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.
• 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 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
Hydrostatic Balance
Salt water intrusion
Hydrostatic Balance
Salt water intrusion
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
of surface water.
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
• 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.
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.
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
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
Instrumental Methods
• Automated ferricyanide methodColorimetric
• Ion chromatography
Mohr Method
0.0141 N silver nitrate ( N / 71 )
Each ml = 0.5 mg ClCl- 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 Method
1. Sample size 100 ml
2. pH 7-8 Ag+ ppt as AgOH at high pH levels and
CrO-24 is converted to CrO-27 at low pH.
3. A definite amount of indicator
Cl- (mg/L) = ( ml AgNO3 – blank)*0.5 *1000
ml sample
0.0141 * 35.45 =0.5
Mercuric Nitrate Method  Reading assignment