Determination of Chlorides Concentration in water
1) What is the WHO guideline value for chlorides?
No health-based guideline value is proposed for chloride in drinking-water by W.H.O However, chloride concentrations in excess of about 250 mg/litre can give rise to detectable taste in water. The EPA Secondary Drinking Water Regulations recommend a maximum concentration of 250 mg/1 for chloride ions. The WHO recommended concentration of Cl- ion in potable water is a maximum of 200mg/l. Recommended Guidelines for Chlorides Chlorides limit in use of water
2) What is the significance of chlorides test for construction purposes?
Chloride ions when present in reinforced concrete can cause very severe corrosion of the steel reinforcement. The chloride ions will eventually reach the steel and then accumulate to beyond a certain concentration level. The protective film around the steel is destroyed and corrosion will begin when oxygen and moisture are present in the steel-concrete interface. Chlorides can originate from two main sources as follows: Chloride added to the concrete at the time of mixing, often referred to as Internal Chloride. This category includes calcium chloride accelerators for rapid hardening concrete, salt contaminated aggregates and the use of sea water or other saline contaminated water. chloride ingress into the concrete from the environment often referred to as External Chloride. This category includes both de-icing salt as applied to many highway structures and marine salt, either directly from sea water in structures such as piers, or in the form of air-borne salt spray in structures adjacent to the coast. Principle of Reinforcement Corosion
3) How chlorides gain access to natural waters?
Chloride is one of the major anions to be found in water and sewage. Its presence in large amounts may be due to natural processes such as the passage of water through natural salt formations in the earth or it may be an indication of pollution from sea water intrusion, industrial or domestic waste or deicing operations. The primary source of chloride is halite (salt) and brines. Anthropogenic (human) sources of chloride include fertilizer, road salt, human and animal waste, and industrial applications. These sources can result in significant concentrations of choride in shallow ground water because chloride is readily transported through the soil.
4) What would be the role of mixed indicator in this titration?
Mixed indicator is added in acid-base titration because a mixture of two indicator substances is used to give sharper end-point color change. To make the light color to dark so that we can detect the end point easily. So mixed indicator Diphenyl Carbazone or Xylene Cyanol is added to enhance the color for better indication of the end point to get more accurate results.
5) Why different procedures are used depending upon chlorides concentration?
The chloride content of natural surface waters will depend to a great extent on the geology of the area. In a limestone area like Richmond, the natural surface water has very little chloride in it (10-50 mg/L). Any appreciably higher chloride concentration would suggest contamination. High concentrations of chloride can be damaging to metal pipes and structures, as well as to agricultural crops. Different procedures are used depending upon the chlorides concentration because when chloride ion will react with Hg+2 to form HgCl2 (in concentration of chlorides > 100mg/L) which are white precipitates and are insoluble and will faint the color complex and the end point cannot be indicated properly.
Chlorides in Water