stratosphere (c) thermosphere 9. Which is wrong with respect to our responsibility as a (b) 0.5 ppm (d) 3 ppm 8. Assertion (A) Ozone is destroyed by CFCs in the upper stratosphere. Reason (R) Ozone holes increase the amount of UV radiation reaching the earth. (a) Assertion and Reason are incorrect. (b) Assertion and Reason are both correct and the Reason is the correct explanation for the Assertion. (c) Assertion and Reason are correct, but the Reason is not the explanation for the Assertion. (d) Assertion is false, but the Reason is correct. (a) clean and clean (b) highly polluted and clean (c) highly polluted and highly polluted (d) clean and highly polluted 13. The molecule that has minimum/no role in the formation of photochemical smog, is (a) N2 (c) NO (b) CH2 == O (d) O3 14. Taj Mahal is being slowly disfigured and discoloured. This is primarily due to (a) water pollution (c) global warming (b) soil pollution (d) acid rain 15. The higher concentration of which gas in air can cause stiffness of flower buds? (a) SO2 (c) CO2 (b) CO (d) NO2 16. Peroxyacetyl nitrate (PAN), an eye irritant is produced by (a) (b) (c) (d) organic waste acid rain classical smog photochemical smog Environmental Chemistry 17. The concentration of dissolved oxygen (DO) in cold water can go upto (a) 14 ppm (c) 8 ppm (b) 10 ppm (d) 16 ppm 20. The pH of rain water, is approximately 18. The reaction that is not involved in the ozone layer depletion mechanism in the stratosphere is (a) CH4 + 2O3 ¾® 3CH2 == O + 3H2O · · (b) 6.5 (d) 7.0 (a) > 50 ppm nitrate (c) > 50 ppm lead · hn (c) HOCl(g ) ¾® OH(g ) + Cl(g ) hn (a) 7.5 (c) 5.6 21. The condition for methemoglobinemia by drinking water is · (b) Cl O(g ) + O(g ) ¾® C l(g ) + O2 (g ) · (b) A is suitable for drinking, wherease B is not (c) Both A and B are suitable for drinking (d) B is more polluted than A · (d) CF2Cl 2 (g ) ¾® Cl(g ) + CF2Cl(g ) (b) > 50 ppm chloride (d) > 100 ppm sulphate 22. A water sample has ppm level concentration of the 19. Water filled in two glasses A and B have BOD values of 10 and 20, respectively. The correct statement regarding them, is (a) A is more polluted than B following metals: Fe = 0.2; Mn = 5.0 ; Cu = 3.0; Zn = 5.0. The metal that makes the water sample unsuitable for drinking is (a) Cu (c) Mn (b) Fe (d) Zn Answers 1. (b) 5. (a) 9. (d) 2. (c) 6. (d) 10. (d) 3. (b) 7. (d) 11. (a) 4. (b) 8. (c) 12. (d) 13. (a) 14. (d) 15. (a) 16. (d) 17. (b) 18. (a) 19. (d) 20. (c) 21. (a) 22. (c) Hints & Solutions 1. The primary pollutant that leads to photochemical smog is nitrogen oxides. Burning of fossil fuels such as petrol and diesel in automobiles, reaction between nitrogen and oxygen and other such reactions result in a variety of pollutants, two main of which are hydrocarbons (unburnt fuel) and nitric oxide (NO). In petrol and ¾diesel ¾¾ ¾¾® engines N2(g ) + O2 (g ) 3CH4 (g ) (Unburnt hydrocarbon) NO2(g ) + O2 (g ) Brown gas (in high concentration form haze) + 2O3 (g ) ¾® 3CH2 == O(g ) Formaldehyde + CH2 == CHCH == O+ H2O 2NO(g ) Acrolein When the concentration of these pollutants is sufficiently high, a chain reaction initiate because of the interaction of sunlight with oxides of nitrogen. 2NO(g ) + O2 (g ) ¾ ¾ ¾® 2NO2 (g ) Sunlight hn NO2(g ) ¾¾ ® NO(g ) + [ O] Nascent oxygen O3 (g ) + NO(g ) ¾® NO2 (g ) + O2 (g ) Brown gas 2. The correct set of species responsible for the photochemical smog is NO, NO2, O3 and hydrocarbons. Photochemical smog appears in warm, dry and sunny climate which are obtained by the action of sunlight on unsaturated hydrocarbons and nitrogen oxides. Following reactions are involved during the formation of photochemical smog. (i) N2 (g ) + O2 (g ) ¾¾¾® 2NO(g ) (Originates from burning of fossil fuels) 3. In sunlight oxidising smog or photochemical smog or Los-Angeles smog is formed. This smog is brown in colour. It occurs in warm, dry and sunny climate. In presence of sunlight, NOx (N-oxides), O2 and unburnt hydrocarbons of air combine to produce photochemical smog which mainly contains peroxyacetyl O || nitrate (PAN). CH3 ¾ C ¾ O ¾ O ¾ NO2 (PAN) 4. The lowest region of atmosphere is troposphere which extends upto the height of 10 km (approx) from sea level. We live in the tropospheric region. It contains air, water vapour and dust which can form clouds with the help of strong air movement. Above the troposphere, stratospheric region extends upto 50 km from sea level. It contains mainly N2 , O2 , O3 and little water vapour. O3 in the stratosphere absorbs 99.5% of the sun’s harmful UV raditions and thus protects the lives on the earth. 5. The atmosphere between the heights 10 to 50 km above the sea Sunlight (ii) 2NO(g ) + O2 (g ) ¾¾¾® 2NO2 (g ) hn NO2 (g ) ¾¾¾® NO(g ) + [ O ] Nascent oxygen (iii) O (g ) + O2 (g ) O3 (g ) + NO(g ) ¾® - O (g ) 3 Reacts rapidly with NO level is stratosphere. Atmosphere is not of the same thickness at heights. 6. The effect of release of CO2 gas into atmosphere is global warming. Environmental Chemistry 7. According to W.H.O. and US environmental protection agency 12. The amount of oxygen required by bacteria to break down the guidelines, maximum allowable concentration of metals in drinking water are as follows : organic matter present in a certain value of a sample of water is called biochemical oxygen demand (BOD). The amount of BOD in the water is a measure of the amount of organic material in the water, in terms of how much oxygen will be required to break it down biologically. Clean water would have BOD value of less than 5ppm whereas highly polluted water would have BOD value of 17 ppm or more. Metal Maximum concentration (ppm or mg dm-3) Cd 0.005 Mn 0.05 (option-c) Al 0.2 Fe 0.2 Cu 3.0 (option-d) Zn 5.0 (option-a) BOD value of clean water = 4 ppm BOD value of highly polluted water = 18 ppm 13. N2 molecule has minimum role in the formation of photochemical 8. Ozone is destroyed by CFCs in the upper stratosphere. These compounds ultimately reach the stratosphere where they get broken down by powerful UV radiations and release chlorine free radical. The chlorine free radicals react with ozone and cause its depletion by converting it into chlorine monoxide radical and molecular oxygen. hn · CF2Cl2 (g ) ¾¾® Cl (g ) + C F2Cl(g ) hn · CFCl3 (g ) ¾¾® CFCl2 (g ) + C l(g ) · · C l(g ) + O3 (g ) ¾¾® Cl O(g ) + O2 (g ) Ozone holes increase the amount of UV radiation reaching the earth. These radiations can cause skin cancer, sunburns, ageing of skin. smog. While CH2 == O, O3 and NO has major role. When fossil fuels are burnt, a variety of pollutants are emitted. Two of them are hydrocarbons (unburnt) and NO. When these pollutants build upto high levels, a chain reaction occurs from their interaction with sunlight. The reactions involved in the formation of photochemical smog are as follows: hn NO2( g ) ¾¾ ® NO( g )+ O( g ) O( g )+ O2( g ) O3( g ) NO( g ) + O3 ( g ) ¾® NO2( g ) + O2( g ) d O 3 reats with unburnt hydrocarbons to produce chemicals such as formaldehyde, acrolein and PAN. 3CH4 + 2O3 ¾® 3CH2 == O + 3H2O + CH2 ==CCH == O + CH3 C OONO2 ½½ O (PAN) 9. Using plastic bags is wrong with respect to responsibility as a 14. Acid rain (pH = 3.5 - 5.6) constitutes strong acids like HNO3, human being to protect our environment. Plastic bags are non-biodegradable in nature. It remains in the environment as such and does not degraded by bacteria. If it is not disposed properly then it may lead serious threat to the environment. The activities that can be used to protect our environment are as follows: H2SO4 and H2SO3 which slowly react with marble (CaCO3 ) of Taj Mahal and make it disfigured and discoloured. Here, CaCO3 (marble) gets dissolved in acids. l l l Restricting the use of vehicles. Avoiding the use of flood lighted facilities. Setting up compost tin in gardens. 10. Sun emits UV-radiations, which according to following EM categorisation have the wavelength range from 1 nm to 400 nm. Type Wavelength range Radio wave > 0.1 m Microwave 0.1 m to 1 mm Infrared wave 1 mm to 700 nm Visible rays 700 nm to 400 nm Ultraviolet rays 400 nm to 1 nm -3 X-rays 1 nm to 10 Gamma rays < 10- 3 nm nm Thus, option (d) with 200-315 nm range is the correct option. 11. Freons or CFCs or chlorofluoro carbons, i.e. CF2Cl2 is not the common component of photochemical smog. This smog is produced as the result of tropospheric pollution while freons are the components of stratospheric pollution. These are infact considered as the major cause of ozone layer depletion. 2 H Å (aq) CaCO3 (s) ¾¾¾® Ca 2 + (aq) + H2O(l ) + CO2 (g ) (Acid rain) 15. Organic pigments (colourents) present in flower buds retain their colour in the oxidised form of the pigment as their nature is itself oxidising in nature. When they comes in contact with moist SO2 (acid rain) of higher concentration, they get decoloured and stiff. SO2 + H2O ¾® H2SO4 H2SO4 ¾® H+ + HSO-4 HSO-4 ¾® H+ + SO24 Due to the release of H+ ion (acid), the flower get decoloured and stiff. As a result, flower eventually falls off from plants. 16. Molecular formula of peroxyacetyl nitrate (PAN) is O ½½ CH3 ¾ C ¾ O ¾ O ¾ NO2. It is a secondary pollutant. It is present in photochemical smog (oxidising or Los Angeles smog). PAN is a powerful lachrymator or tear producer and it also causes breathing troubles. 17. Dissolved oxygen (DO) is the oxygen dissolved in water either from atmosphere or by photosynthesis. The lower the concentration of DO in a water sample, the more polluted is the water sample. Environmental Chemistry The concentration range of dissolved oxygen (DO) in cold water reaches upto 10 ppm, but that in normal water (at room temperature) is within 5 ppm. 18. CH4 is not present in the stratosphere and also it cannot diffuse or escape into the stratosphere like freon-12 (CF2Cl2) from the atmosphere. In the stratosphere, ozone layer depletion take place mainly by chlorofluorocarbons (CFCs) like CF2Cl2 and the mechanism of ozone layer depletion can be shown as: · hn · (i) CF2Cl2(g ) ¾¾® C l(g ) + C F2Cl(g ) [Option, (d)] · (ii) C l(g) + O3 (g ) ¾® ClO· (g ) + O2 (iii) ClO· (g ) + O(g ) ¾® Cl· (g ) + O2 (g ) [Option (b)] · (iv) C l(g ) + H2O(g ) ¾® HOCl(g ) + H· (g ) [Present in the stratosphere] · sample of water. Clean water or drinking water has a BOD value < 5 ppm. So, water filled with A, BOD = 10 ppm is polluted and water filled with B, BOD = 20 ppm, is also polluted. But, B is more polluted than A. 20. In clean air, rain water picks up some acidic oxides like CO 2 and SO 2 (obtained from volcanic eruptions). These substance make the rain slightly acidic (pH = 5.6 - 6). 21. According to EEC (European Environment Commission), excess of NO -3 (> 50 ppm) in drinking water may lead to methemoglobinemia (‘Blue baby syndrome’). It also may cause stomach-cancer. 22. For drinking water, the maximum recommended levels of some metals, set by European Environment Commission (EEC) is Metal Max. concentration in ppm (v) HOCl(g ) ¾¾® OH(g ) + Cl· (g ) [Option (c)] Zn 5 Þ One Cl· can destroy or deplete 105 O3 molecules. Mn 0.05 Fe 0.2 Cu 3 hn As (i) reaction is involved in the formation of photochemical smog, not in ozone layer depletion. So option (a) is correct. 19. BOD is defined as the amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a As the concentration of Mn in the given water sample is more than the recommended concentration. Thus, it makes water unsuitable for drinking.