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 carburetor 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 between 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 and 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 (___________________) to make
plasterboard (drywall).
Diagram (scrubbing):
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.
Electrostatic 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 (electrostatic precipitation):
IB Option E
Environmental Chemistry
Acid Deposition
Acid deposition refers to the process by which acidic particles, gases and precipitation leave the atmosphere. Both wet
deposition (________________________________) 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 nitrogen and oxides of sulfur.
Oxides of Sulfur (SOx) (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 (NOx) (Memorize rxns.)
Nitrogen oxides occur naturally from electrical storms and bacterial 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 Ca2+, Mg2+ and K+. Reduction of Mg2+ can
cause reduction in chlorophyll 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 Al3+ ion damages the roots and
prevents the tree from taking up enough water and nutrients to survive.
3
IB Option E
Environmental Chemistry
Lakes and rivers – increased levels of aluminum ions in water can kill fish. Aquatic life is also highly sensitive 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 combustion 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 stations)
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 tried.
Mechanism of acid deposition caused by NOx and SOx (memorize these rxns.)
In the atmosphere, NOx and SOx 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 NOx and SOx 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 peas, 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.
4
IB Option E
Environmental Chemistry
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 dioxide (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).



Occur 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.
Photochemical Smog (today’s air pollution problem) - caused by traffic exhaust fumes
Free radical rxns between __________________________,__________________ and __________________.
Examples of reactions leading to secondary pollutants:
 Ozone, O3 (GOOD up high, BAD nearby)
☼ N2 + O2  2NO
☼ 2NO + O2  2NO2 (brown)
☼ NO2 + sunlight (UV)  NO + O
☼ O2 + O  O3
 Peroxyacylnitrates, (PANs)
o Production of hydrocarbon radicals:

RH + O  R + OH
alkyl radicals and hydroxyl radicals produced when VOCs are oxidized

RCH3 + OH  RCH2 + H2O
hydroxyl radicals react with alkanes to produce further alkyl radicals

RCH2 + O2  RCH2O2
these alkyl radicals react with oxygen molecules to produce peroxy radicals
o Production of aldehydes

RCH2O2 + NO  RCH2O + NO2
peroxy radicals react with nitrogen monoxide to produce nitrogen dioxide
 RCH2O + O2  RCHO + HO2
RCH2O radicals react with oxygen to form aldehydes
o Production of PANs by hydroxyl radicals and aldehydes
 RCHO + OH  RCO + H2O
H-atom is removed from an aldehyde

RCO + O2  RCOOO
resulting radical reacts with oxygen molecule to produce a peroxide

Termination step: free radicals in step above + NO  PAN (relatively stable)
5
IB Option E
Environmental Chemistry
Part 2: Smog, Greenhouse Effect & Ozone Depletion
Greenhouse Effect: greenhouse gases allow the passage of incoming solar short-wavelength radiation, but absorb
the longer-wavelength radiation from the Earth. Some of the absorbed radiation is re-radiated back to Earth.
Table 2: Major greenhouse gases you should know
Gas
Main Source
Heat Trapping Effectiveness
Compared With CO2
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 thermal expansion of oceans and melting 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
Catalyst
CFCs
(most common =
CCl2F2, a.k.a. Freon
or CFC-12)
Source
Refrigerants, propellants for
aerosols, foaming agents for
expanding plastics and
cleaning solvents
NOX
High temperatures inside
combustion engines, power
stations and jet aeroplanes.
Sample Mechanism (know these)
Net Effect
O3 + O → 2O2
O3 + O → 2O2
6
IB Option E
Environmental Chemistry
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
HCFCs
Benefits
Drawbacks
Decompose more readily than
CFCs and do not build up in
stratosphere
Still contains one C-Cl bond
per molecule
Good refrigerant
Flammable
Greenhouse gases
Good refrigerant
Flammable
Greenhouse gases
chlorodifluormethane
HFCs
1,1,1,2-tetrafluoroethane
hydrocarbons
2-methylpropane
Greatest ozone depletion occurs in polar regions:
 Very _____________ temperatures in _____________________________
 Small amounts of water vapor in air freezes to form ___________________________________________.
 Crystals also contain small amounts of molecules, such as ___________ and ClONO2.
 Catalytic rxns occur on the surface of the ice crystals to produce species such as hypochlorous acid (HClO) and
chlorine (Cl2).
 Each spring, the Sun causes these molecules to break down, giving 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.
7
IB Option E
Environmental Chemistry
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.
Thus 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 general 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) required 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 2Mn2+(aq) + 4OH-(aq) + O2(aq) → 2MnO2(s) + 2H2O(l)
o KI is then added which is oxidized by the Mn(IV) oxide in acidic sol’n to form iodine.
o MnO2(s) + 2I-(aq) + 4H+(aq) → Mn2+(aq) + I2(aq) + 2H2O(l)
o The iodine released is then titrated with standard sodium thiosulfate sol’n
o I2(aq) + 2S2O32-(aq) → S4O62-(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)
8
IB Option E
Environmental Chemistry
________________________________________: 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
CO2
N
NO3-
H
H2O
S
SO42-
P
PO43-
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 for _____________________ in the water.
Spawning, 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 less damaging.
Primary pollutants in waste water and their 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 difficult 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)
9
IB Option E
o
Environmental Chemistry
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
Paints, batteries,
agriculture
Health hazard
Causes severe damage to the
nerves and the brain.
Lead pipes, lead paint
and glazes, leaded fuel
(tetraethyl lead,
banned in US)
Metal plating,
rechargeable batteries,
pigments, byproduct of
zinc refining
Can cause brain damage,
especially in young children
Makes enzymes ineffective by
replacing zinc; causes brittle
bones; can lead to lung and
kidney cancer
Environmental hazard
Biomagnification up food chain;
causes reproductive system failure
in fish; inhibits growth and kills fish
Biomagnification up food chain;
toxic to plants and domestic
animals
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 dichlorodiphenyltrichloroethane)
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
Dioxins
o Group of compounds whose structure consists 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-tetrachlorodibenzodioxin (a.k.a. “dioxin”) is _______ times more poisonous than the cyanide ion.
o
o
o
Sources: one of the herbicides 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.
Symptoms of exposure include cirrhosis of the liver, damage to the heart and memory and depression.
Also causes malfunctions in fetuses.
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.
10
IB Option E
Environmental Chemistry
Waste Water Treatment - Purpose: remove _________________________ materials, reduce ____________ and kill
______________________________ before the water is returned to the environment.
Primary treatment:
1. ______________________________: waste water passed through screens and grids to filter out debris.
2. ______________________________: water 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 water 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 secondary treatment, about 90% of the organic oxygen-demanding wastes and
suspended particles have been removed.
Tertiary treatment: involves specialized chemical, biological or physical processes which further treat the water and
remove 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 difficult 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 ponds 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 contact with cold-water pipes 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.
11
IB Option E
Environmental Chemistry
Part 4: Soil & Waste
Soil
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, overgrazing, 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, phosphorus
and sulfur to sustain healthy growth.
 Physical – humus helps 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
 Pesticides, herbicides & fungicides


Polyaromatic hydrocarbons (PAHs)
Polychlorinated biphenyls (PCBs)
Waste
Table 7: Methods of Waste Disposal
Method
Advantages
Landfill
Efficient method to deal with large volumes
Filled land can be used for building or other
community purposes
Open Dumping
Inexpensive
Convenient (for the dumper)
Disadvantages
Local residents may object to new sites
Once filled, needs time to settle, and may
require maintenance as methane released
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
Provides a sustainable environment
Expensive to build and operate
Can cause pollutants, e.g. dioxins, if inefficiently
burned
Requires energy
Expensive
Difficulty in separating different materials; not
possible in all cases
Recycling
12
IB Option E
Environmental Chemistry
Table 8: Recycling
Material Description
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
Paper
Taken to the plant, sorted in grades. Washed to remove
inks, etc., made into a slurry to form new types of paper,
such as newspaper and toilet rolls.
Glass
Sorted by color, washed, crushed, then melted and
molded into new products
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
Comments
Particularly important for metals such as
aluminum, which require large amounts
of energy to produce directly from ore
Energy required to transport. Composting
may be as efficient.
Glass is not degraded during the recycling
process, so can be recycled many times
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
Abbrev. Name
Typical Use
Symbol
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 E.g. melamine, which is often used in plastic plates
into any of the above categories and cups
Table 10: Nuclear Waste
Type
Low Level Waste
Characteristics low activity; radioisotopes have relatively short half lives
Examples
Disposal
items that have been used in areas where radioactive
materials are handled (rubber gloves, paper towels,
protective clothing, etc.)
Stored in steel containers in concrete-lined vaults OR stored in
cooling ponds until it loses much of its activity and then;
filtered through ion exchange to remove Sr and Cs and then
dispersed
High Level Waste
high activity; radioisotopes have long
half-lives
spent fuel rods from nuclear power
plants
Fuel rods cased in ceramic or glass,
packed in metal containers and buried
deep in the earth in a location where
geologists believe it won’t affect
groundwater
13
IB Option E
Environmental Chemistry
Water and Soil
Precipitation of heavy metal ions and phosphates from water
When a salt is labeled “insoluble,” it really means that it has a very low/slight solubility in water.
Solubility product, ksp =
Many metal sulfides have very low solubility products, but can still be precipitated out by bubbling other compounds
through the water, making use of the common ion effect.
Example: lead removal
Example: phosphate removal
14
IB Option E
Environmental Chemistry
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: Ca2+, Mg2+, Na+
o Acidic cations: H+, Al3+
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 concentration 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 of 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.
15