The Water We Drink
Amal Lakany
Did you know that:
70% of the earth is water
50-65% of our bodies is water
75% of our brain is water
83% of our blood is water
90% of out lungs is water
22% of our bones is water
Water from tap or bottle?
There are 40 billion $ annual revenues
worldwide from the sales of bottled water
7.7 billion $ in USA
Consumption increased 11% in Europe
between 2001 & 2002
It is the highest selling among all
beverages
Although popular they are extremely
expensive: approximately 1000 times
more expensive than tap water
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Where does water come
from?
In atmosphere as:
vapor and tiny droplets in clouds
On earth as:
Underground aquifers (great pools of water
trapped in sand & gravel 50-500ft below
surface)
surface water in oceans, rivers, lakes,
ice..etc
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97.4% is salt water
2.6% is fresh water but mostly ice only
0.01% is rivers, lakes & streams
80% of this water is consumed in
irrigation and cooling electric power plants
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Water as a solvent
Solvent
Solute
Solution
Aqueous solution: a solution made from
water as a solvent.
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Solute concentration in
Aqueous solutions
Percent: 5% NaCl
Ppm or ppb analogyes
1ppm is 1 second to 12 days
1ppb is 1 second to 33 years or 1 inch to
the circumference of the earth
Molarity (M)= moles of solute/liter of
solution
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example
weighing paper.
1 M NaCl=
1mole NaCl/ 1L or
0.5 mole NaCl/ 0.5 L
etc.
Needed: volumetric
flask, balance, spatula
(a mole is the molecular wt. expressed in
grams)
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Water’s molecular str. &
physical properties
Water is 18 g/mol Liquid
N is 28 g/mol
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Gases
O2 is 32 g/mol
CO2 is 44 g/mol
Boiling point 100°C Freezing 0°C Expands when frozen
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Water’s molecular str. &
physical properties
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Water’s molecular str. &
physical properties
Electronegativity:
is the measure of
an atom’s
attraction for the
electron it shares
in a covalent bond
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When electrons are not equally shared, but
rather displace toward the more
electronegative atom the bond is said to be
a polar covalent bond
The higher () the E.N. difference the more
polar the bond the the intramolecular
force.
Molecules like Cl2 or H2 are non polar. This
depends on the geometry of the molecule
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Hydrogen bonding & its
role
An electronegative attraction between an
atom bearing a partial positive charge in
one molecule and an atom bearing a partial
negative charge in a neighboring molecule.
Leading to an intermolecular force i.e. a
force between molecules
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If it were not for this force water would have
boiled a -75°C
Hydrogen bonding is not restricted to water only,
but to any H2 atom connected to O, N, F
H-bonding is important in stabilizing proteins and
nucleic acids
DNA is stabilized by thousands of H-bonding it
plays an important role in life process
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ICE
LESS DENSE
than water
i.e.
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Being less dense as a solid makes it unique
in its characteristic:
Lakes freezes form top as ice floats on the
more dense water. Allowing life to continue
underneath
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Water boils at 100°C which is an
uncommonly high capacity to absorb and
release heat for such a small light
molecule.
This ability is expressed by specific heat
i.e. the quantity of heat energy that must
be absorbed to increase the temp of 1g of
a substance by 1°C. For water it s 1cal/g°C or
4.18 J/g°C
For this water has the highest specific heat
of any known liquid thus is used as a
coolant for our bodies, in electric plants,
the atmosphere around us
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Water as a Solvent
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Electrolytes: conducting
like NaCl solution
Non-electrolytes: non-
conducting solutions like sugar solutons
Ions: electrically charged species
that carry current in an aqueous
solution
Anions
Cations -vely charged
+vely charged Cl- in NaCl
Na + in NaCl solution
solution
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Ionic bonds: Na+Cl- (metals and non-metals)
Ionic compound: when elements from opposite sides of
the periodic table exchange electrons. E.g. Calcium chloride
Poly-atomic ions e.g. Na2SO4 → 2Na+ + SO42-
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Water solution of Ionic
Compounds
H2O
NaCl(s) Na+(aq) + Cl-(aq)
Na2SO4 ?
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Covalent compounds &
their solutions
Likes dissolve likes
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PCB & DDT are
non-polar would
dissolve in the fat
tissue of fish.
C2Cl4 used in dry
cleaning is a
carcinogen
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How to protect our drinking
water?
MCLG is the level, expressed in ppm or
ppb, at which a person weighing 70 kg
could drink 2L of water the contaminant
everyday for 70 yrs without suffering any ill
effects
MCL expressed in ppm or ppb sets the
legal limits for the concentration of a
contaminant.
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Treatment of municipal
drinking water
Passes through a screen to exclude large
objects
Add Al2(SO4)3 & Ca(OH)2
Al2(SO4)3 +3 Ca(OH)2 → 2Al (OH)3 + 3Ca(SO4)2
Gel settles filtered through gravel and then
sand
Disinfection by Cl2, NaOCl or Ca(OCl)2 to
produce HOCl of 0.075 -0.600 ppm remaining in
water
Other disinfectants could be ozone or UV
NaF could also be added
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Effects of dissolved
materials on water quality
How hard is your
water?
Hard water contains
high concentrations of
dissolved Ca & Mg ions in the
form of soluble HCO3- , Cl- ,
SO42-
Soft water contains few
dissolved Ca & Mg ions
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How hard is
the water?
EDTA2- is used to measure the concentration of Ca 2+
in water
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Ion exchange could
be used to remove
the hardness from
water. Zeolite is an
ionexchanger .
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Contaminates in Our Water
Natural contaminants in water include:
• Gases including radon, nonmetal
oxides, and others.
• Dissolved minerals including cations
and anions. Calcium, magnesium, and
iron salts cause hard water.
• Organic Matter: Bacteria,
microorganisms, and animal wastes are
all potential contaminants of natural
waters
Waterborne Disease
Contamination of water by
pathogenic organisms was a serious
problem. The environmental protection
agency (EPA) estimates that 30 million
people in the U.S. are threatened by
bacterial contamination of water supplies.
It is estimated that 80% of all illness in the
world is caused by water contamination.
Acid Rain
Sulfur and nitrogen oxides (SOx
and NOx) are deposited as acid rain.
Acidic precipitation damages the
environment by lowering the pH of
soil and lakes and streams
Sewage and Dying Lakes
The release of sewage into waterways
increases the biochemical oxygen demand
(BOD), and leads to eutrophication (aging)
of a lake. Organic matter can undergo either
aerobic or anaerobic decay
Eutrophication is a natural process that is
accelerated by the presence of human waste
and runoff from farms, lawns, and other
human activity.
Manufacturing processes produce waste
products and use water resources.
Groundwater Contamination
. Groundwater sources in many parts of the
country are contaminated. Groundwater is
easy to contaminate and difficult, as well as
expensive, to clean up.
Nitrates
Nitrate contamination of groundwater is
particularly a problem in rural areas. Agricultural
activity contributes fertilizers and animal wastes
to water sources. Nitrates are very soluble. They
are therefore difficult to remove from water
supplies. Nitrates are a problem with infants
usually less than one year old. They metabolize
nitrate to nitrite. Nitrite ions then complex heme
and the baby can turn blue and die. This condition
is known as methemoglobinemia (blue baby
syndrome).
Volatile Organic Chemicals
(VOCs)
VOCs can contaminate
groundwater and add undesirable odor
to drinking water. Also, many are
carcinogenic. Sources include:
industrial activity, oil and brine wells,
landfills, leaking underground storage
tanks, and illegal dumping of organic
wastes
Is there lead (Pb) in your
drinking water?
Sources of lead contamination
Old pipes, welding copper pipes, drinking
water fountains
Testing water for lead using
spectrophotometer
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Are there trihalomethanes
(THM) in your drinking
water?
Sources: HOCl + humic
acids→ THMs
Liver damage, cancer
Unavoidable especially with
surface water
Gas chromatography is used
to detect THM
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Desalination
Distillation is
expensive as a Reverse osmosis is used on
method of desilination riggs, shipps and in some
countries eg SA
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We Are the Solution to
Water Pollution
Water is essential to
our quality of life. We
must do what we can
to maintain the
quality of our water
sources.
