Download Aquatic Chemistry (10 hrs)

Aquatic Chemistry (10 hrs)
Water
-The quality and quantity of water
available to human have been
vital factors in determining
their well-being.
-More then 70% of the earth is covered by
water. Living cells are 70% - 95% water
- In nature, water naturally exists in all three
physical states of matter -- solid, liquid, and gas
-Life absolutely depends on the properties of water.
-The structure of water is the basis for its unique
properties.
2
Molecular Structure of Water
O
• Water molecule is polar
H
+
H
+
Ability to form hydrogen bonds
-Hydrogen bonds are weak attractions between
the partially negative oxygen of one water
molecule and the partially positive hydrogen of a
different water molecule.
Hydrogen bonds can form between the water
molecules and fluorine, nitrogen, or oxygen atoms
on the solute molecule
Hydrogen bonds also
help to hold some
solute molecules
in solution.
What are
the
properties
of water?
Properties of Water
•
•
•
•
•
•
Excellent solvent
Cohesion
Adhesion
High Specific Heat
High Heat of Vaporization
Maximum density as a liquid at 4°C
Important properties of water
Excellent solvent
-Transport of nutrients and waste products
- Making biological processes possible in an
aqueous medium
Ionic and polar compounds dissolve in water
Water is a good solvent due to its polarity
Interacts with other polar compounds and
ionic compounds
Polar water
Molecules
surrounding
Na+ ions and
Cl- ions
THE CHARACTERISTICS
OF
BODIES OF WATER
Various bodies of water
Surface – Rivers, lakes, reservoirs, etc
Underground water- wells, etc
Sea water
Other sources of water- ice and snow,
water vapor in the atmosphere
rain
The water that humans use
is mainly,
- fresh surface water
- ground water
Thermal stratification in a non flowing water
body
Water’s unique temperature-density
relationship results in the formation of
distinct layers within non flowing bodies of
water
Thermal stratification in a non flowing water
body
Thermal Stratification in a non-flowing water
body
The disappearance of thermal stratification
causes the entire body of water to behave
as a hydrological unit, and the resultant
mixing is known as overturn.
Aquatic life (biota)
Autotrophic
Heterotrophic
Produces complex
organic compounds from
simple inorganic molecules
using energy from light
or inorganic chemical
reactions
Utilizes the organic
substances produced by
autotrophic organisms
as energy sources
Eg. Algae
Eg.Decomposes/reducers
(bacteria, fungi)
Productivity of a water body
The ability of a body of water to produce
living material is known as its productivity.
Eutrophication
A process where water bodies receive excess
nutrients that stimulate excessive plant
growth
Eutrophication of Lakes
--nutrient enrichment of
lakes mostly from
runoff of plant
nutrients (nitrates and
phosphates)
• -During hot dry
weather can lead to
algae blooms
• -Aquatic plants begin to
die
• -Drops DO levels
• -Fish die, bad odor
PHASE INTERACTIONS
CHEMICAL INTERACTIONS
INVOLVING SOLIDS,
GASES, AND WATER
CHEMICAL INTERACTIONS INVOLVING SOLIDS,
GASES, AND WATER
Some of these important interactions are;
* Production of biomass through photosynthesis in
algal cell.
• During this process dissolved solids and gases
exchange between cell walls and the water in
contact with the cells.
• Similar exchanges occur when bacteria degrades
organic matter.
* Processes that occur between sediment and
waters.
Gases in water
Gases in water
Dissolved gases—O2 for fish and CO2 for
photosynthetic algae —are crucial to the
welfare of living species in water.
The solubilities of gases in water are
described by Henry’s Law
Henry’s Law
At constant temperature the solubility of a
gas in a liquid is proportional to the partial
pressure of the gas in contact with the
liquid.
For a gas, “X,” this law applies to equilibrium
of the type
X(g)
X(aq)
William Henry
Mathematically, Henry’s Law is expressed as
Where,
[X(aq)] = aqueous concentration of the gas,
PX
= partial pressure of the gas,
K
= Henry’s Law constant (applicable to a
particular gas at a specified
temperature)
Carbon Dioxide in Water
-Carbon dioxide is only about 0.038% by
volume of normal dry air.
-The concentration of gaseous CO2 in the
atmosphere varies with location and season.
- It is increasing by about one part per million
(ppm) by volume per year.
-Rainfall from even an absolutely unpolluted
atmosphere is slightly acidic due to the
presence of dissolved CO2.
Carbon Dioxide in Water
-Carbon dioxide, and its ionization products,
bicarbonate ion (HCO3-), and carbonate ion
(CO32-) have an extremely important influence
upon the chemistry of water.
-The carbonate chemistry controls the pH of
water which is a master variable for many
geochemical processes.
The carbonate system is the major source of
buffering in the ocean
The CO2/HCO3–/CO32- system in water
The predominant species formed by CO2
dissolved in water depends upon pH
Substitution of the expressions for Ka1 and
Ka2 into the a expressions gives the fractions
of species as a function of acid dissociation
constants and hydrogen ion concentration:
The distribution of carbonate species as a fraction of
total dissolved carbonate in relation to solution pH
HCO3- is the predominant species in the pH
range found in most waters, with CO2
predominating in more acidic waters.
With this graph you can locate the fraction of
any of the required carbonate species at any pH.
The CO2/HCO3–/CO32- system in water
Determination of total dissolved inorganic
carbon (DIC) in a water body
CT
Aquatic scientists measure DIC most often by
acidification of water samples and subsequent
quantification of the extracted CO2 gas
Sediments
What are sediments?
Sediments are the layers of relatively finely
divided matter covering the bottoms
of rivers, streams, lakes, reservoirs, bays,
estuaries, and oceans.
Sediments typically consist of mixtures of
fine-, medium-, and coarse-grained minerals,
including clay, silt, and sand, mixed with
organic matter.
Formation of Sediments and
Its Importance
Importance:
Of particular importance is the transfer of
chemical species from sediments into aquatic
food chains.
Examples for sediment dwelling organisms
are various kinds of
shellfish (shrimps, crayfish, crab, clams) and
a variety of worms,
insects that are of particular concern because
they are located at the bottom of the food
chain.
Sediments may be formed by simple
precipitation reactions, several of which are
discussed below.
When a phosphate-rich wastewater enters a
body of water containing a high concentration
of calcium ion, the following reaction occurs to
produce solid hydroxyapatite:
Calcium carbonate sediment may form when water
rich in high level of calcium as temporary
hardness (loses carbon dioxide to the atmosphere)
Oxidation of reduced forms of an element can
result in its transformation to an
insoluble species,
Biological activity is responsible for the
formation of some aquatic sediments.
Some bacteria, including Ferrobacillus,
Gallionella, and some forms of
Sphaerotilus, utilize iron compounds in
obtaining energy for their metabolic needs.
These bacteria catalyze the oxidation of
iron(II) to iron(III) by molecular oxygen:
In anaerobic bottom regions of bodies of water,
some bacteria use sulfate ion as an
electron receptor,
whereas other bacteria reduce iron(III) to
iron(II):
The net result is a precipitation reaction
producing a black layer of iron(II) sulfide
sediment:
This frequently occurs during the winter,
alternating with the production of calcium
carbonate by-product from photosynthesis during
the summer.
Alternate layers of FeS and CaCO3 in a lake
sediment
Water Quality Parameters
Water quality parameters
1. Chemical parameters
-CO2, Alkalinity, DO, BOD, COD, pH, salinity,
other dissolved gases, hardness, etc.
2.
Physical parameters
-Temperature, transparency, turbulence,
conductivity etc.
3. Biological parameters
- microorganism content in
water, etc.
Alkalinity
-The capacity of water to accept H+ ions
(protons) is called alkalinity. (Alkalinity is a
measure of the capacity of water to neutralize
acids)
-Generally, the basic species responsible for
alkalinity in water are,
bicarbonate ion,
carbonate ion, and
hydroxide ion
-Higher alkalinity is associated with a body of
water’s ability to "soak up" proton without
altering the pH.
-Alkalinity prevents sudden changes in the
acidity level of water and, hence, is important
for fish and other aquatic life.
High alkalinity prevents wide pH fluctuations
Alkalinity
Following equation is the complete equation for
alkalinity in a medium where the only contributors
to it are HCO3-, CO32-, and OH-:
Method of Analysis
Alkalinity by this definition can be determined
by HCl titration of the water sample.
1. Phenolphthalein Alkalinity
A. Phenolphthalein indicator
B. pH 8.3 endpoint of titration
C. Measures Carbonates and Hydroxide ions
2. Total Alkalinity
A. Methyl Orange indicator
B. pH 4.3 endpoint of titration
Hardness
• Total hardness is primarily the total
concentration of metal ions (cations) in
water (mg/L), which includes mainly Ca2+ and
Mg2+
• Hard water” is generally associated with high
alkalinity
Alkalinity
CaMg(CO
CaMg
(CO3)2
Dolomite
2+
Ca
+
2+
Mg
+ 2CO3
Hardness
Hardness and Alkalinity Generally Go HandIn-Hand but They Are NOT One and the
Same
-Can have hard water and low alkalinity – water
high in CaCl2 and/or MgCl2
2-
Hardness
Temporary hardness
-Bicarbonates of Calcium and Magnesium
- This "temporary" hardness can be reduced
either by boiling the water, or by the addition
of lime (calcium hydroxide)
Permanent hardness
-Sulfates, chlorides of calcium and magnesium
- Cannot be removed by boiling
Effects of hard water
1. With hard water, soap solutions form a white
precipitate (soap scum)
A major component of such scum is calcium stearate,
which arises from sodium stearate,
the main component of soap
2 C17H35COO- + Ca2+ → (C17H35COO)2Ca
2. Hard water also forms deposits
that clog plumbing
Factors that affect pH
--Dissolved
CO2
-Bacterial activity
-Chemicals flowing into
the water body
-Sewage overflows
-Acid rains
-proteins, and fatty acids
-Acidic metal ions,
particularly Fe3+
Acid Rain
Acid rain is a rain or any other form of
precipitation that is unusually acidic,
meaning that it possesses elevated levels
of hydrogen ions (low pH)
• Even in the absence of air pollutants,
rain-water is slightly acidic (pH 5.6) due to
atmospheric carbon dioxide.
• This is due to air pollution by NOx and SO2
from vehicles and power plants.
.
Metal ions in water
Metal ions in aqueous solution exist as aqua
ions, where water molecules act as ligands,
and coordinate to the metal ion via the oxygen
donor atoms as shown for the [Al(H2O)6]3+
hexaaqua ion below:
Hydrolysis of metal aqua ions
The aqua ions undergo hydrolysis, to a greater or
lesser extent. The first hydrolysis step is given
generically as,
M(H2O)xn+ + H2O
[M(H2O)x-1(OH)](n-1)+ +H3O+
[
]
[
]
Metal aqua ions can act as Brønsted acids, which
means that they can act as proton donors.
Factors that control the acidity of
metal ions in aqueous solution:
-Metal aqua ions display varying pKa values
that are dependent on size and charge
-The higher the charge, the smaller the metal
ion
stronger the M-OH2 interaction.
Hydrolysis of metal aqua ions