kimia lingkungan 1
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ENVIRONMENTAL CHEMISTRY
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ISTILAH TERKAIT
• Environmental Science
•
Ecology• Environmental Chemistry
• Toxicological Chemistry
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What is Environmental Science ?
Env. Sc. will be defined as the study of earth, air,
water, and living environments, and the
effects of technology thereon
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What is Ecology ?
Ecology is the study of environmental factors
that affect organisms and how organisms
interact with these factors and with each
other
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What is Environmental Chemistry ?
• Environmental Chemistry may be defined as
the study of the sources, reactions, transport,
effects, and fates of chemical species in water,
soil, air and living environments and the
effects of technology thereon
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What is Toxicological Chemistry ?
Toxicological Chemistry is the chemistry of toxic
substances with emphasis upon their
interactions with biologic tissue and living
organisms
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WATER, AIR, EARTH, LIFE &TECHNOLOGY
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WATER AND THE HYDROSPHERE
Water covers about 70% of Earth’s surface
In the Oceans as vast reservoir of saltwater
On land as surface water in lakes and rivers
Underground as groundwater In the atmosphere as water vapor
In the polar icecaps as solid ice
In boilers or municipal water distribution systems
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POLLUTANT
A substance present in greater than natural concentration
as a result of human activity that has a net detrimental
effect upon its environment
CONTAMINANT
A substance that cause deviations from the normal
composition of an environment
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FUNDAMENTALS OF AQUATIC CHEMISTRY
AQUATIC CHEMISTRY
The study dealing with water in rivers, lakes,estuaries and oceans, as well as ground water, and
water treatment systems.
It involves phenomena determining thedistribution and circulation of chemical species innatural water
Required some understanding of the sources,
transport, characteristics and composition of water
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THE HYDROLOGIC CYCLE
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IMPORTANT PROPERTIES OF WATER
Colorless, allowing light
required for photosynthesisto reach considerable
depths in bodies of water
Transparent to visible and
longer-wavelength fractionof uv light
High solubility of ionic
substances
Highest dielectric constant
Transport of nutrients and
waste product
Excellent solvent
EFFECT ANDSIGNIFICANCE
PROPERTY
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Ice floats, verticalcirculation restricted in
stratified bodies of water
Maximum density as aliquid at 4oC
Determines transfer of heat
and water molecules
between the atmosphere and
bodies of water
Higher heat of
evaporation than any
other material
Stabilization of temperaturesof organisms and
geographical regions
Higher heat capacitythan other liquid except
ammonia
EFFECT AND
SIGNIFICANCEPROPERTY
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The water molecule
• Made up of 2 hydrogen atoms bonded to an oxygen
atom
• They form an angle of 105o
• The oxygen atom attracts the negative electron more
strongly than do the hydrogen atom, the watermolecule behave like a dipole
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The water molecule
Water dissolves many ionic compounds and salts that
do not dissolve in other liquids
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The water molecule
Hydrogen bonds
• Holds the water molecules together in largegroups
• Help to hold some solute molecules or ions in
solution
• Aids in retaining extremely small particles
called colloidal particles in suspension in water
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THE CHARACTERISTICS OF BODIES OF WATER
SURFACE WATER occurs primarily in
STREAMS
LAKES
RESERVOIR
Stratification of a Lake
AQUATIC LIFE
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AQUATIC LIFE
AQUATIC LIFE
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AQUATIC LIFE
MAJOR AQUATIC CHEMICAL PROCESSES
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MAJOR AQUATIC CHEMICAL PROCESSES
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GASES IN WATER
Crucial to the welfare of living species in water
Fish require oxygen and give off CO2
Algae performing photosynthesis needs CO2 and produceoxygen
The equilibrium between molecules of gas in the atmosphereand in solution
G(g) G(aq)
SOLUBILITIES OF GASES
Henry Law : the solubility of a gas in a liquid is proportionalto the partial pressure of that gas in contact with the liquid
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• [X(aq)] = K x Px
[X(aq)] = Solubility of a gas X in water
K = Henry’s Law constant to a particular gas at
a specified temperature
Px = The partial pressure of the gas
• In calculating the solubility of a gas in water, a correction
must be made for the partial pressure of water bysubstracting it from the total pressure of the gas
At th 25oC th ti l f t i 0 0313 t
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At the 25oC the partial pressure of water is 0.0313 atm.Considering that dry air is 20.95% by volume oxygen, theconcentration of oxygen in water saturated with air at 1.0 atmand 25oC :
PO2 = (1-0.0313) atm x 0.2095
= 0.2029 atm
[O2(aq)] = K x PO2 = 1.28.10-3 x 0.2029
= 2.60 x 10-4
M= 2.60 x 10-4 x 32 g/L
= 8.32 mg/L = 8.32 ppm
If organic matter is represented by the formula {CH2O}, the
comsumption of oxygen in water by degradation of organicmatter maybe expressed by the following biochemical reaction:
{CH2O} + O2 → CO2 + H2O
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The weight of organic material required to consume the
8,3 mg of oxygen in a liter water in equilibrium with the
atmosphere at 25oC is given by a simple
stoichiometric calculation based on the previousequation, which yields a value of 7.8 mg of {CH2O}.
Thus, the microorganism-mediated degradation of only 7or 8 mg of organic material can completely consume the
oxygen in one liter of water initially saturated with air at
25oC
h l b l f d h
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The solubility of gases decrease with increasing T.
Clausius-Clayperon equation:
Log C2/C1 = ∆H/2.303R (1/T1 – 1/T2)
Especially important in the case of oxygen
The solubility of oxygen in water decrease from 14.74mg/L at 0oC to 7.03 mg/L at 35oC.
b d
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Carbon Dioxide in Water
• The most important weak acid in water
• Present in all natural waters and waste-waters becauseof the presence carbon dioxide in air and its productionfrom microbial decay of organic matter
• Rainfall from even an absolutely unpolluted atmosphere
is slightly acidic due to the presence of dissolved CO2
• Carbon dioxide, and its ionization products, bicarbonateion and carbonate ion have an extremely importantinfluence upon the chemistry of water
many minerals are deposited as salts of the carbonateion
algae in water utilize dissolved CO2 in the synthesis of biomass
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•The CO HCO CO 2- system in water may be
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•The CO2-HCO3-CO32 system in water may be
described by the equations,
CO2(aq) + H2O HCO3- + H+
K a1 = 4,45.10-7
HCO3- CO3
2- + H+
K a2 = 4,69.10-11
The predominance species formed by CO2 dissolvedin water depends upon pH
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These fraction designated as are given by the
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These fraction designated as x are given by thefollowing expression:
2COα=
-23-
32
2
COHCOCO
CO
-
3HCO
α =
-2
3
-
32
-
3
COHCOCO
HCO
-2
3CO
α =
-2
3
-
32
-2
3
COHCOCO
CO
Substitution of the expression for K and K into the
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Substitution of the expression for Ka1 and Ka2 into the expression gives the the fraction of species as a function of aciddissociation constants and hydrogen ion concentration :
2CO
α =
a2a1.
2
2
KKHKH
H
a1
-
3HCO
α =
a2a1.
2
a1
KKHKH
HK
a1
-2
3COα =
a2a1.
2
a2a1
KKHKH
KK
a1
Calculation from these expression
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Ca cu at o o t ese e p ess o
show the following
For pH significantly below pKa1,
CO2 is essentially 1
When pH = pKa1, CO2 = HCO3-
When pH = ½ (pKa1 + pKa2), HCO3- is at its maximum
value of 0.98
When pH = pKa2, CO32-
= HCO3-
For pH significantly above pKa2, CO32-
is essentially 1
The distribution of species diagram show that hydrogencarbonate (bicarbonate) ion is the predominant speciesin the pH range found in most waters, with CO2 predominating in more acidic waters
WATER ACIDITY
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WATER ACIDITYAcid-base phenomena in water involve loss and acceptance of
H+ ion.
An important species in the acid-base chemistry of water isbicarbonate ion, which may act as either an acid or a base
ACIDITY The capacity of water to neutralize OH-
Weak Acid (CO2, H2PO4-, H2PO4
-), protein, fatty acids, acidic
metal ions Fe3+
• Strong acids are the most important contributors to acidity
• The term free mineral acid is applied to strong acids such assulfuric acid and chloride acid in water
• Acid mine water is a common water pollutant that
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pcontains an appreciable concentration of free mineralacid
ALKALINITY
• The capacity of water to accept H+ ion (protons)
• Generally, the basic species responsible for alkalinity inwater are bicarbonate ion, carbonate ion, andhydroxide ion :
HCO3- + H+ → CO2 + H2O
CO32- + H+ → HCO3
-
OH- + H+ → H2O
The difference between pH and
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The difference between pH and
alkalinity• pH is an intensity factor, alkalinity is a capacity factor
Example : compare a solution of 1.10-3 M NaOH with asolution of 0.1 M NaHCO3
• NaOH is quite basic with pH of 11, but a liter of it will
neutralize only 1.10-3 mol of acid• pH of the NaHCO3 solution is 8.34, however a liter of
the NaHCO3 solution will neutralize only 0.1 mol of acid, therefore its alkalinity is 100 times that of themore basic NaOH solution
• In engineering term, alkalinity frequently expressed inunits of mg/L of CaCO3, based upon the reactions :CaCO3 + 2H+ → Ca2+ + CO2 + H2O
CALCIUM AND OTHER METALS IN
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U O S
WATERMetal ions in water solution are present in forms such as
the hydrated metal cation M(H2O)xn+
Metal ions in aqueous solution seek to reach a state of
maximum stability through chemical reactions :
Acid-baseFe(H2O)6
3+ FeOH(H2O)52+ + H+
Precipitation
Fe(H2O)63+
Fe(OH)3 (s) + 3H2O + 3H+
Redox
Fe(H2O)62+ Fe(OH)3 (s)+ 3H2O + e- + 3H+
Hydrated Metal Ions as Acids
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Hydrated Metal Ions as Acids• Hydrated metal ions, particularly those with a charge
of +3 or more, tend to lose H+ ion from the water molecules bound to them in aqueous solution, and fitthe definition of Brönsted acids, according to whichsare H+ donors
•
The acidity of a metal ion increase with charge anddecreases with increasing radius :
Fe(H2O)63+ FeOH(H2O)5
2+ + H+
CALCIUM IN WATER the highest concentration in most fresh-water system
a key element in many geochemical processes
mineral constitute the primary sources of calcium ion
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p yin waters :
# gypsum CaSO4.2H2O
# anhydrite CaSO4
# dolomite CaMg(CO3)2
Calcium ion, along with magnesium and sometimesiron(II) ion, account for water hardness
Temporary hardness is due to the presence of calciumand bicarbonate ions in water and maybe eliminated by
boiling the water :Ca2+ + 2HCO3
- CaCO3(s) + CO2(g) + H2O
HEAVY METALS
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HEAVY METALS• CADMIUM
• LEAD
•MERCURY
METALLOIDS
ARSENIC
In the earth crust 2-5 ppm
Formerly pesticide contain highly toxic arsenic compound such aslead arsenate, sodium arsenate, and cupper arsenate
Mine tailingproduced as by-product of copper, gold, and lead refining
ORGANICALLY BOUND METALS AND METALLOIDS
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ORGANICALLY BOUND METALS AND METALLOIDS
1. Those in which the organic groups is an alkyl groups
such as ethyl in tetraethyllead Pb(C2H 5)4
2. Carbonyl, some of which are quite volatile and toxic,
having carbon monoxide bonded to metals
:C O:
3. Those in which the organic groups is a electron
donor, such as ethylene or benzene