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ENVIRONMENTAL CHEMISTRY



ISTILAH TERKAIT

• Environmental Science

•

Ecology• Environmental Chemistry

• Toxicological Chemistry



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



What is Ecology ?

Ecology is the study of environmental factors

that affect organisms and how organisms

interact with these factors and with each

other



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



What is Toxicological Chemistry ?

Toxicological Chemistry is the chemistry of toxic

substances with emphasis upon their

interactions with biologic tissue and living

organisms



WATER, AIR, EARTH, LIFE &TECHNOLOGY



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



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



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



THE HYDROLOGIC CYCLE



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



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



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



The water molecule

Water dissolves many ionic compounds and salts that

do not dissolve in other liquids



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



THE CHARACTERISTICS OF BODIES OF WATER

SURFACE WATER occurs primarily in

STREAMS

LAKES

RESERVOIR

Stratification of a Lake

AQUATIC LIFE



AQUATIC LIFE

AQUATIC LIFE



AQUATIC LIFE

MAJOR AQUATIC CHEMICAL PROCESSES



MAJOR AQUATIC CHEMICAL PROCESSES



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



• [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



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



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



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



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



•The CO HCO CO 2- system in water may be



•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



These fraction designated as are given by the



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



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



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



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



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



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



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



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



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



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



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

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