Transcript WATER: Properties and Issues

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The Wonders of Water
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American Chemical Society
Wondering About Water
Interesting facts about Water
 Over 70% of the Earth’s surface is covered with this
liquid (oceans, rivers, lakes, etc.)
 The second most common form of water on Earth is
ice (if all the ice melted – the sea-level would rise by
70 meters)
 Water is essential for life (most animals and plants
contain more than 60% water by volume).
 Less than 1% of all water on Earth is available or
clean enough for humans to drink. The rest is salty or
frozen.
Some of Water’s Physical
Properties
 Boiling Point = 100 ⁰C (212 ⁰F) at 1 atmosphere of
pressure
 Freezing Point = 0 ⁰C (32 ⁰F) at 1 atmosphere of
pressure
 Density = 1 g/cc (at 4 ⁰C)
 Nearly Colorless
 Tasteless
 Odorless
The Structure of Water – H2O
Image from:
http://www.chem1.com/acad/sci/aboutwater.html
A Chemical Description of
Water
 One atom of oxygen (O) is bound to two atoms of
hydrogen (H) to form a 105 ⁰ angle “V” shape.
 Both H atoms are attached to one side of the O atom.
 This results in a molecule with a slight positive charge
on one side of the molecule (H) and a slight negative
charge on the other side (O) – this is called a dipole
moment.
 Thus, water molecules tend to attract each other by a
process called Hydrogen-Bonding - this gives water
many unique properties.
Hydrogen Bonding – creates
attraction between water
molecules
Image from:
http://commons.wikimedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.jpg
Unique Properties of Water
 The only natural substance found as a liquid, solid,
and gas at temperatures normally found on Earth
 Part of every living organism
 It dissolves nearly everything (universal solvent)
 It can absorb large amounts of heat – heat exchange
between the atmosphere and oceans contribute
greatly to Earth’s weather
 It’s molecules stick together to form beads or drops
(high surface tension) – for example, rain drops
Water Exists Primarily in Three
States; Liquids, Solids, and
Gases
Image from:
http://apollo.lsc.vsc.edu/.../chapter2/lat_heat3.html
Another Unique and
Important Property
 Most liquids contract when they get colder.
 Water contracts until it reaches 4 ⁰C . Then it expands
until it is solid.
 The density of ice (0.915 g/cc) is less than that of
liquid water (0.9999 g/cc) at 0 ⁰C.
 Its density at 4⁰C is 1.000 g/cc.
 This is why ice floats – if it didn’t, oceans, lakes, etc.
would freeze from the bottom up and remain frozen –
Earth would be a completely different planet - maybe
uninhabitable by humans.
American Chemical Society
Water Matters
Overview
 The amount of available water has not changed for
thousands of years.
 Water is essential to the environment, human life, and
industry.
 Approximately 1 billion people in over forty countries
are currently under a water crisis.
 The increasing world population and the demand for
better livelihoods globally, will continue to contribute to
a worsening water crisis.
Source: World Bank “Water and Development” Executive Summary, May
2010
Scarcity of Resource
 Each year millions of people die from diseases
associated with inadequate water supply, sanitation
and hygiene.
 Four of every ten people in the world do not have
access to adequate sanitation.
 Two of every ten people have no source of safe
drinking water.
 According to the United Nations World Water
Development Report, by the year 2050, at least one in
four people is likely to live in a country affected
recurring shortages of freshwater.
Source: http://www.un.org/waterforlifedecade/background.html
Did You Know?
 Every day, 2 million tons of sewage and other
types of pollution drain into the world's waters.
 Every year, more people die from unsafe water
than from all forms of violence, including war.
 The most significant sources of water pollution
are lack of effective management and poorly
treated human, industrial, and agricultural
wastes.
Source: http://www.un.org/waterforlifedecade/quality.html
Pollution
 Pollution refers to the introduction of harmful substances or products into
the environment.
 Major water pollutants include microbes, nutrients, heavy metals, organic
compounds, oil, sediments and heat (thermal pollution*). * Thermal
pollution is typically the industrial release of heated water into a river, lake,
or other body of water, causing a rise in temperature that endangers
aquatic life
 Pollutants are usually the cause of extremely dreadful water quality
conditions around the world..
Source: World Water Development Report 3 'Water in a Changing World'
http://www.un.org/waterforlifedecade/quality.html
Analyzing Water
 Depending on its use, water may have a variety of conditions for
composition and purity.
 Types of analysis vary from simple field testing to determine a
single property to laboratory based multi-property analysis.
 Some basic water quality measurements include pH, Acidity,
Alkalinity, electrical conductivity, and water hardness.
 The pH of water measures its hydrogen ion concentration and
indicates whether the sample is acidic, neutral or basic.
 Acidity of water measures its capacity to react with strong base to a
designated pH.
 Alkalinity measures the acid-neutralizing capacity of water. It is
attributed to the presence of hydroxide, carbonate, and bicarbonate
ions.
American Chemical Society
Water: Getting It Clean,
Keeping It Clean
Potable Water and Its
Importance
Water is considered potable if it is safe for drinking
and food preparation.
http://en.wikipedia.org/wiki/File:Water_quality.jpg
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Characteristics of Potable
Water
 To be safe, drinking water must have minimal
(safe) levels of the following:
Disease causing microorganisms
 Cost to remove: low
Dissolved chemicals
 Dissolved solids (salts that produce ions when dissolved)
 Toxic organic compounds
 Cost to remove: high to very high
Suspended solids
 Cost for removal: low
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Freshwater Sources
 Most public water sources are based on the low cost
removal of suspended solids and microorganisms.
 Therefore, the water used in drinking water treatment
plants must be fresh, meaning that it contains safe
levels of dissolved chemicals.
 Sources of Freshwater
 Surface water: rivers, lakes, reservoirs, springs, etc.
 Ground water: wells
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Public Drinking Water Treatment
 Prechlorination and aeration
 Prechlorination controls microbes such as algae that can clog a
water treatment facility.
 Aeration converts iron and manganese to insoluble forms that can
be removed.
 Coagulation (flocculation): conversion of small suspended
particles (colloids) by causing them to aggregate into
larger clusters.
 Usually encouraged by addition of a chemical flocculating agent
such as alum (KAl(SO4)2.12H2O).
 Disinfection – remove microorganisms
 Chemical Methods: chlorine, ozone, chlorine dioxide
 Ultraviolet light, sunlight
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Public Drinking Water Treatment
(cont.)
 Sedimentation: allowing larger particulates and “floc” to
settle out by gravity.
 Filtration: removal of additional particulates by passing
water through filter.
Sand is often used as a filtration medium
A layer of activated carbon or anthracite coal can be
added to remove dissolved organic materials.
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Public Drinking Water Treatment
Diagram
http://www.americanchemistry.com/s_chlorine/docs/images/water_treatment.gif
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Public Wastewater Treatment
(Sewage Treatment)
 Pretreatment
Debris Screening: large objects like wood, paper,
toys, etc. are removed.
Grit removal: large particles like sand and coffee
grounds removed.
 Primary Treatment: Sedimentation:
Fine particulates removed from tank bottom
Oil and Grease can be skimmed off top
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Public Wastewater Treatment
(Sewage Treatment - Cont.)
 Secondary treatment
Removes dissolved and suspended biological
material
Often utilizes trickle tanks that contain affixed
microorganisms that digest biological material.
 Tertiary treatment:
Disinfected
Other
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Public Wastewater Treatment
(Sewage Treatment Figure)
http://www.gic-edu.com/uploads/wastewatertreatment.jpg
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Protecting Freshwater Sources
It is important that everyone take responsibility for
protecting our freshwater resources.
 Conserve water in our homes
 Avoid disposing of the following in sewer system
 Medications
 Grease and oil
 Pesticides
 Automotive and other chemicals
 Limit non-point source pollution: chemicals released in
the environment at large that get washed into rivers,
lakes, etc. by rainfall.
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Summary

Over 70% of the Earth’s surface is covered with this liquid (oceans, rivers, lakes, etc.)

Water is essential for life (most animals and plants contain more than 60% water by volume).

One atom of oxygen (O) is bound to two atoms of hydrogen (H) to form a 105 ⁰ angle “V”
shape.

Thus, water molecules tend to attract each other by a process called Hydrogen-Bonding - this
gives water many unique properties.

The amount of available water has not changed for thousands of years.

Approximately 1 Billion people in over forty countries are currently under a water crisis.

The most significant sources of water pollution are lack of effective management and poorly
treated human, industrial, and agricultural wastes.

Some water quality measurements include pH, Acidity, Alkalinity, electrical conductivity, and
water hardness.

Freshwater is a valuable resource that should be protected.

Most freshwater must be treated before it is safe for drinking and food preparation.

Methods for preparing potable water have to be adapted to each specific situation

Methods such as desalination or atmospheric water harvesting are being developed and
advanced to augment supplies of freshwater in the future.