Exam 1 (ch 10, 11, 12, 13) Flashcards
1
Q
Uses for water
A
- drinking
- cleaning
- agriculture
- waste water
- industry cooling
- recreation
- wildlife
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)
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
4
Q
Free Ion Activity Model
A
- free metal is actually M(H20)6 2+
- octahedral
- aquo species
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
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
7
Q
Receiving water
A
any body of water that gets input of material from human activities
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.
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.
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
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)
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
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
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
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
16
Q
Soil solution
A
-centrifuge water out of soil
17
Q
Soil/Water levels
A
- soil surface
- water table (unsaturated)
- groundwater (saturated pores)
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
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
20
Q
Water red and ox
A
oxidation - 6H2O = 4H3O+ + O2 + 4e
reduction - 2H2O + 2e = H2 + 2OH-
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
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
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
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
