Chapter 13 Water: Rivers of Life; Seas of
Sorrows
Daniel Fraser
University of Toledo, Toledo OH
©2004 Prentice Hall
Chemistry for Changing Times 10th editionHill/Kolb
Chapter 13 2
Water
• Chemical formula: H2O
• 2/3 of human body is water– Similar salt concentration to the ocean’s
• Only substance to exist in all three phases on Earth
• Life as we know it is dependent on water
Chapter 13 3
Properties of Water
• All properties result from its shape
• Only common liquid on planet
• Expands when frozen– Solid less dense than liquid– Lakes don’t freeze solid during winter
• High density for liquids– Oil spills float. Do not sink
Chapter 13 4
Specific Heat
• Ability of 1 g of a substance to store heat
• Water has high specific heat– Acts as moderator of temperature– Do not get large temperature swings
• Land has low specific heat– Greater changes in temperature
Chapter 13 5
Heat of Vaporization
• Large amount of heat to vaporize a small amount of water
• Cool by evaporation– Sweating
• Land near bodies of water does have large temperature fluctuations
Chapter 13 6
Water Cycle• ~98% salt water; ~2% polar ice caps
<1% fresh water
Chapter 13 7
Natural Contaminants
• Gases: – O2 needed by aquatic life– CO2 produces acid rain
• Dissolved solids– Hard water: contains high amounts of Ca,
Mg, and Fe
• Organic matter– Dissolved decaying matter
Chapter 13 8
Chapter 13 9
Human Contamination
• May come from home, farm, or factory
• Wastes fall into two categories– Organic– Inorganic
• Most water contamination is local
Chapter 13 10
Waterborne Disease
• Microorganisms present in all water– Cholera, typhoid fever, dysentery– Kills about 25,000 people/day
• Requires chemical treatment to kill them
• 10% of world population has access to treated water
• Lessens recreational value of water
Chapter 13 11
Acid Rain
• Corrodes iron, limestone, marble• >1000 bodies of water are acidified• Kills by releasing metal ions into the
environment• Not a problem in areas where rock is
limestone– Neutralizes the acid
CaCO3(s) + 2 H+ Ca2+ + CO2(g) + H2O(l)
Chapter 13 12
Sewage
• Breakdown of organic matter requires O2
– Aerobic oxidation
• Deplete dissolved oxygen in water
• Measure amount of oxidation by using biological oxygen demand (BOD)– Higher BOD, greater amount of O2 required
and more oxygen depleted from the environment
Chapter 13 13
Eutrophication
• Increase BOD when algae bloom and then die off
• Natural phenomenon that can be accelerated by human wastes
• May cause streams and lakes to no longer harbor life
Chapter 13 14
• Release of a variety of different things when organic matter decays
• Depends on whether aerobic or anaerobic decay takes place– With or without O2
Chapter 13 15
Industrial Pollution• Requires lots of water to produce a car
Material Water required
(m3 water/ton of material)
Steel 100
Paper 20
Copper 400
Rayon 800
Aluminum 1280
Synthetic rubber 2400
Chapter 13 16
Groundwater Contamination
• Aquifer – source of underground water– Water pumped out for human usage
• Water may be contaminated– Some is natural
• Lots of groundwater in Bangladesh contains arsenic
– Contain industrial or agricultural contamination
• Once contaminated, hard to purify aquifer
Chapter 13 17
Some Groundwater Contaminants
• Nitrates, NO3–
• Come from fertilizers, decomposition of organic wastes, and animal feedlots
• Once present, difficult to remove
• Causes methemoglobinemia– Blue baby syndrome
Chapter 13 18
Volatile Organic Chemicals
• Also known as VOCs
• Add undesirable odor
• Many are suspected carcinogens
• Leached from buried dumps into aquifers – Very hard to remove
Chapter 13 19
Underground Storage Tanks
• Old service stations where gasoline is stored
• Last about 15 years
• Leak gasoline as well as any additives
• Must be dug up and disposed of properly
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Chapter 13 21
Concentrations of Pollutants• Typically given in parts per million, billion, or
trillion– ppm, ppb, or ppt
• ppm means 1 g solute per 1 million grams solvent
Chapter 13 22
Concentration Measurements
• Per Cent or Parts Per Hundred
• = mass of part / mass of whole X 100
• = mass of part / mass of whole X 102
• Parts Per Thousand
• = mass of part / mass of whole X 103
• Parts Per Million
• = mass of part / mass of whole X 106
Chapter 13 23
Concentration Measurements
• Per Cent or Parts Per Billion
• = mass of part / mass of whole X 109
• Parts Per Trillion
• = mass of part / mass of whole X 1012
Chapter 13 24
Concentration Measurements
• Mass of Part / Mass of Whole
• Numerator and Denominator Must be on Same Basis, e.g students/students, people/people, politicians/politicians, grams/grams, GRAMS/MILLITERS (special situation)
Chapter 13 25
Concentration Measurements
• Mass of Part / Mass of Whole
• 10 g / 100 g = 0.1
• 10 g / 100 mL = 0.1
Chapter 13 26
Concentration Measurements
• Mass of Part / Mass of Whole
• 10 g / 1 L = 10 g / ( 1 L X 1,000 mL / L)
• = 10 g / 1,000 mL
• = 0.01 (mass/vol.)
Chapter 13 27
Concentration Measurements
• Mass of Part / Mass of Whole
• 10 µg / 1 L = 10 µg / 1,000 mL
• = (10 µg X 1 g / 106 µg) / 1,000 mL
• = (10-5 g) / 1,000 mL
• = 10-8 (mass/vol.)
Chapter 13 28
Example 13.1 Contaminant ConcentrationsThe maximum allowable level of nitrate in drinking water set by the Environmental Protection Agency is 10 mg NO3
– per liter. What is this level expressed in ppm?
What is the concentration in (a) ppb and (b) ppt corresponding to a maximum allowable level in water of 0.1 µg/L of the gasoline additive MTBE (methyl tert-butyl ether)?
(0.1 µg X 1 g / 106 ) / ( 1 L X 1,000 mL / 1L) = 10-7 g / 1,000 mL = 10-10
Exercise 13.1A
To convert this nitrate level to ppm, we need to have the numerator and denominator in the same units. By using m.illigrams, we make the denominator 1 million mg. The numerator then expresses the ppm of olute, that is, ppm NO3
–
10 mg NO3–
1000 g water
1 g water
1000 mg water
10 mg NO3–
1,000,000 mg water= 10 ppm NO3
–=x
What is the molarity of the solution in Part A? CH3-O-C(CH3)3 Form. Wt. = 88 g/mol
M = moles / Liter = (10-7 g / 88 g/mole)/ 1 L = 1.14 X 10-9 M
Exercise 13.1B
Chapter 13 29
Water Purification
• Remove dirt and most bacteria by filtration
• Aerate water– Otherwise tastes flat
• If necessary, filter through charcoal– Remove colored or odorous compounds
• Kill remaining bacteria
Chapter 13 30
Chemical Disinfection• Chlorine
– Inexpensive and effective– Any remaining chlorine will kill microorganisms
between water plant and house– May impart taste to water
• Ozone– More effective than chlorine– More expensive– No residual protection
Chapter 13 31
Chapter 13 32
New Technologies for Water Purification
• Ultraviolet light– Kills bacteria– Effective for small-scale applications– No chemical residue
• Ultrasound– Tuned to produce reactive species in water– Kills bacteria– No chemical residue
Chapter 13 33
Fluoride
• Added to water to prevent tooth decay– In areas where used, cavities decrease by up
to 65%
• Makes tooth enamel harder
• Typically between 0.7–1.0 ppm
• In high concentrations, may cause mottling of tooth enamel
Chapter 13 34
Wastewater Treatment• Primary sewage treatment
– Removes some solids– Has large BOD
Chapter 13 35
Secondary Sewage Treatment
• Pass material from primary sewage treatment through sand filters
• Also some aeration to decrease BOD– Allow aerobic bacteria to work
• Typically have both primary and secondary sewage treatment for wastewater
Chapter 13 36
Activated Sludge Method
• Combination of primary and secondary wastewater treatment
• Sludge must be disposed of
Chapter 13 37
Other Treatments
• Charcoal filtration: absorbs organic molecules– Charcoal must be replaced periodically
• Reverse osmosis: force water through semipermeable membrane– Requires high pressures– Expensive
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Chapter 13 39
Bottled Water
• Increased usage because of perception that bottled water is safer– Less rigorous testing of bottled water vs. tap water
• 25% of bottled water comes from municipal water supplies
• May have more dissolved ions than tap water
Chapter 13 40
Water Usage• Americans use a lot more than they think
• Try to conserve water at all times
Chapter 13 41
End of Chapter 13
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