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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

ENVE 201EnvironmentalEngineeringChemistry 1

CHLORIDES

(Chapter 21)

Dr. Aslıhan Kerç

chlorides
Chlorides

As mineral content ↗ Cl- ↗

  • Upland, Mountain supplies low in Cl-
  • High in rivers and groundwater
  • Sea-Ocean ↗
sources of chloride
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
sources of chloride1
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

effect of evapotranspiration
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.

chloride in wastewaters
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-
chloride in drinking water
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.
slide11

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.

slide12

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

slide13

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

slide14

Instrumental Methods

  • Automated ferricyanide methodColorimetric
  • Ion chromatography
mohr method
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)

mohr method1
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