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ENVE 201 Environmental Engineering Chemistry 1

ENVE 201 Environmental Engineering Chemistry 1. CHLORIDES (Chapter 21) Dr. Aslıhan Kerç. Chlorides. As mineral content ↗ Cl - ↗ Upland, Mountain supplies low in Cl - High in rivers and groundwater Sea-Ocean ↗. Sources of Chloride. Surface waters dissolve chlorides from top soil.

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ENVE 201 Environmental Engineering Chemistry 1

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  1. ENVE 201EnvironmentalEngineeringChemistry 1 CHLORIDES (Chapter 21) Dr. Aslıhan Kerç

  2. Chlorides As mineral content ↗ Cl- ↗ • Upland, Mountain supplies low in Cl- • High in rivers and groundwater • Sea-Ocean ↗

  3. Sources of Chloride • Surface waters dissolve chlorides from top soil. • Spray from the ocean is carried in land as droplets. • Ocean and sea waters invade the rivers that drain into them. • Intermixing between freshwater and saltwater layers

  4. Sources of Chloride There is a hydrostatic balance between seawater and groundwater in areas adjacent to the ocean. Over pumping of groundwater disturbs the balance.  Salt water intrusion into well

  5. Hydrostatic BalanceSalt water intrusion

  6. Hydrostatic BalanceSalt water intrusion

  7. Effect of Evapotranspiration Evapotranspiration of water used for irrigation • Lost to the atmosphere • Leaving the salt in the soil • Destruction of soil’s crop-growing potential Highly saline irrigation water return to the surface waters Normal evaporation also increases salt content ofsurface water.

  8. Chloride in Wastewaters • Human urine contain chloride  originating from consumed food and water 6 gr Cl- / person / day • Cl- in municipal wastewater 15 mg/L  discharge to the surface water • Industrial wastes also contain Cl-

  9. Chloride in Drinking Water • Concentration above 250 mg/L give a salty taste • For public use limit 250 mg/L • In arid regions  2000 mg/L can also be used , human system become adapted.

  10. Before development of bacteriologic test, Cl- and nitrogen determination  used for detecting contamination of groundwater by wastewater Cl- measurement and total salinity  important for irrigation water Chlorides can be used as tracers in Env. Eng.  in groundwater studies.

  11. Methods of Determination • Mohr method (Argentometric)  Employing silver nitrate as the titrant Potassium chromate as the indicator • Mercuric nitrate method Mercuric nitrate  titrant Diphenylcarbazone  indicator

  12. Instrumental Methods • Potentiometric titration  change in the potential between a reference electrode and silver-silver chloride electrode Titration w/silver nitrate solution Chloride present complexes with silver ions When all chloride complexes  silver ion concentration increases Sudden increase in voltage

  13. Instrumental Methods • Automated ferricyanide methodColorimetric • Ion chromatography

  14. Mohr Method 0.0141 N silver nitrate ( N / 71 ) Each ml = 0.5 mg Cl- Cl- is precipated as silver chloride Ag+ + Cl-  AgCl (white precipitate) End point  presence of excess Ag+ 2 Ag+ + CrO-24 Ag2CrO4 (reddish-brown ppt)

  15. Mohr Method • Sample size 100 ml • pH 7-8 Ag+ppt as AgOH at highpHlevelsandCrO-24 is convertedtoCrO-27 at lowpH. • A definiteamount of indicator Cl- (mg/L) = ( ml AgNO3 – blank)*0.5 *1000 ml sample 0.0141 * 35.45 =0.5

  16. Mercuric Nitrate Method  Reading assignment

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