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Environmental Chemistry > Exam 1 (ch 10, 11, 12, 13) > Flashcards

Exam 1 (ch 10, 11, 12, 13) Flashcards

1
Q

Uses for water

A
  • drinking
  • cleaning
  • agriculture
  • waste water
  • industry cooling
  • recreation
  • wildlife
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2
Q

Speciation

A
  • chemical species - structurally specific form of a chemical
  • multiple forms that a chemical can take
  • large molecules may be heavily effected by functional group speciation
  • evaluate small changes between structures
    • ligand binding
    • protonated/deprotonated
    • oxidation state (redox reactions)
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3
Q

Effect of Speciation

A
  • Some ox. states are toxic and others are not.
  • Free metal (2+) is typically most toxic
  • different environmental interactions
  • change in charge
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4
Q

Free Ion Activity Model

A
  • free metal is actually M(H20)6 2+
  • octahedral
  • aquo species
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5
Q

Sources of Metal in Aq. System

A
  • natural weathering of minerals and soils
  • background metal concs are not zero
  • enhanced by human activities (mining, construction)
  • rapid exposure of minerals to oxygen and water
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6
Q

Anthropogenic sources

A
  • originating from human activity
  • point sources - “end of the pipe”, mining, smelting, manufacturing
  • nonpoint sources - diffuse, landscape level contributions
  • Zn from tires and Cu from brakes are nonpoint sources
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7
Q

Receiving water

A

any body of water that gets input of material from human activities

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8
Q

Metal Tox in Aquatic Systems

A
  • related to impacts on gills (like human kidney)
  • responsible for respiration and ion regulation (osmoregulation)
  • Cu tox in aqua is 10-100 ug/L drinking water tox is 3mg/L
  • biotic ligand is the target of metal
  • metal bind to ion transport protein, has higher affinity than major ions (Ca, K, Mg, Na)
  • Eq. process so LeChatelier’s principle applies
    • competing constituents for metal can effect eq.
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9
Q

Biotic Ligand Model

A
  • predicts site specific water quality
  • effects:
    • pH
    • species with lone pairs
    • DOM (functional groups)
  • total amount of metal in water is NOT a good indicator of tox.
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10
Q

Complex equilibrium

A
  • common central species “parent material”
  • parent material has relatively low conc compared to ligand conc.
  • ligands are the “controlling variables”
    • conc is environmentally controlled. varies by location
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11
Q

Complex equilibrium steps

A
  • write all stepwise, one ligand exchange at a time
  • write overall. one reaction with all ligands to make product (beta equil constants)
  • write mass balance equation
    • algebraic rearrangement. betas, controlling variables and parent material
  • alpha expressions. ax = x/CT
  • [x] = alphax (CT)
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12
Q

Environmental Redox

A
  • natural systems - environment controls ox and red
    • env. controls one half of the redox reaction
  • Aerobic vs anaerobic
  • O2 is dominant oxidizing agent

O2 + 4H + 4e = 2H2O

  • other element for oxidation half reaction
  • aerobic environments likely for oxidation to occur
    • more oxidized speciation of element is more likely
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13
Q

Redox in Anaerobic

A
  • O2 is absent
  • wetlands (swamps), deep sediment, intestinal tract
  • saturated with water, high microbe activity, no sunlight, light organic matter
  • microbes consume oxygen during respiration
    • {CH2O} + O2 = CO2 + H20
  • oxygen diffusion in air is faster than in water
  • influenced by relative rates - O2 can diffuse in water, but may be consumed faster
  • sand/soil without microbes can be aerobic for 10s of meters
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14
Q

Anaerobic Microbial Activity

A
  • when O2 consumption > O2 diffusion
  • anaerobic respiration is less efficient than aerobic metabolism
  • less activity leads to more organic matter accumulation
  • {CH2O} = CO2 + 2H
    • Carbon from 0 to 4+ ox state
    • other element in environment will be reduced
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15
Q

Microenvironments

A
  • inorganic will have less microbes and more O2
  • organic matter will be home to microbes and less O2
  • can change from aerobic to anaerobic within mm of soil
  • organic matter zone could cause anaerobic zone
  • soil is heterogeneous
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16
Q

Soil solution

A

-centrifuge water out of soil

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17
Q

Soil/Water levels

A
  • soil surface
  • water table (unsaturated)
  • groundwater (saturated pores)
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18
Q

Measuring Redox

A
  • redox potential measure:
    • electrochemical cell in lab
    • environmental water sample
      • surface water
      • soil solution
      • groundwater
  • Electrode
    • inert material
    • reference electrode, calomel electrode (Hg/Hg2Cl2)
    • correct measurement to standard hydrogen electrode
    • Estd = Ecal +0.242V
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19
Q

pE

A
  • conceptual representaion of the tendency for a system to donate or accept electrons
  • not real measurement, but conceptual representation
  • pH = -log ae
  • ae is the activity of electrons
  • pE ranges from -12 to 25. Lower values indicate high ae and reducing conditions
  • high pE is lack of electrons
  • based on stability of water. Cannot get so high or low that water is ox or red
    • dependent on pH
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20
Q

Water red and ox

A

oxidation - 6H2O = 4H3O+ + O2 + 4e

reduction - 2H2O + 2e = H2 + 2OH-

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21
Q

Pourbaix Diagram

A
  • speciation according to redox potential and pH
  • whole diagram is equil conditions
  • equal conc on species lines
  • vertical lines are acid base reactions
  • horizontal lines are redox reactions
  • further away from line, more dominant species in the center. Other species are NOT absent
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22
Q

Acid Volatile Sulfides

A
  • model to predict metal toxicity in sediments
  • based on affinity of transition metals for sulfide (Kf)
  • formation constant is the inverse of the solubility constant
  • MS is not biologically available for uptake so no toxicity effect. Free ion most toxic
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23
Q

AVS solubility products

A

H2S = H+ + HS-

HS- = H+ + S2-

Ksp based on following reaction:

MmSn + 2H+ = mM+ + nH2S

  • dependent on pH
  • more acidic, more soluble metal sulfides, more free metal ions
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24
Q

AVS species

A
  • most Sulfide (S2-) is bound to Fe2+. FeS
  • FeS serves as reservoir
    • Stronger competition will replace Fe.
    • K of replacement reaction is product of reactions
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25
Metal Speciation in Sediments
* can change based on environment * Sulfite has high affinity for thiol groups on cistine * Metal ion interaction with functional groups ins exchangable * adsorbed - exchangable, carbonates, Fe and Mn oxides * Extract w/0.5M HCl - absorbed fractions and M sulfides * other fractions include organic matter and residual * residual - in the particle, not coming out * adsorbed - on the surface
26
AVS extraction
* FeS and MeS - molar total gives AVS * Simultaneously Extracted Metal (SEM) - Me2+ when HCl dissociates MeS and FeS * Add HCl and condense H2S volatile gas
27
Normalized Toxicity
* cant impact tox based on total metal * normalize using mol SEM/AVS * SEM is potentially bioavailable * AVS - sulfide is available to complex metal ions * When SEM/AVS \< 1 then little free metal * metal titration used to determine how much metal is dissolved when an amount of cadmium is added
28
Assimilative Capacity
- amount of a contaminant that can enter the environment w/o causing significant changes - increased AVS increases capacity
29
AVS evaluation
* evaluate ratio of SEM and AVS * SEM/AVS \<1 then metal
  • SEM/AVS >1 then metal>sulfide, free metal present
  • limiting reagant problem
    •
    30
    Dissolved Gas Importance
    * habitat quality (O2) * greenhouse gas emissions (CO2, CH4, N2O) * contaminant distribution * gasoline between water table and groundwater some equil and dissolves into watertable and groundwater
    31
    Simple and Reactive gases
    * simple - no reaction between gas and water as it dissolves * reactive - gas reacts with water * CO2 + H2O = H2CO3
    32
    Henry's Law
    * simple gases * valid for low conc such as environmental * equil of dissoved and gas phase * [G] = KHPG * PG : partial pressure of gas * watch the units * Temperature effects solubility. KH is only valid at one temp. * solubility decreases as temp increases
    33
    PO2 * PO2 = PdryXO2 * Pdry = Patm - PH2O * Pressure of water is highly variable * Atmospheric O2 is typically 20.9%, 2.04e4 Pa * [O2] = KH (2.04e4 Pa) = 2.7e-4 M * normally expressed as 8.5 mg/L * can range in waters from 5 - 14 mg/L * Assuming at equil
    34
    Gas in Water Equil Assumptions
    * sink - consumes the species * aerobic metabolism decreases O2 * CH2O + O2 = H2O + CO2 * source - produces the species * photosynthesis * 6CO2 + 6H2O = C6H12O6 + 6O2 * Compare relative rates of sink and source
    35
    Time of day effect on O2
    * day time plants net produce O2 * night time plants net consume O2 * Highest O2 levels in afternoon/evening * Lowest O2 levels in early morning * At equil with the atmosphere twice per day
    36
    Physical Processes effect on Gas/Water Equil
    * effect mixing/diffusion * boundary layer - between the bulk air and fluid water * faster the flow, the thinner the boundary layer * aeration - increase surface area and increase flow (physical mixing) * rainwater and atmosphere are a good equil assumption * limited bio process (no sink or source) * small volume compared to surface area
    37
    Special Circumstance Gas/Water Equil
    * when gas phase is NOT the bulk atmosphere * closed container * soil pore spaces * In these cases equil assumption can be made and we can use Henry's law to _assess_ the equil
    38
    CO2 in Water
    * resultant species: CO2(g), CO2(aq), H2CO3, HCO3-, CO3 2- * Can increase overall aq concentrations * Environment can control aq. speciation * pH as controlling variable * CO2 can affect environmental pH
    39
    Atmosphere controls speciation
    * poorly buffered water then CO2 can control pH and conc of HCO3 and CO3 * PCO2 is changing so pH can vary * can also change in microclimates like soil pores * pH of rain water that is at equil with the air is pH = 5.66
    40
    Acid Rain
    * ph 2 -4.5 * due to H2SO4 from SO2 due to coal * S2- + O2 (heat)= SO2 from coal combustion * HNO3 from NOX * N2 + O2 (heat) = 2NO hot temp w/air as fuel
    41
    Time of day impact on CO2
    * pH can range from 5-10 * noon - high photosynthesis which consumes CO2 so highest pH * midnight - respiration produces * At pH 10 then -OH is major factor
    42
    Sand
    SiO2
    43
    CO2 and CaCO3
    * CaCO3 is important for seashells * 1014 is driver for more soluble species than otherwise predicted * CO2 + CaCO3 + H2O = Ca2+ + 2HCO3 - * Ksum = KHKa1KspKb(1/Kw) = 1.5 e 10-6 * Ksum = [Ca2+][HCO3-]2 / PCO2 * Increase CO2 then increase Ca2+ (dissolved shells) * HCO3- is a base species, higher pH than water at equil.
    44
    CaCO3 Solubility
    * Ksum = [Ca2+][HCO3-]2 / PCO2 * Ksum = 4S3 / PCO2 * 390 ppm CO2 parts per million by volume * 390e10-6 atm CO2 per 1 atm total gas * stable ph because more HCO3- so well buffered * Limestone increases pH and is more stable pH
    45
    Alkalinity
    * measures the capacity of a water body to neutralize acid * alkalinity = proton acceptors - proton donors * alkalinity = [OH] + [HCO3] +2[CO3] - H3O * Acid neutralizing capacity is similar * allows for other species of proton donors and acceptors * natural organic matter (NOM), silicates, phosphates, Al3+ * Alkalinity of natural water ranges from 50 - 2000 uM
    46
    Measure Alkalinity
    * carbonate alkalinity * H + CO3 + OH = HCO3 + H2O * phenolphthalein as indicator pH 8.3 * moles of H required to reach endpoint * Total alkalinity * H + HCO3 + CO3 + OH = H2CO3 + H2O * bromocresol green indicator pH 4.5 * moles of H required to reach endpoint * Alkalinity is a capacity factor while pH is an intensity factor
    47
    Alkalinity Uses
    * quantify conc of carbonate ligands available for metal speciation * predict susceptibility of water body to acidification * \<200uM high sensitivity * 200-400 uM moderate sensitivity * \>400 uM low sensitivity * Concrete in urban areas can be source of artificial limestone. Increase alkalinity
    48
    natural organic matter (NOM)
    * product of bio activity (not synthetic) * has acid/base properties * can complex metals * DOM or POM (particulate organic matter) * Discreet small molecules (sugars, small acids, amino acids) or macromolecules (high MW, bio polymers)
    49
    Macromolecules
    * high MW, derived from biological polymers * cellulose: polysaccharides * lignin: aromatic polymer, diverse competition of alcohols * coumaryl alcohol * coniferyl alcohol * sinapyl alcohol
    50
    DOM vs POM
    operational definition use 0.45um filter goes through it is dissolved. stuck in the filter than precipitate Not always true: nanoparticle 100nm will go through filter
    51
    Humic Substances
    * operationally defined based on empirical properties * result from microbial and or abiotic degradation of biopolymers like lignin * represents fragments that are resistant to degradation * oxidation and hydrolysis of biopolymers and polymerization of small organic fragments
    52
    Plant material degradation
    plant material humin - insoluble at all pHs humic acid - insoluble

    fulvic acid - suluble at all pHs

    small molecules
    53
    humic structures
    * humin - very large, few functional groups * humic acid - more oxidized groups, smaller overall, -COOH, -OH. 35% O by mass * fulvic acid - even smaller group, greater proportion of functional groups. 45% O by mass * As humics age, propertied change and higher % O. More oxidized. Greater water solubility. More fulvic acid
    54
    Characterizing humic substances
    * determine average properties * Spectroscopy - IR and NMR to find relative abundance of functional groups * use titrations to find average pka * COOH 2.5-5 * phenols 9-10 * Quantify Kf with metals * DOM contains -COOH, -OH, -N: , -SH * Kf changes with DOM location
    55
    Metal Biogeochemistry
    * pathways and cycles through which metals interact with soild, sediments, and biota * metal toxicity - major elements (Ca, Na, K, Mg) in high conc (essential nutrients) * trace elements - low conc, micronutrients at low levels, tox at higher levels
    56
    Classification of Metals and Ligands
    * Type A, hard metals: low polarizability, prefer O- and N- containing ligands * top left * Type B, soft metals: polarizable, prefer S-containing and heavy halogen ligands. Subject to alkylation (bind to C) * Cd, Zn, Hg
    57
    Aquo Complexes
    M(H2O)62+ Some complexes are ionizable M(H2O)62+ = M(H2O)5(OH)+ + H+ Metal can withdraw electron density from oxygen and reduce the strength of the OH bond -more significant on cations with larger charges Fe2+ pKa = 10.1 Fe3+ pKa = 2.19 * metal salt solutions can be significantly acidic
    58
    Metal Complexes with Humics
    * functional groups on humic material can complex metals * can be multidentate ligands - more than one functional group on the same molecule binds to a single metal ion * factors * metal ion * pH - functional groups ionized or not (are H ion competing with the metal ion for the binding site) * ionic strength - activity * competing ions - other cation in solution? * location, source, age of DOM
    59
    Conditional Stability Constants
    * Kf' * only valid for a set of conditions (pH, ionic strength, competing ions, DOM source)
    60
    Binding Capacity of DOM
    * analogous to concentration of ligand * DOM is heterogeneous so cant determine molar conc * can determine moles of binding sites per L * found via titration * capacity rivers
  • due to age effects
    •
    61
    62
    DOC vs DOM
    * DOC - represents concentration based on mass of C (mg C/L) * measured instrumentally by combustion analysis * CO2 measured by IR detector * approximately 60% of DOM is C * DOM = 1.67\*DOM * DOM measured by high temp oxidation \>450C. Lost mass is presumed to be DOM (volatile solids) * must ensure that sample is totally dry * more time consuming than combustion analysis of C

    Environmental Chemistry (3 decks)

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