Gujarat Board GSEB Textbook Solutions Class 11 Chemistry Chapter 14 Environmental Chemistry Textbook Questions and Answers.
Gujarat Board Textbook Solutions Class 11 Chemistry Chapter 14 Environmental Chemistry
GSEB Class 11 Chemistry Environmental Chemistry Text Book Questions and Answers
Define environmental chemistry.
Environmental chemistry deals with the study of the origin, transport, reactions, effects and fates of chemical species in the environment.
Explain tropospheric pollution in 100 words.
Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in air. The following are the major gaseous and particulate pollutants present in the troposphere.
Gaseous air pollutants : These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.
Particulate pollutants: These are dust, mist, fumes, smoke, smog etc.
1. Gaseous air pollutants –
(a) Oxides of sulphur : Oxides of sulphur are produced when sulphur containing fossil fuel is burnt. SO2 gas is poisonous to both animals and plants.
(b) Oxides of Nitrogen : Dinitrogen and dioxygen are the main constituents of air. At high altitudes when lightening strikes, they combine to form oxides of nitrogen
(c) Hydrocarbons : They are formed due to incomplete combustion of fuel used in automobiles and are carcinogenic.
(d) Oxides of carbon : CO is one of the most serious air pollutant. CO is mainly released in the air due to incomplete combustion of carbonium in the form of coal, fire wood, petrol etc. CO2 is released into the atmosphere by respiration and burning of fossil fuels. It is emitted during volcanic eruptions and cement plants.
Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?
The presence of CO reduces the amount of heomoglobin of the red blood corpuscles (RBCs) about 300 times more easily than oxygen to form carboxyhaemoglobin reversibly as follows :
CO + Hb ⇌ HbCO
Thus it is not able to combine with oxygen to form oxyhaemoglobin and transport of oxygen to different body cells cannot take place. It is so poisonons that within half and hour, 1300 ppm is fatal.
List gases which are responsible for greenhouse effect?
Carbon dioxide is the major contributor to global warming or green house effect. In addition to CO2 methane (CH4, ozone (O3), chloroflurocarbon compounds (CFCs) oxides,nitrogen and water vapour. They add to the heating of the atmosphere which causes global warming.
Statues and monuments in India are affected by acid rain. How?
Acid rain is the rain water containing sulphuric acid and nitric acid (along with small amount of hydrochloric acid) and has a pH of 4-5. Acid rain causes excessive damage to statues and monuments specially those made of marble, lime stone, slate, mortar etc. For example Taj Mahal at Agra made of marble (CaCO3) is being attacked by acid rain.
CaCO3 + H2SO4 → CaSO4 + CO2 + H2O
As a result, marble is being corroded and eaten up causing pitting and ‘discolouring & thus making it lustreless.
What is smog? How is classical smog different from photochemical smogs?
The word smog is derived from smoke and fog. This is the best known example of air pollution that occurs in many cities throughout the world. There are two types of smogs :
(a) Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixtuie and so it is also called as reducing smog.
(b) Photochemical smog occurs in warm, dry and sunny climate. The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog.
Write down the reactions involved during the formation of photochemical smog.
When fossil fuels are burnt, a variety of pollutants are emitted into the earth’s troposphere. Two of the pollutants that are emitted are hydrocarbons (unburnt fuels) and nitric oxide (NO). When these pollutants build up to sufficiently high levels, a chain reaction occurs from their interaction with sunlight in which NO is converted to nitrogen dioxide (NO2). This NO2 absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom.
Oxygen atoms are very reactive and can combine with the O2 of the air to produce ozone.
O(g) + O2(g) → O3(g) … (ii)
The ozone formed in the above reaction (ii) reacts rapidly with the NO(g) formed in reaction (i) to regenerate NO2. NO2 is a brown gas and at sufficiently high levels can contribute to haze.
NO(g) + O3(g) → NO2(g) + O2(g) … (iii)
Ozone is a toxic gas and both NO2 andO3 are strong oxidising agents and can react with the unburnt hydrocarbons in the polluted air to produce chemicals such us formaldehyde (HCHO), acrolein (CH2 = CH CHO) and peroxyacetyl nitrate (PAN).
What are the harmful effects of photochemical smog and how can they be controlled?
Photochemical smog which comprises O3, NO, acrolein (CH2 = CH CHO), formaldehyde (HCHO) and peroxyacetyl nitrate (PAN) causes serious health problems. Both O3 and PAN act as powerful eye irritants. O3 and NO irritate the nose and throat and their high concentration causes headache, chest pain, dryness of throat, cough, difficulty in breathing. Photochemical smog’leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials rubber and painted surfaces.
Control of photochemical smog : Many techniques are used to control or reduce the formation of photochemical smog. If the primary precursors (NO2 & hydrocarbons) of photochemical smog are controlled the secondary precursors such as O3 and PAN will automatically be reduced. Usually catalytical converters are used in the automobiles which prevent the release of NO and unburnt hydrocarbons into the atmosphere. Certain plants, example Pinus, Juniparus, Quercus, Pyrus and vities can metabolise NO and therefore their plantation could help to control the formation of photochemical smog.
What are the reactions involved for ozone layer depletion in the stratosphere?
The upper stratosphere consists of considerable amount of ozone (O3) which protects us from the harmful UV radiations (X = 255 nm) coming from the sun. In recent years, the depletion of the protective O3 shield or layer has been reported. The main reason for the depletion of ozone layer is believed to be the release of chlorofluorocarbons compounds (CFCs) also known as freons, which are extensively used in refrigerators, air-conditioners and are non – reactive, non-flammable, non-toxic organic molecules.
When released in the atmosphere, they mix with the normal atmospheric gases and eventually reach the stratosphere. In stratosphere, they get broken down by powerful UV radiations, releasing chlorine free radical.
The chlorine, free radical (CP.) then reacts with stratospheric ozone to form chlorine monoxide radicals (ClO.) and molecular O2.
Cl + O3(g) → ClO. (g) + O2(g)
Reaction of ClO. with atomic oxygen more Cl. radicals:
CIO. + 0(g) → Cl. (g) + O2(g)
The chlorine radicals are continuously regenerated and cause the breakdown of ozone. Thus CFCs are transporting agents for continuously generating chlorine radicals into the stratosphere and damaging ozone layer-thus causing its depletion
What do you mean by ozone hole? What are its consequences?
In 1980s, atmospheric scientists working in Antarctica reported the depletion of ozone layer commonly known as ozone hole over the south pole. This depletion of ozone shield or ozone hole has hazardous consequences. It will allow more UV radiations to pass through this hole without being prevented into the stratosphere. UV radiations lead to leading of skin, cataract, sunburn, skin cancer, death of many microphytoplanktons, damage to fish productivity etc. Plant proteins get affected easily by UV radiations leading to harmful mutation of cells.
It also increases the evaporation of surface water through the stomata of the leaves and decreases the moisture content of the soil. Increased UV radiations damages paints and fibres causing them to fade faster.
What are the major causes of water pollution? Explain.
Pollution of water originates from human activities. The different causes of water pollution are :
(i) Pathogens : The most serious water pollutants are the disease causing agents called pathogens – Pathogens include bacteria and other organisms that enter water from domestic sewage and animal – excreta. Human excreta contains bacteria such as Escherichia coli and streptococcus faccalis which cause gastrointestinal diseases.
(ii) Organic waste : The other major water pollutant is organic – matter such as leaves, grass, trash etc. The large population of bacteria decomposes organic matter in water. The amount of oxygen which water can hold is consumed by bacteria. The concentration of dissolved oxygen in water is very important for aquatic life.
The lack of oxygen in water causes oxygen dependent aquatic life to die. Thus anaerobic bacteria (which do not require oxygen) begin to break down the organic, waste, producing chemicals that have a foul smell and are harmful to i human life. Aerobic (oxygen requiring) bacteria degrade these organic wastes and keep the water depleted in dissolved oxygen.
(iii) Chemical pollutants : Water being an excellent solvent dissolves inorganic chemicals that include heavy metals like cadmium, mercury, nickel etc, which constitutes an important class of pollutants. These chemicals are extremely dangerous to humans because our body cannot excrete them. Organic chemicals present in petroleum products pollute many sources of water, e.g:, major oil spills in ocean.
Various industrial effluents like polychlorinated biphenyls (PCBs) which are used as cleansing solvents detergents and fertilizers add to the list of water pollutants. There is algae growth due to the presence of phosphates present in fertilizers. These algae growth often release toxins in water.
Have you ever observed any water pollution in your area? What measures would you suggest to control it?
Industrial effluents from paper, textile, chemical industries which are generally allowed to mix with water bodies like rivers should not be allowed to get mixed in such water bodies. Non-biodegradable detergents also should be avoided and only biodegradable detergents and soaps should be used for cleansing or clothes and for baths.
The pH of water should be checked. The pure water has a pH of 7. If its pH is less than 7, it contains acidic impurities like dissolved SO2, H2S. If its pH is above 7, it contains basic impurities like detergents etc. It should be immediately reported to the Pollution Control Board set up by Government of your area and ensure action is taken on the report to control pollution of water bodies-rivers, ponds, streams or lakes.
Use compost instead of chemical fertilizers in gardens. Avoid the use of DDT malathion at home and try to use dried neem leaves to keep insects away. Add a crystal of potassium permanganate (KMnO4) or bleaching powder or alum to the water tank of your house.
What do you mean by Biochemical oxygen demand (BOD)?
Biochemical Oxygen Demand (BOD) : The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of water sample is called Biochemical Oxygen Demand (BOD). The amount of BOD in the water is a measure of the amount of the organic material in water, in terms of how much oxygen will be required to break it down biologically. Clean water would have BOD’value of 17 ppm or more.
Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?
Insecticides, pesticides which are generally used for the protection of the crop cause soil pollution. Even herbicides cause soil pollution. Hence there is need for their judicious use. Earlier (and even now) DDT was put to use to control the damages caused by insects, rodents, weeds and various crop diseases. Pesticides are basically synthetic toxic chemicals with ecological repercussions.
Later other organic toxins like Aldrin and Dieldrin were introduced. Most of such toxins are water-insoluble and non-biodegradable. It causes serious metabolic and physiological disorders in animals. Nowadays herbicides such as sodium chlorate (NaClO3) and sodium arsenite (Na3AsO3) etc. are used. Even they are not environmental friendly.
Control and management of such pollution creating substances is of utmost importance. Domestic waste should be collected in two separate bins-biodegradable like food and vegetable waste and non – biodegradable like plastics, toys, cans etc. Whereas biodegradable waste is deposited in land-fills, non-biodegradable should be recycled.
Minimum use of synthetic fertilizers, pesticides, insecticides, herbicides should be reported to. Proper management of not only domestic wastes, but also medical, agricultural, industrial and mining waste should be resorted to. Use of polythenes should be avoided and should not be allowed to get mixed with the animal fodder.
What are pesticides and herbicides? Explain giving examples.
Pesticides are basically synthetic toxic chemicals with ecological repercussions. Earlier DDT [2, 2 (bis-p-chlorophenyl)-1, 1, 1-trichloroethane] was used to control insect borne disease in crops. Later, as insect resistance of DDT increased, other organic toxins such as Aldrin and Dieldrin were used as pesticides. Most of the organic toxins are water-insoluble and non – biodegradable. Recently more biodegradable products called organo-phosphates and carbamates have been introduced in the market. But these are severe nerve toxins and hence more harmful to humans. There were some pesticide-related deaths of agricultural field workers.
Herbicides: Herbicides are sodium chlorate (NaClO3) and sodium arsinite (Na3AsO3). Most herbicides are toxic to mammals but are not as persistent as organo chlorides. These chemicals decompose in a few months. Like organo – chlorides, these two become concentrated in the food-web. Some herbicides cause birth defects. Studies show that corn-fields sprayed with herbicides are more prone to insects attack than fields that are weeded manually.
What do you mean by green chemistry? How will it help decrease environmental pollution?
Green chemistry is a way of thinking and is about utilizing the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact of pollution on environment. Green chemistry is a production process that would bring about minimum pollution or deterioration to the environment.
The byproducts generated during a process, if not used gainfully, adds to the environmental pollution. Such processes are not only environment unfriendly but also cost ineffective. The waste generation and its disposal both are economically unsound. Utilization of existing knowledge base for reducing the chemical hazards along with the development activities is the foundation of green chemistry.
What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere? Discuss.
The main gases responsible for green house effect are carbon dioxide, methane, water vapours, nitrous oxide, CFCs and ozone. If the amount of CO2 crosses the delicate limit of 0.03%, the natural greenhouse gets disturbed. If the synthetically prepared gases like CFCs (use in refrigerators and air-conditioners) are not released in the atmosphere, burning of leaves, coal etc minimised, emission of oxides of nitrogen from exhaust; pipes of automobiles minimised, the global warming or the greenhouse effect can be minimised.
A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.
Excessive phytoplankton growth within the water of the lake is a cause of water pollution. No doubt, it is bio-degradable. The large population of bacteria decomposes such organic matter in water. The amount of oxygen that water can hold is limited. In cold water, dissolved oxygen (DO) can reach concentration upto 10 ppm. That is why even a moderate amount of organic matter when decomposed in water can deplete water of its dissolved oxygen. The small concentration of dissolved oxygen which was sufficient to support aquatic life gone, the fish die.
How can domestic waste be used as manure?
Domestic waste is collected in small bins A and B. Bin A, coloured green, contains food-left over, vegetable leaves and skin of fruits seeds etc all biodegradable material. Bin B contains non-biodegradable substances like plastics, broken toys, cans, plastic bottles, polythenes etc. Bin B stuff is sent for recycling, whereas Bin A containing biodegradable material is sent through local agencies for land filling to be converted to manure.
For your agriculture field or garden, you have developed a compost producing pit. Discuss the process in the light of bad odour, flies and recycling of wastes for wastes for a good produce.
Domestic waste is of two types-biodegradable and non- biodegradable. Non-biodegradable waste such as plastic, glass, metal scrap etc. are sent for recycling. Biodegradable, waste though giving out foul smell & with lot of flies is a nuisance if left uncovered. It is cause of water pollution and a sewage problem. Mechanically it is broken into pieces and put in the pit and covered with a little of sand in one corner. Due to bacterial action and heat produced, it is converted in due course of time into compost which is an organic manure fit for use in agricultural field or garden.