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DO 和 COD

DO 和 COD. 时间安排. 预习时，洗净玻璃器皿，将溶解氧瓶带回宿舍，每人 1 瓶。 星期四上午 8:10 ，在“若谷”学区前的湖边，采集湖水样品，每人 1 瓶。此外，每组再多采集 1 个矿泉水瓶的湖水样品。 回到实验室，集中听讲解。 分头做实验，上午 DO ，下午 COD 。 要穿实验服。. 2.7. Determination of Dissolved Oxygen.

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DO 和 COD

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  1. DO 和 COD

  2. 时间安排 • 预习时，洗净玻璃器皿，将溶解氧瓶带回宿舍，每人1瓶。 • 星期四上午 8:10，在“若谷”学区前的湖边，采集湖水样品，每人1瓶。此外，每组再多采集1个矿泉水瓶的湖水样品。 • 回到实验室，集中听讲解。 • 分头做实验，上午DO，下午COD。 • 要穿实验服。

  3. 2.7. Determination of Dissolved Oxygen • Purpose: To understand the principle of determination of dissolved oxygen, and to master one of the volumetric methods, redox titration, as well as the sample collection and storage for the analysis of dissolved oxygen.

  4. Questions • What is DO? • What are the factors affecting the concentration of DO? • Salinity, temperature, algae, air pressure • What carefulness/attention should be taken when sampling DO sample? • Any contact with air or agitation should be avoided, and no air bobbles are allowed.

  5. Redox titration H+ O2 Mn(II) Mn(OH)4 dis. Mn(IV) MnO(OH)2 (MnO2.2H2O) Mn2+ + I2 S2O32- I- + S4O62- I-

  6. Indicator: starch solution I2 + starch blue I- + starch colorless

  7. Additional questions • Describe the compound formation color change during the titration. How does the color change?

  8. Sample handling • One sample, two titrations for each student. • Carefully with H2SO4

  9. 2.8. Determination of Chemical Oxygen Demand (COD) • Purpose: To understand the definition of chemical oxygen demand and the principle of its determination, and to master one of the volumetric methods, redox titration, as well as one of the sample pretreatment methods, digestion.

  10. Definition of COD, BOD, TOC Note: • Under definite conditions • Relative index Catalyst: Ag2SO4 Type of titration: back redox titration

  11. Back titration Known titrant Fixed K2Cr2O7 COD? Vb＞Vs for titrant For blank, COD～0, Vb very high

  12. bio-degradable organic ～BOD ～TOC non-biodegradable Pollutants COD oxidizable inorganic reducible TOC＞COD＞BOD

  13. Procedure • Digestion, using K2Cr2O7 or KMnO4 Fast digestion, with digesting tube and heater (hot!) 2. Titration, using redox method Indicator: Ferroin (phenanthroline ferrous sulfate) Titrant: Ferrous ammonium sulfate

  14. Sample handling 1 blank + 1 sample for each student If there is only one digesting tube, do the blank first. 3 mL sample + 5 mL digesting solution

  15. Questions • Which of the following reagent should be measured exactly? K2Cr2O7, Ag2SO4/H2SO4, sample

  16. Attention! • Be careful with the hot plate! • Put the label on!

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