ALLIED CHEMISTRY PAPER – I
UNIT - II
1. Write a note on Silicones
Silicone used for a mobile phone protector.
Silicones are largely inert, man-made compounds with a wide variety of forms and uses.
Typically heat-resistant, nonstick, and rubberlike, they are commonly used in cookware,
medical applications, sealants, adhesives, lubricants, and insulation.
Silicones are polymers that include silicon together with carbon, hydrogen, oxygen, and
sometimes other chemical elements.
Properties
Some of the most useful properties of silicone include:
1. Thermal stability (constancy of properties over a wide operating range of −100 to
250 °C).
2. Though not a hydrophobe, the ability to repel water and form watertight seals.
3. Excellent resistance to oxygen, ozone and UV light (sunlight). This has led to
widespread use in the construction industry (e.g. coatings, fire protection, glazing
seals), and automotive industry (external gaskets, external trim).
4. Good electrical insulation. Because silicone can be formulated to be electrically
insulative or conductive, it is suitable for a wide range of electrical applications.
5. Non-stick.
6. Low chemical reactivity.
7. Low toxicity, but does not support microbiological growth.
8. High gas permeability: at room temperature (25 °C) the permeability of silicone
rubber for gases like oxygen is approximately 400 times that of butyl rubber,
making silicone useful for medical applications (though precluding it from
applications where gas-tight seals are necessary).
Technical details
More precisely called polymerized siloxanes or polysiloxanes, silicones are mixed
inorganic-organic polymers with the chemical formula [R2SiO]n, where R is an organic
group such as methyl, ethyl, or phenyl. These materials consist of an inorganic siliconoxygen backbone (…-Si-O-Si-O-Si-O-…) with organic side groups attached to the
silicon atoms, which are four-coordinate.
In some cases organic side groups can be used to link two or more of these -Si-Obackbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking,
silicones can be synthesized with a wide variety of properties and compositions. They can
vary in consistency from liquid to gel to rubber to hard plastic. The most common
siloxane is linear polydimethylsiloxane (PDMS), a silicone oil. The second largest group
of silicone materials is based on silicone resins, which are formed by branched and cagelike oligosiloxanes.
Synthesis
Silicones are synthesized from chlorosilanes, tetraethoxysilane, and related compounds.
In the case of PDMS, the starting material is dimethyldichlorosilane, which reacts with
water as follows:
n Si(CH3)2Cl2 + n H2O → [Si(CH3)2O]n + 2n HCl
During polymerization, this reaction evolves potentially hazardous hydrogen chloride
gas. For medical uses, a process was developed where the chlorine atoms in the silane
precursor were replaced with acetate groups, so that the reaction product of the final
curing process is nontoxic acetic acid (vinegar). As a side effect, the curing process is
also much slower in this case. This is the chemistry used in many consumer applications,
such as silicone caulk and adhesives.
Silane precursors with more acid-forming groups and fewer methyl groups, such as
methyltrichlorosilane, can be used to introduce branches or cross-links in the polymer
chain. Ideally, each molecule of such a compound becomes a branch point. This can be
used to produce hard silicone resins. Similarly, precursors with three methyl groups can
be used to limit molecular weight, since each such molecule has only one reactive site
and so forms the end of a siloxane chain.
Modern silicone resins are made with tetraethoxysilane, which reacts in a more mild and
controllable manner than chlorosilanes.
Uses
Aquarium joints
Glass aquarium manufacturers have used 100% silicone sealant exclusively from its
inception in order to join glass plates, making aquariums of every size and shape. Glass
joints made with silicone sealant can withstand hundreds of metric tons of pressure,
making obsolete the original aquarium construction method using angle-iron and putty.
This same silicone is also used to make hinges in aquarium lids or even for minor repairs.
It is worth noting that not all commercial silicones are safe for aquarium manufacture,
nor is silicone used for the manufacture of acrylic aquariums as silicones do not adhere
long term to plastics.
Automotive
In the automotive field, silicone grease is typically used as a lubricant for brake
components since it is stable at high temperatures, is not water-soluble and is far less
likely than other lubricants to foul.
Coatings
Silicone films can be applied to silica-based substrates like glass to form a covalently
bonded hydrophobic coating.
Cookware

As a low taint, non-toxic material, silicone can be used where contact with food is
required. Silicone is becoming an important product in the cookware industry,
particularly bakeware and kitchen utensils.

It is used as an insulator in heat resistant potholders and similar, however it is
more conductive of heat than the less dense fiber-based ones. Silicone oven mitts
are able to withstand temperatures up to 675 °F (357 °C), and allow reaching into
boiling water.

Molds for chocolate, ice, cookies, muffins, etc.

Some novel designs are steamer, egg boiler, vegetables cooker, cooking lids, pot
handle, kitchen mats, etc.
Defoaming
Silicones are used as active compound in defoamers due the the low water solubility and
good spreading properties.
Dry cleaning
Liquid silicone can be used as a dry cleaning solvent. Touted as an "environmentally
friendly" alternative to the traditional perchloroethylene (or perc) solvent, the
decamethylpentacyclosiloxane (D5) process has been patented by the company
GreenEarth Cleaning.
The solvent degrades into silica and trace amounts of water and CO2, and waste
produced from the D5 drycleaning process is nontoxic and nonhazardous. This
significantly reduces the environmental impact of a typically high-polluting industry.
Additionally, liquid silicone is chemically inert, meaning it does not react with fabrics or
dyes during the cleaning process. This reduces the amount of fading and shrinking that
most dry-cleaned garments experience.
Electronics
Electronic components are sometimes encased in silicone to increase stability against
mechanical and electrical shock, radiation and vibration. This is often called "potting".
Silicones are used where durability and high performance are demanded of components
under hard conditions, such as in space (satellite technology). They are selected over
polyurethane or epoxy encapsulation when a wide operating temperature range is
required (−65 to 315 °C). Silicones also have the advantage of little exothermic heat rise
during cure, low toxicity, good electrical properties and high purity.
The use of silicones in electronics is not without problems, however. Silicones are
relatively expensive and can be attacked by solvents. Silicone easily migrates as either a
liquid or vapor onto other components.
Silicone contamination of electrical switch contacts can lead to failures by causing an
increase in contact resistance, often late in the life of the contact, well after any testing is
completed. Use of silicone-based spray products in electronic devices during
maintenance or repairs can cause later failures.
Firestops
Silicone foams have been used in North American buildings in an attempt to firestop
openings within fire-resistance-rated wall and floor assemblies to prevent the spread of
flames and smoke from one room to another.
Silicone foam firestops have been the subject of controversy and press attention due to
smoke development from pyrolysis of combustible components within the foam,
hydrogen gas escape, shrinkage and cracking. These problems have been exposed by
whistleblower Gerald W. Brown and have led to a large number of reportable events
among licensees (operators of nuclear power plants) of the Nuclear Regulatory
Commission (NRC).
When properly installed, silicone-foam firestops can be fabricated for building code
compliance. Advantages include flexibility and high dielectric strength. Disadvantages
include combustibility (hard to extinguish) and significant smoke development.
Silicone can also be found in air craft technology.
Lubricants
Silicone greases are used for many purposes, such as bicycle chains. A dry-set lubricant
is delivered with a solvent carrier to penetrate the chain. The solvent evaporates, leaving
a clear film that lubricates but does not attract dirt and grit as much as a traditional "wet"
lubricant.
Silicone personal lubricants are also available, for use in medical procedures or sexual
activity.
Medicine
Silicone, particularly the gel form, is used in bandages and dressings, in breast implants
and a variety of other medical uses.
Polydimethylsiloxane (PDMS) has been used as the hydrophobic block of amphiphilic
synthetic block copolymers used to form the vesicle membrane of polymersomes.
Moldmaking
Two-part silicone systems are used to create rubber molds which can be used for
production casting of resins, foams, rubber and low-temp alloys.
A mold made of silicone generally requires little or no mold release or surface
preparation as most materials do not adhere to moldmaking silicone.
Synthesis of Silicones
The most common method for preparing silicones involves reacting a chlorosilane with
water. This produces a hydroxyl intermediate, which condenses to form a polymer-type
structure. The basic reaction sequence is represented as:
This is the favoured route although other raw materials such as alkoxysilanes can be
used. Chlorosilanes and other silicone precursors are synthesised using the “Direct
Process”, involving the reaction of elemental silicone with an alkyl halide thus,
Si + RX → RnSiX4-n (where n = 0-4)
Preparation of silicone elastomers requires the formation of high molecular weight
(generally greater than 500000g/mol). To produce these types of materials requires difunctional precursors, which form linear polymer structures. Mono and tri-functional
precursors form terminal structures and branched structures respectively.
2. Write a note on Natural gas
Natural gas is a gas consisting primarily of methane. It is found associated with fossil
fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in
marshes, bogs, and landfills. It is an important fuel source, a major feedstock for
fertilizers, and a potent greenhouse gas.
Natural gas is often informally referred to as simply gas, especially when compared to
other energy sources such as electricity. Before natural gas can be used as a fuel, it must
undergo extensive processing to remove almost all materials other than methane. The byproducts of that processing include ethane, propane, butanes, pentanes and higher
molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen.
Sources
3. Write a note on Water gas.
The water-gas shift reaction (WGS/Dussan Reaction) is a chemical reaction in which
carbon monoxide reacts with water to form carbon dioxide and hydrogen:
CO + H2O → CO2 + H2
The water-gas shift reaction is an important industrial reaction. It is often used in
conjunction with steam reforming of methane or other hydrocarbons, which is important
for the production of high purity hydrogen for use in ammonia synthesis. The carbon
monoxide can also be generated by bogs or other waste regenerative means by
physical/chemical processes such as bog and landfill fires.
4. Write a note on Producer gas
Producer Gas is a generic term referring to:

Wood gas : produced in a gasifier to power cars with ordinary internal
combustion engines.

Town gas : manufactured gas, originally produced from coal, for sale to
consumers and municipalities.

Syngas : used as a fuel source or as an intermediate for the production of other
chemicals.
In old movies and stories, when describing suicide by "turning on the gas" and leaving an
oven door open without lighting the flame, they were talking about producer gas. It was
odorless and poisonous. Modern 'natural gas' used in homes is far less toxic, and has an
onion-like scent added to it for identifying leaks.
In the UK, Producer Gas, also called suction gas, specifically means a fuel gas made
from coke, anthracite or other carbonaceous material. Air is passed over the red-hot
carbonaceous fuel and carbon monoxide is produced. The reaction is exothermic and
proceeds as follows:
2C + O2 → 2CO
The nitrogen in the air remains unchanged and dilutes the gas, giving it a very low
calorific value. After "scrubbing", to remove tar, the gas may be used to power gas
turbines (which are well-suited to fuels of low calorific value), spark ignited engines
(where 100% petrol fuel replacement is possible) or diesel internal combustion engines
5. Write about Biogas
Pipes carrying biogas (foreground), natural gas and condensate
Main articles: Natural gas and biofuel
Biogas typically refers to a gas produced by the biological breakdown of organic matter
in the absence of oxygen. Biogas originates from biogenic material and is a type of
biofuel.
One type of biogas is produced by anaerobic digestion or fermentation of biodegradable
materials such as biomass, manure or sewage, municipal waste, green waste and energy
crops[1]. This type of biogas comprises primarily methane and carbon dioxide. The other
principal type of biogas is wood gas which is created by gasification of wood or other
biomass. This type of biogas is comprised primarily of nitrogen, hydrogen, and carbon
monoxide, with trace amounts of methane.
The gases methane, hydrogen and carbon monoxide can be combusted or oxidized with
oxygen. Air contains 21% oxygen. This energy release allows biogas to be used as a fuel.
Biogas can be used as a low-cost fuel in any country for any heating purpose, such as
cooking. It can also be used in modern waste management facilities where it can be used
to run any type of heat engine, to generate either mechanical or electrical power. Biogas
can be compressed, much like natural gas, and used to power motor vehicles and in the
UK for example is estimated to have the potential to replace around 17% of vehicle fuel.
Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some parts of
the world.
Production
(LFG) or digester gas. A biogas plant is the name often given to an anaerobic digester
that treats farm wastes or energy crops.
Biogas can be produced utilizing anaerobic digesters. These plants can be fed with energy
crops such as maize silage or biodegradable wastes including sewage sludge and food
waste.
Applications
Biogas can be utilized for electricity production on sewage works, in a CHP gas engine,
where the waste heat from the engine is conveniently used to heat the digester; cooking,
space heating, water heating and process heating. If compressed, it can replace
compressed natural gas for use in vehicles, where it can fuel an internal combustion
engine or fuel cells and is a much more effective displacer of carbon dioxide than the
normal use in on site CHP plants.
Methane within biogas can be concentrated via a biogas upgrader to the same standards
as fossil natural gas; when it is, it is called biomethane. If the local gas network permits
it the producer of the biogas may be able to utilize the local gas distribution networks.
Gas must be very clean to reach pipeline quality, and must be of the correct composition
for the local distribution network to accept. Carbon dioxide, Water, hydrogen sulfide and
particulates must be removed if present.
6. Define Fertilizer.
Fertilizers are chemical compounds applied to promote plant and fruit growth. Fertilizers
are usually applied either through the soil (for uptake by plant roots) or, by foliar feeding
(for uptake through leaves).
Fertilizers can be placed into the categories of organic fertilizers (composed of plant or
animal matter), or inorganic fertilizers (made of simple, non-carbonaceous chemicals or
minerals).
'Organic' fertilizers are composed of 'naturally' occurring compounds such as peat
manufactured through natural processes (such as composting) or naturally occurring
mineral deposits; or in the case of 'inorganic' fertilizers, manufactured through chemical
processes (such as the Haber process) or from naturally occurring deposits that have been
chemically altered (e.g. concentrated triple superphosphate[1]).
7. W hat are the differences between organic vs. Non-organic fertilizers.
Both organic and inorganic fertilizers were called "manure" derived from the French
expression for manual (of or belonging to the hand) tillage, however, this term is
currently restricted to organic manure. Though nitrogen is plentiful in the Earth's
atmosphere, relatively few plants engage in nitrogen fixation (conversion of atmospheric
nitrogen to a plant-accessible form).
It is believed by some that 'organic' agricultural methods are more environmentally
friendly and better maintain soil organic matter (SOM) levels. There are some scientific
studies that support this position.
8. Write a note on Ammonium sulfate
Ammonium sulfate (IUPAC-recommended spelling; also ammonium sulphate in British
English), (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most
common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and
24% sulfur as sulfate anions. In fertilizer the purpose of the sulfate is to reduce the soil
pH.
Uses
It is used largely as an artificial fertilizer for alkaline soils. In the soil the sulfate ion is
released and forms bisulfate, lowering the pH balance of the soil (as do other sulfate
compounds such as aluminium sulfate), while contributing essential nitrogen for plant
growth.
It is also used as an agricultural spray adjuvant for water soluble insecticides, herbicides,
and fungicides. There it functions to bind iron and calcium cations that are present in both
well water and plant cells. It is particularly effective as an adjuvant for 2,4-D (amine),
glyphosate, and glufosinate herbicides.
It is also used in the preparation of other ammonium salts.
In biochemistry, ammonium sulfate precipitation is a common method for purifying
proteins by precipitation. As such, ammonium sulfate is also listed as an ingredient for
many United States vaccines per the Center for Disease Control.
Ammonium sulfate is also a food additive.
A saturated solution of ammonium sulfate in heavy water (D2O) is used as an external
standard in sulfur (33S) NMR spectroscopy with shift value of 0 ppm.
It has also been used in flame retardant compositions acting much like Diammonium
phosphate. As a flame retardant, it lowers the combustion temperature of the material,
decreases maximum weight loss rates, and causes an increase in the production of residue
or char.
Preparation
Ammonium sulfate is made by reacting synthetic ammonia (or by-product ammonia from
coke-ovens) with sulfuric acid
2 NH3 + H2SO4 → (NH4)2SO4
A mixture of ammonia gas and water vapor is introduced into a reactor that contains a
saturated solution of ammonium sulfate and about 2 to 4% of free sulfuric acid at 60 °C.
Concentrated sulfuric acid is added to keep the solution acidic, and to retain its level of
free acid. The heat of reaction keeps reactor temperature at 60 °C.
Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a
reaction chamber filled with ammonia gas. The heat of reaction evaporates all water
present in the system, forming a powdery salt.
Ammonium sulfate also is manufactured from gypsum salt (CaSO4·2H2O). Finely
divided gypsum salt is added to an ammonium carbonate solution. Calcium carbonate
precipitates out, leaving ammonium sulfate in the solution.
(NH4)2CO3 + CaSO4 → (NH4)2SO4 + CaCO3
Ammonium sulfate occurs naturally as the rare mineral mascagnite in volcanic fumaroles
and due to coal fires on some dumps.
9. Write a note on Urea
Urea is an organic compound with the chemical formula (NH2)2CO.
Urea is also known by the International Nonproprietary Name (rINN) carbamide, as
established by the World Health Organization. For example, the medicinal compound
hydroxyurea (old British Approved Name) is now hydroxycarbamide. Other names
include carbonyl diamide, and carbonyldiamine.
Urea was first discovered in urine in 1773 by the French chemist Hilaire Rouelle.
It was the first organic compound to be artificially synthesized from inorganic starting
materials, in 1828 by Friedrich Wöhler, who prepared it from silver isocyanate through a
reaction with ammonium chloride:[1]
AgNCO + NH4Cl → (NH2)2CO + AgCl
Although Wöhler was attempting to prepare ammonium cyanate, by forming urea, the
results of his work implicitly discredited vitalism: the theory that the chemicals of living
organisms are fundamentally different from inanimate matter. This started the discipline
of organic chemistry.
10. Write a note on Superphosphate
Superphosphate is a fertilizer produced by the action of concentrated sulfuric acid on
powdered phosphate rock.
Ca3(PO4)2 + 2H2SO4 → Ca(H2PO4)2 + 2CaSO4
11. Write a note on Triple superphosphate
Triple Superphosphate is a fertilizer produced by the action of concentrated phosphoric
acid on ground phosphate rock.
3Ca3(PO4)2·CaF2 + 4H3PO4 + 9H2O --> 9Ca(H2PO4)2 + CaF2
The active ingredient of the product, monocalcium phosphate, is identical to that of
superphosphate, but without the presence of calcium sulfate that is formed if sulfuric acid
is used instead of phosphoric acid. The phosphorus content of triple superphosphate (17 23% P; 44 to 52% P2O5) is therefore greater than that of superphosphate (7 - 9.5% P; 16
to 22% P2O5). Triple superphosphate was the most common phosphate (P) fertilizer in the
USA until the 1960s, when ammonium phosphates became more popular. It is produced
in granular and nongranular form and is used both in fertilizer blends (with potassium and
nitrogen fertilizers) and by itself.
Potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula KNO3. A
naturally occurring mineral source of nitrogen, KNO3 constitutes a critical oxidizing
component of black powder/gunpowder. In the past it was also used for several
kinds of burning fuses, including slow matches. Because potassium nitrate readily
precipitates.
12. Write a note on Ammonium nitrate
The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical
formula NH4NO3, is a white crystalline solid at room temperature and standard pressure.
It is commonly used in agriculture as a high-nitrogen fertilizer, and it has also been used
as an oxidizing agent in explosives, including improvised explosive devices.
Ammonium nitrate is used in cold packs, as hydrating the salt is an endothermic process.
13. Explain about Air Pollution
Air pollution from World War II production.
Pollution is the introduction of contaminants into an environment that causes instability,
disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms .
Pollution can take the form of chemical substances, or energy, such as noise, heat, or
light energy. Pollutants, the elements of pollution, can be foreign substances or energies,
or naturally occurring; when naturally occurring, they are considered contaminants when
they exceed natural levels. Pollution is often classed as point source or nonpoint source
pollution. The Blacksmith Institute issues annually a list of the world's worst polluted
places. In the 2007 issues the ten top nominees are located in Azerbaijan, China, India,
Peru, Russia, Ukraine and Zambia.
Modern awareness
Early Soviet poster, before the modern awareness: "The smoke of chimneys is the breath
of Soviet Russia"
Nuclear weapons continued to be tested in the Cold War, sometimes near inhabited areas,
especially in the earlier stages of their development. The toll on the worst-affected
populations and the growth since then in understanding about the critical threat to human
health posed by radioactivity has also been a prohibitive complication associated with
nuclear power. Though extreme care is practiced in that industry, the potential for
disaster suggested by incidents such as those at Three Mile Island and Chernobyl pose a
lingering specter of public mistrust. One legacy of nuclear testing before most forms were
banned has been significantly raised levels of background radiation.
International catastrophes such as the wreck of the Amoco Cadiz oil tanker off the coast
of Brittany in 1978 and the Bhopal disaster in 1984 have demonstrated the universality of
such events and the scale on which efforts to address them needed to engage. The
borderless nature of atmosphere and oceans inevitably resulted in the implication of
pollution on a planetary level with the issue of global warming. Most recently the term
persistent organic pollutant (POP) has come to describe a group of chemicals such as
PBDEs and PFCs among others. Though their effects remain somewhat less well
understood owing to a lack of experimental data, they have been detected in various
ecological habitats far removed from industrial activity such as the Arctic, demonstrating
diffusion and bioaccumulation after only a relatively brief period of widespread use.
Growing evidence of local and global pollution and an increasingly informed public over
time have given rise to environmentalism and the environmental movement, which
generally seek to limit human impact on the environment.
14. Explain about Forms of pollution
The major forms of pollution are listed below along with the particular pollutants relevant
to each of them:

Air pollution, the release of chemicals and particulates into the atmosphere.
Common gaseous air pollutants include carbon monoxide, sulfur dioxide,
chlorofluorocarbons (CFCs) and nitrogen oxides produced by industry and motor
vehicles. Photochemical ozone and smog are created as nitrogen oxides and
hydrocarbons react to sunlight. Particulate matter, or fine dust is characterized by
their micrometre size PM10 to PM2.5.

Water pollution, by the release of waste products and contaminants into surface
runoff into river drainage systems, leaching into groundwater, liquid spills,
wastewater discharges, eutrophication and littering.

Soil contamination occurs when chemicals are released by spill or underground
leakage. Among the most significant soil contaminants are hydrocarbons, heavy
metals, MTBE[7], herbicides, pesticides and chlorinated hydrocarbons.

Littering

Radioactive contamination, resulting from 20th century activities in atomic
physics, such as nuclear power generation and nuclear weapons research,
manufacture and deployment. (See alpha emitters and actinides in the
environment.)

Noise pollution, which encompasses roadway noise, aircraft noise, industrial
noise as well as high-intensity sonar.

Light pollution, includes light trespass, over-illumination and astronomical
interference.

Visual pollution, which can refer to the presence of overhead power lines,
motorway billboards, scarred landforms (as from strip mining), open storage of
trash or municipal solid waste.

Thermal pollution, is a temperature change in natural water bodies caused by
human influence, such as use of water as coolant in a power plant.
15. What are the Effects in Human health from pollution?
Adverse air quality can kill many organisms including humans. Ozone pollution can
cause respiratory disease, cardiovascular disease, throat inflammation, chest pain, and
congestion. Water pollution causes approximately 14,000 deaths per day, mostly due to
contamination of drinking water by untreated sewage in developing countries. Oil spills
can cause skin irritations and rashes. Noise pollution induces hearing loss, high blood
pressure, stress, and sleep disturbance. Mercury has been linked to developmental deficits
in children and neurologic symptoms. Lead and other heavy metals have been shown to
cause neurological problems. Chemical and radioactive substances can cause cancer and
as well as birth defects.
Ecosystems

Sulphur dioxide and nitrogen oxides can cause acid rain which lowers the pH
value of soil.

Nitrogen oxides are removed from the air by rain and fertilise land which can
change the species composition of ecosystems.

Soil can become infertile and unsuitable for plants. This will affect other
organisms in the food web.

Smog and haze can reduce the amount of sunlight received by plants to carry out
photosynthesis and leads to the production of tropospheric ozone which damages
plants.

Invasive species can out compete native species and reduce biodiversity. Invasive
plants can contribute debris and biomolecules (allelopathy) that can alter soil and
chemical compositions of an environment, often reducing native species
competitiveness.

Biomagnification describes situations where toxins (such as heavy metals) may
pass through trophic levels, becoming exponentially more concentrated in the
process.

Carbon dioxide emissions cause ocean acidification, the ongoing decrease in the
pH of the Earth's oceans as CO2 becomes dissolved.

The emission of greenhouse gases leads to global warming which affects
ecosystems in many ways.
Regulation and monitoring
To protect the environment from the adverse effects of pollution, many nations
worldwide have enacted legislation to regulate various types of pollution as well as to
mitigate the adverse effects of pollution.
16. What are the methods adopted in Pollution control?
Pollution control is a term used in environmental management. It means the control of
emissions and effluents into air, water or soil. Without pollution control, the waste
products from consumption, heating, agriculture, mining, manufacturing, transportation
and other human activities, whether they accumulate or disperse, will degrade the
environment. In the hierarchy of controls, pollution prevention and waste minimization
are more desirable than pollution control.
Pollution control devices



Dust collection systems
o
Cyclones
o
Electrostatic precipitators
o
Baghouses
Scrubbers
o
Baffle spray scrubber
o
Cyclonic spray scrubber
o
Ejector venturi scrubber
o
Mechanically aided scrubber
o
Spray tower
o
Wet scrubber
Sewage treatment
o
API oil-water separators[18][12]
o
Sedimentation (water treatment)
o
Dissolved air flotation (DAF)
o
Activated sludge biotreaters
o
Biofilters
o

Powdered activated carbon treatment
Vapor recovery systems
Perspectives
The earliest precursor of pollution generated by life forms would have been a natural
function of their existence. The attendant consequences on viability and population levels
fell within the sphere of natural selection. These would have included the demise of a
population locally or ultimately, species extinction. Processes that were untenable would
have resulted in a new balance brought about by changes and adaptations. At the
extremes, for any form of life, consideration of pollution is superseded by that of
survival.
For humankind, the factor of technology is a distinguishing and critical consideration,
both as an enabler and an additional source of byproducts. Short of survival, human
concerns include the range from quality of life to health hazards. Since science holds
experimental demonstration to be definitive, modern treatment of toxicity or
environmental harm involves defining a level at which an effect is observable. Common
examples of fields where practical measurement is crucial include automobile emissions
control, industrial exposure (eg Occupational Safety and Health Administration (OSHA)
PELs), toxicology (eg LD50), and medicine (eg medication and radiation doses).
"The solution to pollution is dilution", is a dictum which summarizes a traditional
approach to pollution management whereby sufficiently diluted pollution is not
harmful.[19][20] It is well-suited to some other modern, locally-scoped applications such as
laboratory safety procedure and hazardous material release emergency management. But
it assumes that the dilutant is in virtually unlimited supply for the application or that
resulting dilutions are acceptable in all cases.
Such simple treatment for environmental pollution on a wider scale might have had
greater merit in earlier centuries when physical survival was often the highest imperative,
human population and densities were lower, technologies were simpler and their
byproducts more benign. But these are often no longer the case. Furthermore, advances
have enabled measurement of concentrations not possible before. The use of statistical
methods in evaluating outcomes has given currency to the principle of probable harm in
cases where assessment is warranted but resorting to deterministic models is impractical
or unfeasible. In addition, consideration of the environment beyond direct impact on
human beings has gained prominence.
Yet in the absence of a superseding principle, this older approach predominates practices
throughout the world. It is the basis by which to gauge concentrations of effluent for legal
release, exceeding which penalties are assessed or restrictions applied. The regressive
cases are those where a controlled level of release is too high or, if enforceable, is
neglected. Migration from pollution dilution to elimination in many cases is confronted
by challenging economical and technological barriers.
17. Write a note on Greenhouse gases and global warming
Historical and projected CO2 emissions by country.
Carbon dioxide, while vital for photosynthesis, is sometimes referred to as pollution,
because raised levels of the gas in the atmosphere are affecting the Earth's climate.
Disruption of the environment can also highlight the connection between areas of
pollution that would normally be classified separately, such as those of water and air.
Recent studies have investigated the potential for long-term rising levels of atmospheric
carbon dioxide to cause slight but critical increases in the acidity of ocean waters, and the
possible effects of this on marine ecosystems.
18. Explain about Soil contamination
Excavation showing soil contamination at a disused gasworks
Soil contamination is caused by the presence of man-made chemicals or other alteration
in the natural soil environment. This type of contamination typically arises from the
rupture of underground storage tanks, application of pesticides, percolation of
contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes
from landfills or direct discharge of industrial wastes to the soil. The most common
chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other
heavy metals. This occurrence of this phenomenon is correlated with the degree of
industrializations and intensities of chemical usage.
19. Write a note on Acid rain
Acid rain is rain or any other form of precipitation that is unusually acidic. It has harmful
effects on plants, aquatic animals, and infrastructure. Acid rain is mostly caused by
human emissions of sulfur and nitrogen compounds which react in the atmosphere to
produce acids. In recent years, many governments have introduced laws to reduce these
emissions.
Forests and other vegetation
Definition
"Acid rain" is a popular term referring to the deposition of wet (rain, snow, sleet, fog and
cloudwater, dew) and dry (acidifying particles and gases) acidic components. A more
accurate term is “acid deposition”. Distilled water, which contains no carbon dioxide, has
a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater
than 7 are bases. “Clean” or unpolluted rain has a slightly acidic pH of about 5.2, because
carbon dioxide and water in the air react together to form carbonic acid, a weak acid (pH
5.6 in distilled water), but unpolluted rain also contains other chemicals.
H2O (l) + CO2 (g) → H2CO3 (aq)
Carbonic acid then can ionize in water forming low concentrations of hydronium and
carbonate ions:
2 H2O (l) + H2CO3 (aq)
CO32− (aq) + 2 H3O+ (aq)
2 H+ (aq) + Mg2+ (clay)
2 H+ (clay) + Mg2+ (aq)
Soil chemistry can be dramatically changed when base cations, such as calcium and
magnesium, are leached by acid rain thereby affecting sensitive species
Human health
Scientists have suggested direct links to human health. Fine particles, a large fraction of
which are formed from the same gases as acid rain (sulfur dioxide and nitrogen dioxide),
have been shown to cause illness and premature deaths such as cancer and other diseases.
For more information on the health effects of aerosols see particulate health effects.
Acid rain can also cause damage to certain building materials and historical monuments.
This results when the sulfuric acid in the rain chemically reacts with the calcium
compounds in the stones (limestone, sandstone, marble and granite) to create gypsum,
which then flakes off.
CaCO3 (s) + H2SO4 (aq)
CaSO4 (aq) + CO2 (g) + H2O (l)
This result is also commonly seen on old gravestones where the acid rain can cause the
inscription to become completely illegible. Acid rain also causes an increased rate of
oxidation for iron. Visibility is also reduced by sulfate and nitrate aerosols and particles
in the atmosphere.
20. Write a note on Ozone depletion
Image of the largest Antarctic ozone hole ever recorded (September 2006).
Ozone depletion describes two distinct, but related observations: a slow, steady decline
of about 4% per decade in the total volume of ozone in Earth's stratosphere (ozone layer)
since the late 1970s, and a much larger, but seasonal, decrease in stratospheric ozone over
Earth's polar regions during the same period. The latter phenomenon is commonly
referred to as the ozone hole. In addition to this well-known stratospheric ozone
depletion, there are also tropospheric ozone depletion events, which occur near the
surface in polar regions during spring.
The detailed mechanism by which the polar ozone holes form is different from that for
the mid-latitude thinning, but the most important process in both trends is catalytic
destruction of ozone by atomic chlorine and bromine. The main source of these halogen
atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds,
commonly called freons, and of bromofluorocarbon compounds known as halons. These
compounds are transported into the stratosphere after being emitted at the surface. Both
ozone depletion mechanisms strengthened as emissions of CFCs and halons increased.
CFCs and other contributory substances are commonly referred to as ozone-depleting
substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths
(270–315 nm) of ultraviolet light (UV light) from passing through the Earth's
atmosphere, observed and projected decreases in ozone have generated worldwide
concern leading to adoption of the Montreal Protocol banning the production of CFCs
and halons as well as related ozone depleting chemicals such as carbon tetrachloride and
trichloroethane. It is suspected that a variety of biological consequences such as increases
in skin cancer, damage to plants, and reduction of plankton populations in the ocean's
photic zone may result from the increased UV exposure due to ozone depletion.
Ozone cycle overview
Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: oxygen
atoms (O or atomic oxygen), oxygen gas (O2 or diatomic oxygen), and ozone gas (O3 or
triatomic oxygen). Ozone is formed in the stratosphere when oxygen molecules
photodissociate after absorbing an ultraviolet photon whose wavelength is shorter than
240 nm. This produces two oxygen atoms. The atomic oxygen then combines with O2 to
create O3. Ozone molecules absorb UV light between 310 and 200 nm, following which
ozone splits into a molecule of O2 and an oxygen atom. The oxygen atom then joins up
with an oxygen molecule to regenerate ozone. This is a continuing process which
terminates when an oxygen atom "recombines" with an ozone molecule to make two O2
molecules: O + O3 → 2 O2
Global monthly average total ozone amount.
The overall amount of ozone in the stratosphere is determined by a balance between
photochemical production and recombination.
Ozone can be destroyed by a number of free radical catalysts, the most important of
which are the hydroxyl radical (OH·), the nitric oxide radical (NO·) and atomic chlorine
(Cl·) and bromine (Br·). All of these have both natural and anthropogenic (manmade)
sources; at the present time, most of the OH· and NO· in the stratosphere is of natural
origin, but human activity has dramatically increased the levels of chlorine and bromine.
These elements are found in certain stable organic compounds, especially
chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being
destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl
and Br atoms are liberated from the parent compounds by the action of ultraviolet light,
e.g. ('h' is Planck's constant, 'ν' is frequency of electromagnetic radiation)
CFCl3 + hν → CFCl2 + Cl
The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic
cycles. In the simplest example of such a cycle, a chlorine atom reacts with an ozone
molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen
molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of
ozone (i.e., O3) to yield another chlorine atom and two molecules of oxygen. The
chemical shorthand for these gas-phase reactions is:
Cl + O3 → ClO + O2
ClO + O3 → Cl + 2 O2
The overall effect is a decrease in the amount of ozone. More complicated mechanisms
have been discovered that lead to ozone destruction in the lower stratosphere as well.
A single chlorine atom would keep on destroying ozone (thus a catalyst) for up to two
years (the time scale for transport back down to the troposphere) were it not for reactions
that remove them from this cycle by forming reservoir species such as hydrogen chloride
(HCl) and chlorine nitrate (ClONO2). On a per atom basis, bromine is even more efficient
than chlorine at destroying ozone, but there is much less bromine in the atmosphere at
present. As a result, both chlorine and bromine contribute significantly to the overall
ozone depletion. Laboratory studies have shown that fluorine and iodine atoms
participate in analogous catalytic cycles. However, in the Earth's stratosphere, fluorine
atoms react rapidly with water and methane to form strongly-bound HF, while organic
molecules which contain iodine react so rapidly in the lower atmosphere that they do not
reach the stratosphere in significant quantities. Furthermore, a single chlorine atom is
able to react with 100,000 ozone molecules.