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study guide - ENVS 4101 Exam 1 Key Concepts Layering Lake...

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ENVS 4101 Exam 1 Key Concepts:: Layering: Lake Stratification (Layering) and Turnover. Heat from the sun and changing seasons cause water in large lakes to stratify or form layers. In winter, the ice cover stays at 0°C (32°F) and the water remains warmer below the ice than in the air above. Water is most dense at 4°C (39°F). In the spring turnover, warmer water rises as the surface heats up. In fall, surface waters cool, become denser and descend as heat is lost from the surface. In summer, stratification is caused by a warming of surface waters, which form a distinct layer called the epilimnion. This is separated from the cooler and denser waters of the hypolimnion by the thermocline, a layer of rapid temperature transition. Turnover distributes oxygen annually throughout most of the lakes. Acidity: Alkalinity: Speciation: Chelating Agents :
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- Organic chemicals that bond with and remove free metal ions from solution - Often polydentate ligands - Have diverse industrial applications - Conventional chelators are EDTA, NTA - EDTA - most widely used chelator worldwide Ligand : Ligands found in natural and waste waters contain a variety of functional groups including the following: Bonds within metal complexes: a. Determine behavior and stability b. Result from electron pairs donated to the central metal atom by ligands Metal complexes are important in many biological processes. a. Hemoglobin (Fe at its center) b. Chlorophyll (Mg at its center) Other examples of chelating agents: a. Naturally occurring: humic substances, amino acids b. Synthetic chelating agents which enter aquatic systems through waste discharges: i. NTA sodium nitrilotriacetate ii. EDTA sodium ethylenediaminetetraacetate iii. sodium citrate
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iv. sodium tripolyphosphate EDTA: - Cheap to produce, extensively used - Not readily biodegradable - Several countries have enacted regulations restricting its use and discharge. Others have even banned EDTA usage for some applications. - Regulations plus increased environmental levels have sparked concern about toxicity and research into alternative chelators. EDTA is a polyamino carboxylic acid with the formula [CH2N(CH2CO2H)2]2. -Generally, the more biodegradable a chelator is, the less effective it is. -Recently, research has defined alternative chelators that are as effective as conventional chelators, but more biodegradable. -For EDTA, that alternative was [S, S]-Ethylenediaminedisuccinic acid (EDDS.) EDDS: - First synthesized in 1964 by Kezerian et al. - 4 stereoisomers possible: [S, S], [R, R], and [R, S/S, R] - Hexadentate ligand, structural isomer of EDTA - Chemically quite similar - [S, S]-EDDS and its complexonates are easily degraded by photolysis and are ecologically safe. - Various processes for the synthesis of EDDS have been reported since 1964.
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study guide - ENVS 4101 Exam 1 Key Concepts Layering Lake...

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