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 -> NO3-

S -> SO4-2

P -> PO4-3

6. Anaerobic decay – Organic matter decomposed oxygen-free!Results in:C -> CH4 (methane)

N -> NH3 and aminesS -> H2SP -> 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 depletionuseless 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 soilComposed of organic matter broken into a mixture of smaller

moleculesSOM 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 waterChemical – 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 fertilityEnhances ability of soil to be a pH bufferRemoves 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: SourcesN – Internal Combustion Engines Bacterial decomposition Electrical storms

S – Volcanoes Combustion of fossil fuels Ore-smelting

Acid Deposition: Removal/ReductionN and S – Improved Engine Design

Catalytic convertersLiming (neutralizes acidity)

S – Coal-washingStack scrubbersReduce 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/TemperatureHigh temp = Low DO

2. EutrophicationToo much anaerobic decay/overpopulation of

organisms = Low DO

3. Presence of Organic WasteToo 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!