environmental chemistry

Question 1

what is the troposphere

Answer 1

lowest region of atmosphere in which human beings and organisms live

Question 2

range of troposphere

Answer 2

extends up to the height of ~10 km from sea level

Question 3

stratosphere range

Answer 3

10 km to 50 km above sea level

Question 4

turbulent dusty zone containing air and water vapour

Answer 4

stratosphere

Question 5

SO₂ respiratory diseases

Answer 5

asthma, bronchitis, emphysema, irritation to eyes

Question 6

SO₂ effect on plants

Answer 6

leads to stiffness of flower buds which eventually fall off from plants

Question 8

when is rate of production of NO₂ faster

Answer 8

when nitric oxide reacts w ozone present in the atmosphere

NO_(g) + O₃ –> NO₂ + O₂

Question 9

high conc of NO₂ effect on plants

Answer 9

retards rate of photosynthesis and damages leaves of plants

Question 10

what causes irritant red haze in traffic and congested places

Answer 10

oxides of nitrogen

Question 11

how are hydrocarbons formed in the environment

Answer 11

by incomplete combustion of fuel used in automobiles

Question 11

Acute respiratory disease in children due to what

Answer 11

NO₂

Question 12

hydrocarbons effect on humans and plants

Answer 12

1. hydrocarbons are carcinogenic i.e. they cause cancer
2. they harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs

Question 13

name greenhouse gases

Answer 13

carbon dioxide, methane, water vapour, nitrous oxide, CFCs, ozone

Question 14

how is methane produced naturally

Answer 14

• 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

Question 15

normal pH of rainwater

Answer 15

normally rainwater has a pH of 5.6 due to the presence of H⁺ ions formed by the rxn of rainwater and carbon dioxide

Question 16

major contributors to acid rain

Answer 16

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

Question 17

classical smog:
environment
components
alternate name

Answer 17

• 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

Question 18

photochemical smog:
environment
components
alternate name

Answer 18

• 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

Question 19

what happens when pollutants- hydrocarbons and nitric oxide build up to sufficiently high levels?

Answer 19

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

Question 20

what happens to the nascent oxygen formed

Answer 20

combine with O₂ to form O₃

ozone formed reacts rapidly w NO to form NO₂

Question 20

what components of photochemical smog are oxidising agents

Answer 20

NO₂ and O₃

Question 21

what does unburnt hydrocarbon form on reaction with ozone

Answer 21

chemicals like formaldehyde, acrolein(CH₂=CHCH=O), peroxyacteyl nitrate (PAN)

Question 22

common components of photochemical smog

Answer 22

ozone, nitric acid, acrolein, formaldehyde, peroxyacetyl nitrate

Question 23

health problems caused by photochemical smog

Answer 23

1. ozone and PAN: eye irritants
2. ozone and nitric oxide irritae nose and throat and high conc causes headache, chest pain, dry throat, cough, difficulty breathing

Question 24

main reason of ozone layer depletion

Answer 24

release of CFCs, also known as freons

they are nonreactive, non flammable, non toxic organic molecules and used in refrigerators, ACs

Question 25

what happens to CFCs in the stratosphere

Answer 25

get broken down by powerful UV radiations, release chlorine free radicals
CF₂Cl₂ –UV–> Cl^. + C^.F₂Cl

Question 26

what rxn with chlorine radical and ozone

Answer 26

forms chlorine monoxide radicals

Question 27

rxn of chlorine monoxide radical with atomic oxygen forms?

Answer 27

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

Question 28

BOD

Answer 28

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

Question 29

BOD value of
1. clean water
2. highly polluted water

Answer 29

1. less than 5 ppm
2. 17 ppm or more

Question 30

fluoride deficiency in water

Answer 30

its deficiency in drinking water is harmful to man and causes diseases like tooth decay

Question 31

what do F^- ions do to enamel

Answer 31

make it much harder by converting hydroxyapatite [3(Ca₃(PO₄)₂.Ca(OH)₂] into much harder fluorapatite [3(Ca₃(PO₄)₂.CaF₂]

Question 32

what does high conc of F^- ion cause

Answer 32

above 2 ppm conc causes brown mottling of teeth
over 10 ppm affects bones and teeth

Question 33

prescribed upper limit concentration of lead in drinking water

Answer 33

about 50 ppb
can damage liver, reproductive system

Question 34

excessive sulphate

Answer 34

above 500ppm causes laxative effect

Question 35

excess nitrate

Answer 35

max limit is 50 ppm in drinking water

can cause disease like methemoglobinemia (blue baby syndrome)

Question 36

max conc Cd

Answer 36

0.005 ppm

Question 37

max conc Zn

Answer 37

5 ppm

Question 38

max conc Cu

Answer 38

3 ppm

Question 39

max conc Al

Answer 39

0.2 ppm

Question 40

max conc Mn

Answer 40

0.05 ppm

Question 41

max conc Fe

Answer 41

0.2 ppm