Module 2 Flashcards
Define: Dipole
A molecule with two poles, one positive and one negative
Hydrogen bonding
strong type of intermolecular dipole-dipole attraction. Occurs between hydrogen and F, O or N (molecules with lone pair electrons)
Describe the molecular structure and size of water
Bond angles of 105 degrees with an electronegative side on the oxygen and an electropositive side on the hydrogens
Key properties of water
Dipolar- facilitating interactions with other dipoles or charges molecules (ions);
Hydrogen bonding- leading to high density (1 g /mL, highest density at 4 degrees), cohesiveness, high boiling point and surface tension (water clusters together);
transparent to visible and UV light- allows light for photosynthesis to penetrate water bodies to considerable depth;
very polar- allowing for the ability to hydrate ions, a good solvent for ions, most important / abundant solvent on earth;
High heat capacity- cp = 4.1855 Jg^-1K^-1, temperature stabilization of organisms / geographical regions, water used for AC chillers, nuclear power plants, etc;
High surface tension- ~73 mN/m (organic solvents 18-33 mN/m)
Define: Water (aqueous) chemistry
the study of chemical reactions and processes affecting the distribution and circulation of chemical species in natural waters
What can water dissolve?
Inorganic molecules- Salts that dissociate to anions and cations (ie. CO3(2-), Ca(2+), Cl(-), Mg(2+)
Organic molecules- Natural organic matter (ie. decaying leaves), pollutants (ie. pesticides, PAHs, estrogen disruptors)
Dissolved gases- Oxygen and Carbon dioxide
Biological Microorganisms- Bacteria and viruses
How is water distributed on earth?
Polar Ice Caps: 1.7%
Oceans: 97.5%
Fresh Water: 0.77%
Describe the water cycle
Global pools include oceans, ice, groundwater, lakes and rivers and clouds. The water circulates between pools through condensation, precipitation and evaporation. Water is also impacted by the anthrosphere through municipal and industrial use.
What molecule has a significant effect on water pH?
Increase in sulfate causes a significant decrease in pH
What size of molecules are considered to be POC domain? DOC domain?
POC = greater than 1 microm (contains bacteria, protozoa, phytoplankton, zooplankton)
DOC = less than 1 microm (contains viruses, humic acids, etc.)
When did water usage stabalize in the US?
1985
What is the primary use of water in terms of anthropogenic use?
Electric power generation
Define Point sources of pollution
Sources which emanate from a single point (wastewater treatement plant, industry)
Define: nonpoint sources of pollution
land areas such as fields roads and parking lots that generate surface runoff containing various types of contaminants
Describe the physical characteristics of water
- Temperate - pH, density, dissolved gases
- Turbidity - measure of water clarity. Affected by suspended solids and coloured material
- Colour - due to dissolved substances
- Taste and odor - organic (bacterial degredation, of algae and algal waste products) and inorganic compounds in water (ferrous, manganous and sulfide ions and chlorine)
- Solids content - Total solides refer to material left in a dish after a water sample is evaporated and dried
Describe the different types of solids in water
- Dissolved solids - refer to material that pass through a standard glass-fibre filter
- Suspended solids - refer to material retained by a standard glass-fibre filter
- Volatile solids - refer to material lost when dried solids are burnt organic material -> CO2
- Fixed solids - Refer to material retained when dried solids are burnt
How do you calculate total solids?
mg/L total solids = (mg of dried residue)/ (L of sample)
Describe the chemical characteristics of water
- Salinity (dissolved solids) - measure of salts in water usually expressed in ppm (mg/L). A result of the polarity of H2O, increasing the ability to hydrate ions, and a good solvent of ions. Many rocks weather and disolve, changing the salinity of the water
- Hardness - Hardness index = ([Ca(2+)]+[Mg(2+)]) * MW (CaCO3)
- Dissolved gases (oxygen and CO2) - critical for living species in water (esp. O2 and CO2). The amount that a gas dissolved in water is calculated by Henry’s Law. Stratification has a significant effect on the system
- Biochemical Oxygen Demand (BOD) - the amount of oxygen required by microorganism to oxidize dissolved organic matter in water samples. Calculated by letting water sit for an extended amount of time, where a big change in DO indicates a large BOD
- Chemical Oxygen Demand (COD) - The amount of ocygen consumed as a result of oxidation (by dichromate, a powerful oxidizing agent) of dissolved organic matter (and other oxidizable components) in the water
- Total organic carbon (TOC) - calculated from non-filtered samples, while dissolved organic carbon calculates from filtered samples. Measured through a TOC analyzer. An Important parameter for both drinking water and wastewater treatment. Also includes dissolved oxygen carbon which is removed through filtered samples
- Alkalinity
- pH
Describe the implications of lake stratification in chemistry
Epilimnion has a realatively high dissolved O3, chemical specieas in oxidized forms as photosynthesis > than respiration
Hypolimnion has relatively low dissolved O2, chemical species in reduced form, there is exchange of chemical species with sediments
What factors affect dissolved oxygen (DO)
- Temperature - solubility of gases in water decreases with increasing temperature
- dissolved O2 is consumed by the degredation of organic matter in water
- Overturn causes the chemicals in lakes to mix, changing the
- Photosynthesis and respiration in aquatic organism
What are the conditions of aerobic water?
describe the molecules present and the electron activity
CO2, SO4-, H2CO3, HCO3-, NO3-, Fe(OH)3 are present with a high pE value; oxidizing environment
What are the conditions of anaerobic water?
CH4, H2S, NH3, NH4+, Fe(2+) are present; low pE values and a reducing environment
Define pE
The degree to which a water is oxidizing or reducing depending on the solute species present, reflecting the activity of the electron, e-
describes the availability of electrons in solution
is analogous to teh concept of pH
Describe carbon chemical transformations in the hydrosphere
Photosynthesis: CO2 + H2O + hv -> {CH2O} +O2 (g)
Biochemical oxidation of biomass, {CH2O}:
{CH2O} + O2 -> CO2 + H2O
Describe the Nitrogen chemical transformations in the hydrosphere
Nitrogen fixation: 3{CH2O} + 2 N2 + 3 H2O + 4H+ -> 3 CO2 + 4 NH4+
Nitrification: 2 O2 + NH4+ -> NO3- + 2 H+ + H2O
Denitrification: 4 NO3- + 5{CH2O} + 4 H+ -> 2 N2 + 5 CO2 + 7 H2O
Describe the Sulfate chemical transformation in the hydrosphere
Sulfate reduction: SO4(2-) + 2 {CH2O} + 2 H+ -> H2S + 2 CO2 + 2 H2O
Sulfate Oxidation: H2S +2 O2 -> 2 H+ + SO4(2-)
What are the biological characteristic of water?
- Biological Microorgamisms- Pathogenic (including bacteria, protozoa, viruses, helminths); Non-pathogenic (including algae and fungi, non-pathogenic bacteria)
What are the potential consequences of pathogenic microorganisms in water?
Infectious disease: Fecal-oral route, disease passed from feces of a hot to the mouth of another; usually indirect route via contaminated water and food; can be from viruses, bacteria and / or protozoa. We need a different amount of each virus / bacteria / protozoa for it to be infectious
Describe pathogen testing and why it can be challenging
Challenges:
1. Present in low numbers,
2. limited survival time
3. numerous pathogens to analyze
4. time and cost prohibitive
Pathogens are normally monitered based on indicator organisms, which help us better understand if there are pathogens in the water
Describe the Ideal characteristics of an indicator organism
- present when pathogens are in the water
- absent in non-contaminated water
- present in higher numbers than pathogens in contaminated water
- easy to analyze
ie. coliform bacteria as an indicator of E. Coli
How does pH work in water?
Water auto-ionizes with dissociation constant @ 25 degrees: 2 H2O <-> H3O+ + OH-
Kw = 1.008 x 10^(-14) = [H3O+] x [OH-]
[H3O+] = [OH-] = 1.0 x 10^(-7) mol x L ^(-1)
pH = -log [H3O+]
pH = 7.0
Kw changes with temperature (all equillbrium constants are affected by temperature)
The neutral pH changes for different temperatures
Neutral pH at 15 degrees C is 7.18 not 7.0
What are the major components of the carbon cycle?
Photosynthesis - Atmospheric CO2 is tranferred to biosphere (plants) by photosynthesis and covnert it to biomass
Biodegradation - Plants and living organisms die and becom humic carbon in dirt and soil
Respiration - Animals also produce CO2 to the atmosphere by respiration
Atmospheric CO2 - absorbed to surface water and oceans to form bicarbonate and carbonate
Minerals and Rocks - carbonates in water in the presence of Ca2+ can precipitate to for CaCO3 (limestone) and other rocks. Limeston can also dissolve to form carbonates in water
Fossil Fuels - Human economic activities (burning of carbon-containing fuels) also contribute ot the release of CO2 to the atmosphere
What chemical equation describes photosynthesis
CO2 + H2O + hv -> {CH2O} + O2
What chemical equation describes biodegradation?
5 {CH2O} + 4 H3O+ + 4 NO3- -> 2 N2 + 5 CO2 + 11 H2O
2 {CH2O} + H3O+ + SO4(2-) -> HS- + 2 CO2 + 3 H2O
2 {CH2O} -> CH4 + CO2
What chemical equation describes respiration
{CH2O} +O2(g) -> CO2 + H2O
What chemical equations describe atmospheric carbon absorption?
H2CO3 <-> HCO3- + H+; K2 = 4.3x10^(-7)
HCO3- <-> CO3(2-) + H+; K3 = 4.7x10^(-11)
What chemical equation describes the interactions of minerals and rocks with water?
CaCO3 +CO2 + H2O -> CO2 + H2O
Describe the interactions of carbonate species in water, air and rock, soil and sediments
CO2(g) <-> H2CO3; as per Henry’s Law btwn air and water
CaCO3(s) <-> Ca 2+ + CO3 (2-); as per Ksp btwn rocks and water
CO3(2-) + H2O <-> OH- + HCO3-; acid base reaction in aq
H2CO3 <-> H+ + HCO3-; acid base reaction in aq
The carbonate species in water are CO3(2-), HCO3- and H2CO3
What is the rate of dissolution of carbon dioxide?
CO2(g) <-> CO2(aq) H = 3.4x10^(-2) Atm^(-1)
H2CO3 <-> HCO3- + H+ Ka1 = 4.3 x 10^(-7) M
HCO3- <-> CO3(2-) + H+ Ka2 = 4,7 x 10^(-11) M
How does carbonate species present reflect the pH
< pKa 1 (pH = 6.3); [H2CO3] > [HCO3-]
pka = 1 (pH = 6.3); [H2CO3] = [HCO3-]
between pKa 1 - 2 (pH 6.3 - 10.6); [H2CO3] < [HCO3-] < [CO3(2-)]
pKa = 2 (pH =10.6); HCO3- = CO3(2-)
> pKa2 (pH > 10.6); [CO3(2-)] > [HCO3-]
Why is the ocean pH <8.7
- Temperature gradients and stratification
- Deposition of acidic compounds (south america, saudi arabia)
- Presemce of other “buffers” (ie. silica, CaSO4)
- non-equilibrium: ocean not wel mixed
Define Alkalinity
a measure of the capacity of water to neutralize a strong acid. In natural waters: HCO3-, CO3(2-), OH; borates, ammonia, phosphates, organic bases, organic matter (in low concentration)
