Introduction: Chlorides are widely distributed in nature as salts of sodium (NaCl), potassium (KCl), and calcium (CaCl2). These salts of Chlorides are widely used in the production of different industrial chemicals such as Sodium Chloride is used for the production of caustic soda, chlorine, sodium chlorite, and sodium hypochlorite. These salts are extensively used in snow and ice control. Potassium chloride is used in the production of fertilizers (WHO, 1996).
Sources of Chloride in Environment:
Natural: Usually Chlorides are leached from various rocks into soil and water due to weathering. The ions of chloride are highly mobile and are transported to closed basins or ocean. Chloride occurs naturally in foodstuffs at levels normally less than 0.36 mg/g. (WHO, 1996)
Anthropogenic: Chloride in water may be considerably increased by treatment processes, used for the purification of water, in which chlorine or chloride is used. Addition of salt in food during processing, cooking, or eating can markedly increase the chloride level in food (WHO, 1996).
Chloride ions in a water sample can be determined by Argentometric method.
Principle: This method is based on the precipitation and titration in which from the burette silver nitrate solution is released to the chloride ions and indicator containing water sample. The silver ions will react with chloride ions and the chromate ions to form white precipitate of silver chloride and red precipitate of silver chromate.
Ag+ + Cl– AgCl (white precipitate)
2Ag+ + CrO42- Ag2CrO4 + CrO42- (red precipitate)
Procedure:
Titration with the Blank solution: Take 25 ml of the distilled water in a conical flask and add 3-4 drops of potassium chromate solution. Slowly add standard silver nitrate solution from the burette and shake the solution well. At the end point, light yellow colour starts changing to red colour. The titration is repeated until a concordant volume V1 is obtained.
Titration with the Sample Water: Take 25 ml of the given water sample in a conical flask and add 3-4 drops of potassium chromate solution. Slowly add standard silver nitrate solution from the burette and shake the solution well. At the end point, light yellow color starts changing to red colour and red colour persists. The titration is repeated until a concordant volume V2 is obtained.
Observations and Calculations:
Titration with the Blank solution
| Sr. No. | Volume of distilled water in ml | Volume of AgNO3 solution in ml | |
| 1 | 25 | 0.1 | |
| 2 | 25 | 0.2 | |
| 3 | 25 | 0.2 |
Concordant Volume of AgNO3 solution, V1 = 0.17 ml
Titration with the Sample Water
| Sr. No. | Volume of distilled water in ml | Burette Readings in ml | Volume of AgNO3 solution in ml | |
| Initial | Final | |||
| 1 | 25 | 0 | 7.5 | 7.5 |
| 2 | 25 | 7.5 | 14.8 | 7.3 |
| 3 | 25 | 14.8 | 22.4 | 7.6 |
Concordant Volume of AgNO3 solution, V2 = 7.46 ml
Calculations:
Volume of titrant used = V2-V1
= 7.46-0.17 ml = 7.26 ml
Volume of given water sample, VW = 25
Molarity of given water sample, MW = MA X VA
VW
= 0.01 x 7.26N = 0.002904
25
Amount of chloride ions = MW x 35.45 x 1000 mg/Lit
= 0.002904 x 35.45x 1000 mg/Lit
= 102.94 mg/l
Result:
The amount of chloride ion in the given water sample is 102.94 ppm
Environmental Impacts of Chloride ions:
Human Health Impacts:
Diseases associated with chloride intake are rare. Chloride toxicity can be expected only in those who have impaired NaCl metabolism. Due to deficiency of chloride alkalosis and Hypochlorem can occur its symptoms include loss of appetite, lethargy, and muscle weakness heavy sweating (Brazin, 2006)
Plants impacts
Cl— free media results in substantial reduction of growth of many plants. Cl— deficiency causes reduced leaf growth and wilting, followed by chlorosis, bronzing and, finally, necrosis. Roots become stunted and the development of laterals is suppressed. Fruits are decreased in numbers and size (WHITE & BROADLEY, 2001).
Different Standards for Chlorides in Different Mediums:
| Category | Max. limit | Standardizing Agency |
| Drinking Water | 200 mg/l | WHO (1996) |
| Drinking Water | 250 mg/l | EPA |
| Aquatic plants | 200 – 36,400 mg/l | USEPA (1998) |
| Waste Water | 500 mg/l | NEQS (1999) |
References
- Brazin, J. (2006). Chloride & Its Consequences .
- White, P. J., & Broadley, M. R. (2001). Chloride in Soils and its Uptake and Movement within the Plant: A Review. Annals of Botany, 967-988.
- (1996). Guidelines for drinking-water quality. Geneva.
See related links also:
Determine the Amount of Sodium in water and soil