December 01,2016 11:00 pm
Chlorides are widely distributed in nature as salts of sodium (NaCl), potassium (KCl), and calcium (CaCl2).
Principle
In this experiment, the given water sample in presence of potassium chromate indicator is titrated against silver nitrate solution (AgNO3). The silver nitrate reacts with chloride test present in the sample resulting in the formation of silver chloride. The end point of titration is indicated by formation of red silver chromate from excess silver nitrate.
Range
| Drinking Water Standards of BIS (IS: 10500: 1991) | ||
| Parameter | Desirable limits mg/L | Permissible limits mg/L |
| Chloride (Cl) | 250 | 1000 |
| Effects of water quality parameters of water being used in industries | |||
| Parameter | Prescribed limits IS:10500, 1991 | Probable effects | |
| Desirable limit | Permissible limit | ||
| Chloride mg/l | 25 | 200 | Significantly effect the rate of corrosion of steel and Aluminum. |
Analysis Procedure : [IS 3025-32 (1988)]
Used I00 ml samples.
added 3 ml of aluminium hydroxide suspensions, mixed, let settle and filters.
Sulphite or thiosulphate are presents, added 1 ml of hydrogen peroxide and stire for I minute.
Adjustable samples pH to 7-10 with sulphuric acid or sodium hydroxide if it's not in the range.
Added 1.0 ml of potassium chromate indicator solutions.
Titrate with standard silver nitrate solution to a pinkish yellow end point.
Calculations
Precautions
Silver Nitrate (AgNO3) should be stored safely in brown colored bottle to prevent exposure to sunlight.
Silver nitrate should be handled carefully to avoid any spillage. It can result in scar on the skin.
Interference
Bromide, iodide and cyanide register equivalent chloride concentrations. Sulphite, thiosulphate and sulphide ions interfere but can be removed by treatment with hydrogen peroxide. Orthophosphates in excess of 25 mg/l interfere by masking the end point. Iron in interferes by masking the end point.
Applications
In many areas the level of chlorides in natural waters is an important consideration in the selection of supplies for human use.
It is an important parameter in wastewater as high chloride content may harm metallic pipes and structures as well as growing plants.
Where brackish waters must be used for domestic purposes, the amount of chlorides present is an important factor in determining the type of desalting apparatus to be used.
Chloride determination is used to control pumping of ground-water from locations where intrusion of seawater is a problem.
Sodium chloride has a considerable history as a tracer. One of its principal applications has been in tracing pollution of wells.
Conclusion
Chloride is one of the major inorganic anion in water and wastewater. In potable water, the salty taste produced by chloride concentrations is variable and dependent on the chemical composition. Chloride concentration is higher in wastewater than in raw water.
Disclaimer
The details given are for general understanding. References should be taken from respective authorized agencies.