Methods of Atmospheric Pollution Removal

lyricalwillingMechanics

Feb 22, 2014 (3 years and 3 months ago)

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IB Option E


Environmental Chemistry

Methods of Atmospheric Pollution Removal

Thermal exhaust reactor



exhaust from the car engine is combined with more air and reacts due to the heat of the
exhaust gases. Carbon monoxide is converted into _______________________ and unburned hydrocarbons are also
combusted.


Lean burn engines



by adjusting the carbure
tor the ratio of air:fuel can be altered. The higher the ratio the less carbon
monoxide emitted as more ____________________________________ occurs. Unfortunately, this produces higher
temperatures so more NOx is produced. At lower ratios ______________
__________ but
___________________________ will be emitted.


Catalytic converter



the hot exhaust gases are passed over a catalyst of platinum, rhodium or palladium. These fully
oxidize _________ and unburned ____________, and also catalyze the rxn betwe
en CO and NO.



Alkaline scrubbing & limestone
-
based fluidized beds

Some sulfur is present in _________________ as metal sulfides (i.e. FeS) and can be physically removed by crushing coal
and mixing with water. The more dense sulfides sink to the bottom a
nd the cleaned coal can be skimmed off. Sulfur is
also removed from oil before it is refined by converting it into _____________________.


______________________________ can be removed
from the exhaust of coal burning plants by “
scrubbing

with an alkaline slurry of limestone (_________) and
lime (________). The resulting sludge is used for landfill
or as gypsum

(___________________) t
o make
plasterboard (drywall).


A more modern method known as
fluidized bed
combustion

involves burning the coal on a bed of
limestone which removes the sulfur as
__________________ or _______________ as the coal
burns.


Electrost
atic precipitation

Particulates are solid or liquid particles suspended in
the air. Larger particles can be allowed to settle under
the influence of ____________________ in
sedimentation chambers. For smaller particles, an
electrostatic precipitation
chamber can be used. The
charged particulates are attracted to the oppositely
charged electrodes, which are shaken periodically so
that aggregated particulates fall to the bottom of the
precipitator where they can be removed.


Diagram

(scrubbing)
:













Diagram

(electrostatic precipitation)
:










IB Option E


Environmental Chemistry

3


Acid Deposition

Acid deposition refers to the process by which acidic particles, gases and precipitation leave the atmosphere. Both wet
de
position
(_________________________
_____
__) and dry deposition (______________________
___________) occur.


Rain is naturally _________________ because of dissolved __________, but acid rain has a pH of < ______.

True “acid deposition”

is caused by oxides of nitro
gen and oxides of sulfur
.


Oxides of Sulfur (SO
x
)

(Memorize rxns.)

Sulfur dioxide occurs naturally from volcanoes and is produced industrially from the combustion of sulfur
-
containing
fossil fuels and the smelting of sulfide ores.



In the presence of
sunlight, sulfur dioxide is oxidized to sulfur trioxide.



The oxides can react with water in the air to form sulfurous acid and sulfuric acid:






Oxides of Nitrogen (NO
x
)

(Memorize rxns.)

Nitrogen oxides occur naturally from electrical storms and bacter
ial action. Nitrogen monoxide is produced in the
internal combustion engine and in jet engines.




Oxidation to nitrogen dioxide occurs in the air.



The nitrogen dioxide then reacts with water to form nitric acid and nitrous acid:



…or is oxidized
directly by to nitric acid by oxygen in the presence of water:




Environmental effects of acid deposition

Vegetation



increased acidity in the soil leaches important nutrients, such as Ca
2+
, Mg
2+

and K
+
. Reduction of Mg
2+

can
cause reduction in chloroph
yll and consequently lowers the ability of plants to photosynthesize. Many trees have been
seriously affected by acid rain. Symptoms include stunted growth, thinning of tree tops, and yellowing and loss of
leaves. The main cause is the aluminum leached
from rocks into the groundwater. The Al
3+

ion damages the roots and
prevents the tree from taking up enough water and nutrients to survive.

IB Option E


Environmental Chemistry

4


Lakes and rivers



increased levels of aluminum ions in water can kill fish. Aquatic life is also highly sensiti
ve to pH.
Below pH 6 the number of sensitive fish, such as salmon and minnow, decline as do insect larvae and algae. Snails
cannot survive a pH less than 5.2 and below pH 5.0 many microscopic animal species disappear. Below pH 4.0 lakes are
effectively
dead. The nitrates present in acid rain can also lead to
eutrophication
.


Buildings



stone, such as marble, that contains calcium carbonate is eroded by acid rain. With the sulfuric acid the
calcium carbonate reacts to form calcium sulfate, which can be

washed away by rainwater thus exposing more stone to
corrosion. Salts can also from within the stone that can cause the stone to crack and disintegrate.



Human health



the acids formed when NOx and SOx dissolve in water irritate the mucus membranes and

increase the
risk of respiratory illness, such as asthma, bronchitis and emphysema. In acidic water there is more probability of
poisonous ions, such as Cu2+ and Pb2+, leaching from pipes and high levels of aluminum in water may be linked to
Alzheimer’s
disease (the jury is still out on this one).


Methods to lower or counteract the effects of acid deposition

1.

Lower the amounts of NOx and SOx

formed (i.e. by improved engine design, use of catalytic converters, and
removing sulfur before, during and after c
ombustion of sulfur
-
containing fuels.)

2.

Switch to alternative methods of energy

(i.e. wind and solar power) and reducing the amount of fuel burned (i.e.
by reducing private transport and increasing public transport and designing more efficient power station
s)

3.

Liming of lakes



adding calcium oxide or calcium hydroxide (lime) neutralizes acidity, increases the amount of
calcium ions and precipitates aluminum from solution. This has been shown to be effective in many, but not all,
lakes where it has been trie
d.


Mechanism of acid deposition caused by NO
x

and SO
x

(memorize these rxns.)

In the atmosphere, NO
x

and SO
x
are converted into acids by a free radical mechanism involving hydroxyl free radicals,
OH

. These hydroxyl free radicals are formed either by the
reaction of water vapor with ozone



…or by the reaction of water vapor with oxygen free radicals that are formed when ozone decomposes.



The hydroxyl radicals then react directly with NO
x

and SO
x
in the presence of water to give the dissolved acids.



The role of ammonia in acid deposition

The atmosphere contains trace amounts of ammonia. Ammonia can also be found in the soil due to the action of certain
bacteria known as rhizobia. These can be found in the root nodules of leguminous plants such as pe
as, beans, soy and
clover. The ammonia in the atmosphere can to some extent neutralize the acids to form ammonium sulfate,
______________, and ammonium nitrate, _______________. These ammonium salts, which are the product of a weak
base and a strong acid
, are slightly acidic. As they sink to the ground or are washed out by precipitation the ammonium
ion is deposited and enters the soil where acidification and nitrification can occur.

IB Option E


Environmental Chemistry

5


SMOG

Two types:

1.

Oxidizing smog
:


___________________________________________________



result of NOX rxns in the
presence of UV light (occurs in dry sunshine). This is responsible for the brown cloud of LA.

2.

Reducing smog
:

“pea soup smog”


result of carbon particulates and sulfur dioxid
e (occurs in cold, damp
weather). Creates yellow
-
green smog
---

due to env. controls, largely a thing of the past (thank goodness!!!)


Thermal Inversions
:

occur

when the normal temperature gradient is
______________________

(temp.


with altitude).




Oc
cur in
bowl
-
shaped cities

when it is warm and dry
and there is
_______________________________
.



Mountains, buildings and other barriers around cities
can also promote the development of thermal
inversions by
preventing horizontal movement of air.




Under

these conditions,
________________________
___________________

caps/traps pollutants.




P
hotochemical Smog
(today’s air pollution problem)

-

c
aused by traffic exhaust fumes

Free radical rxns between
__________________________
,
__________________

and
__________________.



Examples of reactions leading to secondary pollutants:



Ozone, O
3

(GOOD up high, BAD nearby)



N
2

+ O
2



2NO



2NO + O
2



2NO
2

(brown)



NO
2

+ sunlight (UV)


NO + O




O
2

+ O




O
3



Peroxyacylnitrates, (PANs)

o

Production of hydrocarbon
radicals:



RH +
O




R


+

OH




alkyl radicals and hydroxyl radicals produced

when VOCs are oxidized



RCH
3

+

OH



RCH
2


+ H
2
O


hydroxyl radicals react with alkanes to produce further alkyl radicals



RCH
2


+ O
2



RCH
2
O
2




these alkyl radicals react with
oxygen

molecules

to produce
peroxy radicals

o

Production of aldehydes



RCH
2
O
2


+ NO




RCH
2
O


+ NO
2



peroxy radicals react with nitrogen monoxide to produce nitrogen dioxide



RCH
2
O


+ O
2



R
CHO

+ HO
2




RCH
2
O


radicals react with oxygen to form aldehydes

o

Production of PANs by hydroxyl radicals and aldehydes



R
CH
O

+

OH



RC
O


+ H
2
O


H
-
atom is removed from an aldehyde



RCO


+ O
2



RCOOO




resulting radical reacts with oxygen molecule to produce a peroxide



Termination step: free radicals in step above + NO


PAN

(relatively stable)

IB Option E


Environmental Chemistry

6


Part 2: Smog, Greenhouse Effect & Ozone Depletion

Greenhouse Effect
:
g
reenhouse gases allow the passage of incoming solar short
-
wavelength radiation
,

but absorb
the longer
-
wavelength radiation from the Earth. Some of the absorbed r
adiation is
re
-
radiated back to Earth.

Table 2: Major greenhouse gases you should know

Gas

Main Source

Heat Trapping Effectiveness
Compared With CO
2

Overall contribution to
increased global warming


Evaporation of oceans

0.1

-


Combustion of fossil fuels and biomass

1



Anaerobic decay of organic matter caused by
intensive farming

30

18%


Artificial fertilizers and combustion of biomass

150

6%


Secondary
pollutant in photochemical smog


12%


Refrigerants, propellants,
foaming agents,
solvents

10,000
-
25,000

14%


Effects of increasing amounts of greenhouse gases on the atmosphere:

o

Rising
____________________________

(from t
hermal expansion of oceans
and m
elting of the polar ice
-
caps
)

o

Changes in precipitation and temperature of regions (causing
_______________________

and droughts)

o

Changes in yield and distribution of commercial
__________________________

o

Changes in distribution of
_______________________

and disease
-
carrying organisms


Stratospheric Ozone Depletion

Table
3:

Formation and depletion of stratospheric ozone
by natural processes

Formation

Depletion









Table 4:

Mechanisms for ozone depletion by anthropogenic sources

C
atalyst

Source

S
ample
M
echanism

(know these)

N
et
E
ffect

CFCs

(most common =
CCl
2
F
2
, a.k.a. Freon
or CFC
-
12)

Refrigerants, propellants for
aerosols, foaming agents for
expanding plastics and
cleaning solvents



O
3

+ O



2
O
2


NO
X

High temperatures inside
combustion engines, power
stations and jet
aeroplanes.






O
3

+ O



2
O
2


IB Option E


Environmental Chemistry

7


Alternatives to CFCs for the future

should have the following characteristics
:



Similar properties to CFC’s, but

o

Low reactivity

o

Low toxicity

o

Low flammability

o

No weak C
-
Cl

bonds that can easily be broken by UV to form radicals

o

Inability to absorb infrared radiation (not greenhouse gases)


Table 5:

Most immediate replacements

Class of chemicals

Lewis structure of example

Benefits

Drawbacks

HCFCs








c
hlorodifluormethane

Decompose more readily than
CFCs and do not build up in
stratosphere

Still contains one C
-
Cl bond
per molecule

HFCs








1,1,1,2
-
tetrafluoro
ethane

Good refrigerant

Flammable

Greenhouse gases

hydrocarbons








2
-
methylpropane

Good refrigerant

Flammable

Greenhouse gases


G
reate
st

ozone depletion
occurs
in polar regions:



Very
_____________

temperatures in
_____________________________



Small amounts of water vapor in air freezes to form
___________________________________________
.



Crystals also c
ontain small amounts of molecules, such as
___________

and ClONO
2
.



Catalytic rxns occur on the surface of the ice crystals to produce species such as hypochlorous acid (HClO) and
chlorine (Cl
2
).



Each spring, the Sun causes these molecules to break down, gi
ving off
________

radicals.



These Cl


radicals catalyze the destruction of
________________________
.



Largest ozone layer holes occur during early spring.



As Sun continues to warm the air, ice crystals disperse and ozone concentrations gradually increase
again.

IB Option E


Environmental Chemistry

8


Part
3
:
Water


Dissolved oxygen

(DO)

in water



One of the most important indicators of
_____________________



Required by most aquatic plants and animals for
______________________________________________



Consumed by microorganisms when they decompose

organic material



The presence of DO in natural water is a
_________________________
sign.



The absence of DO can be a sign of severe pollution.



Fish such as trout require high levels of DO, while fish like carp and catfish can survive with lower levels.



Thu
s the type of organisms found in lakes and streams can be used as an indicator of the overall health of the
water system.




At 20

C, max solubility is 9 ppm (9 mg/L).



DO saturation levels vary with temperature (since oxygen is a gas), but here is a genera
l guideline for stream
water:

o

____________



-

unhealthy, worm
-
infested stream

o

____________




supports some varied organisms

o

____________




-

healthy, trout
-
filled stream

Biological Oxygen Demand (BOD)



Measure of the dissolved oxygen (in ppm) re
quired
to decompose

the organic matter in water biologically.



Water with a
______________________________

without a means of replenishing oxygen (i.e. lakes or slow
moving streams) will not sustain aquatic life.



Fast flowing, churning that aerates water can help
______________________________

as water is oxygenated.



Pure water BOD
_____________



BOD
____________

= polluted


Measurement of BOD
(Winkler method)

1.

Sample of water is
_________________________
with oxygen.

2.

Measured volume of the sample is incubated at fixed temp. for
____________________

(while microorganisms
in the water oxidize the organic material)

3.

After 5 days, determine how much oxygen is left in the system

using
a __________________________________

o

Add

an excess of a manganese (II) salt to the sample.

o

Under alkaline conditions, Mn(II) ions are oxidized to Mn(IV) oxide by the remaining oxygen

o

2Mn
2+
(aq) + 4OH
-
(aq) + O
2
(aq)


2MnO
2
(s) + 2H
2
O(l)

o

KI is then added which is oxidized by the Mn(IV) oxide in acid
ic sol’n to form iodine.

o

MnO
2
(s) + 2I
-
(aq) + 4H
+
(aq)


Mn
2+
(aq) + I
2
(aq) + 2H
2
O(l)

o

The iodine released is then titrated with standard sodium thiosulfate sol’n

o

I
2
(aq) + 2S
2
O
3
2
-
(aq)


S
4
O
6
2
-
(aq) + 2I
-
(aq)

o

By knowing the #moles of iodine produced, the amt. of
oxygen that was present in the sample can be
calculated (thus you know how much oxygen was consumed over the 5 day period)

IB Option E


Environmental Chemistry

9



________________________________________
: too much of a good thing
-

killing a

lake with excess nutrients

o

Excess nitrates (from artificial fertilizers) and phosphates (from artificial fertilizers and detergents) accumulate in
lakes.

o

These nutrients cause CRAZY growth of algae.

o

Excessive algal growth kills all life in the lake.

o

Too
much decaying algae, insufficient DO, products of anaerobic decay poison life in the lake

(plus it blocks the
light from penetrating beneath the surface of the water)
, leading to more decay, etc.


Table
6
:
Products of
Aerobic & Anerobic Decomposition

Element

Aerobic decay product

Anaerobic decay product

C

CO
2



N

NO
3
-



H

H
2
O



S

SO
4
2
-



P

PO
4
3
-




Thermal Pollution

Water that is removed from rivers by power stations can be returned with a temperature increase of up to 20

C.

Concentration of D.O.
_____________________________

with rising temperature.

Oxygen in water may be insufficient for fish to survive.

Metabolic rate of organisms increases with temp., placing additional demand fo
r _____________________

in the water.

Spaw
ning, fertilization and hatching of eggs, is very sensitive to temperature.

Thermal pollution can be reduced by trickling water through a porous material and blowing air in the opposite direction..
The heat is transferred to the
____________

where it is le
ss damaging.


Primary pollutants in waste water and
thei
r sources

o

Nitrates

o

Enter the water from intensive animal farming, excessive use of artificial fertilizers and acid rain.

o

All nitrates are soluble, so it’s very diff
icult to remove them from water.

o

Unpolluted water is generally
_____________

o

Max limit of nitrates in drinking water is
_______________

(or
__________
) as determined by the World
Health Organization.

o

High nitrate levels in drinking water can poison babies under
__________________________
________
.
It makes it difficult for them to get enough oxygen and they my turn blue and suffocate
(infantile
methaemoglobinaemia, a.k.a. blue

baby syndrome)



IB Option E


Environmental Chemistry

1
0


o

Heavy metals

o

Ions in polluted water may include cadmium, mercury, lead, chromium, nickel, copper

and zinc.

Table 7: Sources and hazards of some heavy metals

Metal

Sources

Health hazard

Environmental hazard


Paints, batteries,
agriculture

Causes severe damage to the
nerves and the brain.

Biomagnification

up food chain;
causes reproductive system failure
in fish; inhibits growth and kills fish


Lead pipes, lead paint
and
glazes, leaded fuel
(tetraethyl lead,
banned in US)

Can cause brain damage,
especially in young children

Biomagnification up food chain;

toxic to plants and domestic
animals


Metal plating,

r
echargeable batteries,

p
igments, byproduct of
zinc refining

Makes enzymes ineffective by
replacing zinc; causes brittle
bones; can lead to lung and
kidney cancer

Toxic to fish; produces birth
defects

in mice

o

Pesticides

o

Include insecticides, fungicides and herbicides, which kill insects, fungi and weeds respectively.

o

Since they are poisonous, they can be problematic when washed off land into water.

o

Example:
_______

(derived from old imprecise name
d
ichloro
d
iphenyl
t
richloroethane)

pesticide
introduced into environment at low levels harmless to birds and
animals (including humans), but because it is stable and fat soluble it
accumulated and became concentrated over time via
____________________
_______
____________________
. Has been banned in many countries because
it had disastrous effects on bird life.



o

Dioxin
s

o

Group of compounds whose structure con
sists of two benzene rings connected via one or two oxygen
atoms. Each benzene ring can have up to four chlorine atoms.

o

2,3,7,8
-
t
etrachlorodibenzodioxin

(a.k.a. “dioxin”)

is
_______

times more poisonous than the cyanide ion.


o

Sources: one of the herbic
ides present in Agent Orange used during the Vietnam war, and also forms
when waste materials containing organochloro
-
compounds are not incinerated at high enough
temperatures.

Accumulate in
___________
and liver cells and therefore persist in environment
.

o

Sympto
ms of exposure include cirrhosis of the liver, damage to the heart and memory

and depression.
Also c
ause
s

malfunctions in fetuses.


o

Polychlorinated biphenyls, PCBs

o

Can have up to
_______

chlorines.

o

Source: used in electrical transformers and capacitors because of
their chemical stability and high electrical
__________________
.

o

Persist in environment and accumulate in fatty tissue.

o

Reproduce reproductive efficient, impair learning in children and
are thought to be carcinogenic.

IB Option E


Environmental Chemistry

11


Waste Water Treatment

-

Purpose: remove
_________________________

materials, reduce
____________

and kill
______________________________

before the water is returned to the environment.


Primary treatment:

1.

______________________________
:

w
aste water passed through screens and grids to filter out debris.

2.

______________________________
: w
ater is then passed into a sedimentation tank where it is allowed to
settle.

Resulting

sludge

is removed from the bottom of

the tank.



Secondary

treatment:

________________________________________
:

organic material is oxidized and broken down.
Involves introduction of bacteria and aeration. Large blowers are used to bubble air, or air enriched with oxygen,
through waste w
ater mixed with bacteria
-
laden sludge. Thus bacteria help to aerobically decompose the contents. The
water, containing decomposed suspended particles, is passed through another sedimentation tank and the sludge is
removed for further processing. After s
econdary treatment, about 90% of the organic oxygen
-
demanding wastes and
suspended particles have been removed.


Terti
ary treatment:

involves
specialized chemical, biological or physical processes which further treat the water and
remov
e

remaining organic
material,
heavy metals, phosphates and nitrates by chemical or biological processes.




Precipitation
: Heavy metals such as Cd, Pb and Hg can be removed as sulfide salts, which have low solubility.



Ion exchange
: all nitrates are soluble and are thus more dif
ficult to remove. Resins or zeolites can be used to exchange the nitrate ions in
polluted water with hydroxide ions. Positive ions can also be exchanged with H+ ions. The resulting OH
-

and H+ will then combine for
form water.



Biological methods
: algal p
onds can also be used to remove nitrate ions

by using the nitrate ions as nutrients which are then converted
back into atmospheric nitrogen.



Activated carbon bed method
: activated carbon consists of tiny carbon granules with large surface area which have
been treated and
activated by high temperatures. Activated carbon readily adsorbs organic chemicals from the water.


Obtaining fresh water from sea water

Multistage
________________________________
:
sea water is heated in a series of coiled popes and then

introduced
into a
partially

evacuated chamber. Under reduced pressure, the water boils instantly. The water vapor produced
condenses when it makes c
ontact with cold
-
w
ater pip
es carrying sea water. In this way, heat released when water
condenses is used

to preheat more sea water.

__________________________________________
:
high
pressure (up to 70 atm) is applied to seawater and pure water
is pushed through a semipermeable membrane made of cellulose ethanoate, leaving the salts behind.

IB Option E


Environmental Chemistry

12


Part
4
:
Soil & W
aste

S
oil

Soil Degradation
:

soil quality has been altered in such a way that it lowers crop production. Can be caused by changing
weather patterns, or by anthropogenic factors such as acidification, contamination, erosion and salinization (from
industrialization, irrigation, overgr
azing, overharvesting of trees).



Salinization
:
from constant or excess irrigation. Salts from irrigated water accumulate in soil long after the
water evaporates. Plants die from toxic levels of salt or inability to take up water from salty soil with
their roots.



Nutrient depletion
:
intensive farming


no time for fields to be fallow; no organic fertilizers used



Soil pollution
:

can be caused by industrial discharge, use of pesticides and fertilizers, illegal dumping of spent
engine oil, etc.; all leads

to groundwater pollution.


Soil Organic Matter (SOM)



organic constituents of the soil



Biological



humus provides source of energy and source of essential nutrient elements nitrogen, phosphor
us
and sulfur to sustain healthy growth.



Physical


humus help
s soil retain moisture; dark color of humus absorbs heat.



Chemical



humus
acts like clay with its cation exchange capacity. Contains active sites which enable it to bind to
nutrient cations. Also acts as acid
-
base buffer.


Common
organic
soil pollutants



Hydrocarbons and other VOCs



P
esticides, herbicides & fungicides



Polyaromatic hydrocarbons (PAHs)



Polychlorinated biphenyls (PCBs)

Waste

Table
7
:
Methods of Waste Disposal

Method

Advantages

Disadvantages

Landfill

Efficient method to deal with large volumes

Filled land can be used for building or other
community purposes

Local residents may object to new sites

Once filled, needs time to settle, and
may
require maintenance as methane released

Open Dumping

Inexpensive

Convenient (for the dumper)

Causes air and ground water pollution

Health hazard: encourages rodents and insects

Unsightly

Ocean Dumping

Source of nutrients

Convenient and inexpensive

Danger to marine animals

Pollutes the sea

Incineration

Reduces volume

Requires minimal space

Produces stable, odor
-
free residue

Can be used as a source of energy

Expensive to build and operate

Can cause pollutants, e.g. dioxins, if inefficiently
burned

Requires energy

Recycling

Provides a sustainable environment

Expensive

Difficulty in separating different materials; not
possible in all cases

IB Option E


Environmental Chemistry

13


Table
8
: Recycling

Material

Description

Comments

Metals

Mainly aluminum and steel. The metal are sorted, then
melted and either reused directly or added to the
purification stage of metals formed from their ores

Particularly important for metals such as
aluminum, which require large amounts
of energy to produce directly from ore

Paper

Taken to the plant, sorted i
n grades. Washed to remove
inks, etc., made into a slurry to form new types of paper,
such as newspaper and toilet rolls.

Energy required to transport. Composting
may be as efficient.

Glass

Sorted by color, washed, crushed, then melted and
molded into
new products

Glass is not degraded during the recycling
process, so can be recycled many times

Plastics

Industrial plastic is already sorted, but household waste
plastic must first be sorted. Degraded to monomers by
pyrolysis, hydrogenation, gasification,

and thermal
cracking, then repolymerized

Fewer pollutants formed, and energy
used to recycle rather than to make from
crude oil. Better to reuse than to recycle.


Table
9
: Plastics Recycling Codes

(no need to memorize, just an “FYI” item)

Code
Symbol

Abb
rev.

Name

Typical Use

1

PET

Polyethylene terephthalate

Fizzy drink bottles and oven
-
ready meal trays

2

HDPE

High
-
density polyethylene

Bottles for milk and washing
-
up liquids

3

PVC

Polyvinyl chloride

Food trays, cling film, bottles for squash, mineral
water and shampoo

4

LDPE

Low
-
density polyethylene

Carrier bags and bin liners

5

PP

Polypropylene

Margarine tubs, microwavable meal trays

6

PS

Polystyrene

Yogurt pots, foam meat or fish trays, hamburger
boxes, vending cups, plastic cutlery, protective
packaging for electronic goods and toys

7

OTHER

Any other plastics that don’t fall
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IB Option E


Environmental Chemistry

14



Water and Soil

Precipitation of
h
eavy
m
etal
i
ons and
p
hosphates from
w
ater

When a salt is
labeled “insoluble,” it really means that it has a very low/slight solubility in water.



Solubility product, k
sp

=


Many metal sulfides have very low solubility products, but can still be precipitated out by bubbling other compounds
through the water, ma
king use of the common ion effect.


Example:

l
ead

removal






Example:

phosphate removal
































IB Option E


Environmental Chemistry

15



Cation exchange capacity (CEC)

o

Both soil organic matter (SOM) and the clay particles in soil have a negative charge and will attract and bond to
positively charged cations.

o

Basic cations: Ca
2+
, Mg
2+
, Na
+

o

Acidic cations: H
+
, Al
3+

o

Cation

exchange capacity (CEC) = the amount of positively charged cations that a soil can hold.

o

These cations are exchanged with cations such as hydrogen ions on the root hairs of plants and thus provide
nutrients to the plant.

o

Soil pH

o

Low pH = high concentratio
n of acidic cations

o

High pH = more basic ions

o

Below 5 is bad for most plants (acid ions such as Al3+ are harmful to plants)

o

Acid rain increases amount of aluminum cations by lowering pH of soil (above pH 5 aluminum ions are
virtually all precipitated out o
f the soil solution).

o

Soil has a buffering capacity, but it is still sometimes necessary to add lime to soil to raise the pH and
increase the concentration of basic ions held by the clay and SOM.

o

In addition to capturing nutrient cations

needed by plants, the SOM can also bind to organic and inorganic
compounds in the spoil
which

helps to reduce the
negative

environmental effects of
contaminants

such as
pesticides
, heavy
metal

ions and other pollutants.