lect 6 Flashcards
what is the overview of intermolecular forces?
-dispersion forces are the weakest of the IMF (< 5 kJ/mol)
-dispersion forces are present in all molecules and atoms
-the magnitude of the dispersion forces increases with molar mass
-polar molecules also have dipole-dipole attractive forces (25 kJ/mol)
-ion-dipole attractions are the strongest intermolecular attraction (100-300 kJ/mol)
what is in chapter 3?
-water and properties
-aquatic chemistry- gases, water, pH and alkalinity, solution equilibria, Ca and other other metals
-complexation equilibria- metals, ligands, and effects of complexation on solution equilibria
what are the important properties of water?
-forms hydrogen bonds with itself and other compounds in solution
-it is a polar molecule
-unusual thermal properties
what is the important property of water of it forms hydrogen bonds with itself and other compounds in solution?
-higher boiling point than expected
-water expands on freezing, max density at 4 degrees celcius
-large surface tension
what is the important property of water of it being a polar molecule?
-good solvent due to hydration
-high electric constant (80 vs. 1 for air) makes water a good solvent for ionic compounds
what is the important property of water of the unusual thermal properties?
-high heat capacity
-high latent heat of fusion and evaporation (good environmental thermal regulator because it stores alot of heat)
-good thermal conductor (good thermal regulator of organisms)
what is the table of the important properties of water?
what is the graph of the hydrologic cycle with quantities of water in trillions of liters per day?
what is the graph that shows the dipole nature of water?
what is the graph of hydrogen bonding?
what is surface water?
in streams, lakes, estuaries
what are the characteristics of wetlands?
shallow, flooded areas with bottom-rooted plants
what are the characteristics of estuaries?
arms of the oceans into which streams flow
Wetlands and estuaries are particularly important parts of the biosphere
-nurseries for many organisms
-food sources for organisms
what is stratification?
stratification of water water bodies can have important effects on the biology and chemistry that occur in them
what is the structure of bodies of water?
-thermal properties of water lead to stratification of bodies of water (formation of layers)
-upper layer is called epilimnion
-lower layer is called hypolimnion
-the two layers are separated by a thermocline (the two layers do not mix well)
what are the seasonal changes due to temperature in water?
-situation for lakes and other small bodies of water
what are the important chemical processes in water?
what are autotrophic organisms?
producers (photosynthesizers)
-utilize solar or chemical energy
-synthesize complex biochemicals from simple inorganic compounds
-photosynthetic aquatic algae are producers that make biomass from CO2 and other inorganic compounds
what are heterotrophic organisms?
metabolize organic materials
-decomposers (reducers) break down material of biological origin
what is productivity and eutrophication?
-productivity is the ability of organisms in a body of water to produce biomass that is the basis of the food chain
eutrophication caused by excess productivity
-decay of excess biomass
-consumption of oxygen
what are the main physical factors affecting aquatic life?
-temperature
-transparency
-turbulence
oxygen in water
-dissolved oxygen, DO
-biochemical oxygen demand, BOD, from degradable substances
what is the introduction to aquatic chemistry?
common chemical phenomena occur in water
-acid-base
-solubility
-oxidation-reduction
-complexation
-biochemical (oxidation-reduction)
aquatic systems are complicated, open and dynamic
-solid phases
-gas phases
-organisms
simplified models based upon equilibrium conditions (rates of processes, kinetics, also important)
what is the graph of the major aquatic chemical processes?
what is the graph of redox chemistry in water? what does oxic and anoxic mean?
-oxic= in contact with the atmosphere (oxygen rich environment)
-anoxic= reducing conditions (oxygen depleted environment)
what are the gases in water?
-O2 for fish
-CO2 to support algal support
-henry’s law: the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas in contact with the liquid
what is the chemistry of natural water?
dissolved gases and henry’s law
-gases partition between the atmosphere and the water
-governed by the partial pressure of the gas in the atmosphere
-HL: the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas in contact with the liquid
what is the graph of henry’s law?
what is the summary of henry’s law?
what is the graph of some examples of henry’s law constants?
gases are less soluble at ______________
higher temperatures
-because for the process X(g)->X(solv), enthalpy (H) and entropy (S) are negative
-enthalpy decreases as system becomes more stabilized and greater order decreases entropy (e.g. fishing lake trout)
nonpolar compounds (e.g. methane: not very soluble in water)
-entropy is very negative. Water molecules form a cage around CH4, giving a more ordered system
-CH4(g) to CH4 (aq) is exothermic (enthalpy, H, is negative)
example of oxygen in water: Calculate the biomass required to deplete the ambient level of oxygen dissolved in water, where its concentration is 8.32 mg/L O2?
-from air (20.85% O2 on basis of dry air)
-8.32 mg/L O2 in water in equilibrium with air at 25 degrees celcius
-solubility decreases with increasing temperature
-oxygen consumed by biodegradation of biomass: CH2O+O2->CO2+H2O
-8.3mg O2 consumed by only 7.8 mg CH2O
-thus, 7.8 mb biomass will deplete the oxygen in L of water at 25 celcius degrees
example: calculate the solubility of oxygen in water based on the Henry’s law constant at ambient conditions?
why is the concentration of O2 in water important? what feature distinguishes the estimation of the oxygen and carbon dioxide levels and their chemical fate in aqueous medium?
-fish need 5-6 mg/L O2 to survive
-CO2 can interact physically and chemically with water (can undergo hydrolysis when dissolved)
what can affect O2 concentration?
-heat (thermal pollution) can lead to decreased O2 solubility (recall gas solubility versus T)
-decreased O2 conc also due to decomposition of biomass called biological oxygen demand (BOD) and chemical oxygen demand substances (COD)
