environmental chemistry Flashcards
what is the troposphere
lowest region of atmosphere in which human beings and organisms live
range of troposphere
extends up to the height of ~10 km from sea level
stratosphere range
10 km to 50 km above sea level
turbulent dusty zone containing air and water vapour
stratosphere
SO2 respiratory diseases
asthma, bronchitis, emphysema, irritation to eyes
SO2 effect on plants
leads to stiffness of flower buds which eventually fall off from plants
when is rate of production of NO2 faster
when nitric oxide reacts w ozone present in the atmosphere
NO(g) + O3 –> NO2 + O2
high conc of NO2 effect on plants
retards rate of photosynthesis and damages leaves of plants
what causes irritant red haze in traffic and congested places
oxides of nitrogen
how are hydrocarbons formed in the environment
by incomplete combustion of fuel used in automobiles
Acute respiratory disease in children due to what
NO2
hydrocarbons effect on humans and plants
- hydrocarbons are carcinogenic i.e. they cause cancer
- they harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs
name greenhouse gases
carbon dioxide, methane, water vapour, nitrous oxide, CFCs, ozone
how is methane produced naturally
- When vegetation is burnt, digested or rotted in the absence of oxygen
- large amt of methane is released in paddy fields, coal mines, rotting garbage dumps and by fossil fuels
normal pH of rainwater
normally rainwater has a pH of 5.6 due to the presence of H+ ions formed by the rxn of rainwater and carbon dioxide
major contributors to acid rain
SO2 and NO2 after oxidation and reaction with water because polluted air usually contains particulate matter that catalyses the oxidation
2SO2 + O2 + 2H2O —> 2H2SO4
4NO2 + O2 + 2H2O —> 4HNO3
classical smog:
environment
components
alternate name
- occurs in cool humid climate
- it is a mixture of smoke, fog, SO2
- chemically it is a reducing mixture and so it is also called reducing smog
photochemical smog:
environment
components
alternate name
- occurs in warm, bright, sunny climate
- main components result from action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories
- has high conc of oxidising agents and is called oxidising smog
what happens when pollutants- hydrocarbons and nitric oxide build up to sufficiently high levels?
A chain reaction occurs from their interaction with sunlight in which NO is converted into NO2.
NO2 absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom
NO2 — hv—> NO + O
what happens to the nascent oxygen formed
combine with O2 to form O3
ozone formed reacts rapidly w NO to form NO2
what components of photochemical smog are oxidising agents
NO2 and O3
what does unburnt hydrocarbon form on reaction with ozone
chemicals like formaldehyde, acrolein(CH2=CHCH=O), peroxyacteyl nitrate (PAN)
common components of photochemical smog
ozone, nitric acid, acrolein, formaldehyde, peroxyacetyl nitrate
health problems caused by photochemical smog
- ozone and PAN: eye irritants
- ozone and nitric oxide irritae nose and throat and high conc causes headache, chest pain, dry throat, cough, difficulty breathing
main reason of ozone layer depletion
release of CFCs, also known as freons
they are nonreactive, non flammable, non toxic organic molecules and used in refrigerators, ACs
what happens to CFCs in the stratosphere
get broken down by powerful UV radiations, release chlorine free radicals
CF2Cl2 –UV–> Cl. + C.F2Cl
what rxn with chlorine radical and ozone
forms chlorine monoxide radicals
rxn of chlorine monoxide radical with atomic oxygen forms?
more chlorine radicals which are continuously regenerated and cause the breakdown of ozone.
thus CFCs are transporting agents for continuously generating chlroine radicals into the stratosphere and damaging the ozone layer
BOD
amt of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called Biochemical Oxygen Demand
BOD value of
1. clean water
2. highly polluted water
- less than 5 ppm
- 17 ppm or more
fluoride deficiency in water
its deficiency in drinking water is harmful to man and causes diseases like tooth decay
what do F- ions do to enamel
make it much harder by converting hydroxyapatite [3(Ca3(PO4)2.Ca(OH)2] into much harder fluorapatite [3(Ca3(PO4)2.CaF2]
what does high conc of F- ion cause
above 2 ppm conc causes brown mottling of teeth
over 10 ppm affects bones and teeth
prescribed upper limit concentration of lead in drinking water
about 50 ppb
can damage liver, reproductive system
excessive sulphate
above 500ppm causes laxative effect
excess nitrate
max limit is 50 ppm in drinking water
can cause disease like methemoglobinemia (blue baby syndrome)
max conc Cd
0.005 ppm
max conc Zn
5 ppm
max conc Cu
3 ppm
max conc Al
0.2 ppm
max conc Mn
0.05 ppm
max conc Fe
0.2 ppm
