Environmental Chemistry Guide

Environmental Chemistry: Assessment Statement Test This test will cover Option E in the IB Chemistry guidelines, except for a few areas of soil that still confuse even Mrs. Nagel. The following outline sums them up!

DEFINITIONS! 1. Acid Deposition – Any combination of dry/airborne acidic particles, or precipitation, that falls to earth. Acidic here means rain pH<5.65. Natural rain is slightly acidic because of presence of CO2, which combines with H20: CO2 + H2O -> H2CO3 2. DO – Dissolved oxygen in water. It’s an important sign of microorganic life in water, as well as an indicator of purity and ability to sustain life. 3. BOD – Biochemical Oxygen Demand. Measure of quantity of oxygen consumed by microorganisms during decomposition of organic matter. High BOD = Low DO 4. Eutrophication – Cycle of consumption of free phosphates/nitrates in water, leading to plant growth and death, leading to release of more phosphates/nitrates by decomposing bacteria. Is only bad when it cycles too rapidly, leading to overpopulation of plant growth, low DO, and choked lake. 5. Aerobic decay – O2 used to break down organic matter.

Results in: C -> CO2 N -> NO3S -> SO4-2 P -> PO4-3 6. Anaerobic decay – Organic matter decomposed oxygen-free!

Results in: C -> CH4 (methane)

N -> NH3 and amines S -> H2S P -> PH3 (phosphine) 7. Distillation – Process by which water is heated in coiled pipes, forced to evaporate, and continues heating; all in order to prepare salt water for drinking. 8. Reverse osmosis – Process by which, using high pressure, water is forced through a semi-permeable membrane in order to remove unwanted material so that the water is drinkable. 9. Humus – Mixture of simple and complex organic chemicals of plant, animal, or microbial origin. Basically, nonliving organic matter. 10. Salinization – Accumulation of salts in soil—caused by excess irrigation and poor drainage Can lead to toxic buildups of salt, or dehydration. 11. Nutrient depletion – Over-intense absorption of nutrients—caused by constant farming of the same old plants Can lead to total nutrient depletionuseless soil 12. Soil pollution – Presence of harmful materials in soil—caused by industrial waste, oil, and pesticides Can reduce biodiversity and ruin soil 13. SOM – Soil Organic Matter. Organic constituents (plant or animal tissues/partially decomposed products/soil biomass) of soil Composed of organic matter broken into a mixture of smaller molecules SOM can be found by titration with dichromate solutions. 14. Mineralization – Breaking down of organic matter to get nitrogen/phosphates into the roots of plants.

It ALWAYS comes back to N and P. Importance: Biological – Creates reservoir of nutrients (N, S, and P) Physical – Soil clusters collect in stable form to reduce erosion and hold water Chemical – Increases CEC (below); acts as pH buffer; chelation

CHELATION – Formation of complex ions from metals; removes metals from use in soil. Can be good or bad depending on the metals. 15. CEC – Cation Exchange Capacity. Extent to which negative charges in humus and clay can be traded with nutrient cations at roots of plants. (ie. Amount of cations a soil can hold) Indication of soil’s fertility Enhances ability of soil to be a pH buffer Removes toxins.

FORMULAS! Sulfuric acid comes from: Combustion. S + O2  SO2 + H2O  H2SO3 Or SO2 + ½O2  SO3 + H2O  H2SO4 Nitric Acid comes from: Internal combustion. N2 + O2  2NO Or N2 + 2O2  2NO2 NO2 + H2O  HNO3 + HNO Precipitation of Calcium by Sulfate ions: Ca+2 (aq) + SO4-2 (aq)  CaSO4 (s)

METHODS/EXPLANATIONS! Acid Deposition: Sources N – Internal Combustion Engines Bacterial decomposition Electrical storms S – Volcanoes Combustion of fossil fuels Ore-smelting

Acid Deposition: Removal/Reduction N and S – Improved Engine Design Catalytic converters Liming (neutralizes acidity) S – Coal-washing Stack scrubbers Reduce amount burned N – Alternative engine fuels ALSO INVOLVED IN ACID DEPOSITION: AMMONIA NH4+ (aq) + 2O2 (g)  2H+ (aq) + NO3- (aq) + H2O (l) Ammonia comes from rhizobia bacteria in soil, legumes, etc. It can neutralize acids from rain to reduce their effect. Yay!

SOIL pH: GOOD PH MEANS 6-7.5. Anything else is bad. THREE FACTORS AFFECTING DO in water: 1. Thermal pollution/Temperature High temp = Low DO 2. Eutrophication Too much anaerobic decay/overpopulation of organisms = Low DO 3. Presence of Organic Waste Too much waste = Low DO

In general, High BOD (caused by presence of aerobic, respirating organisms) means LOW DO. Finally, sewage treatment. • Important because it allows water to be recycled by removing unwanted waste. • Primary treatment: Simple filters remove large waste. • Secondary: trickle filters or aerobic bacteria remove water that is bubbled with oxygen, allowing natural decomposition of waste. • Water is disinfected with Cl or Ozone. • Tertiary treatment: Removes N and P from water. More expensive, but necessary. Precipitation is used to remove metals. C’est tout (that’s it) for the guide tonight! Refer to pages 132, 135-138, 142, and 143 for more information. Good luck!