Water Chemistry: Chloride Content

Chloride Occurrence in Natural Waters

• Chloride occurs in all natural waters with varying concentrations.
• The chloride content increases with the mineral content.
• Upland and mountain supplies generally have low chloride levels.
• River and ground-waters typically have a considerable amount of chlorides.
• Sea and ocean waters have very high chloride levels due to partial evaporation of natural waters.

Measurement of Chloride

• Chloride levels can be measured using volumetric procedures with internal indicators.
• Mohr's method is commonly used, employing silver nitrate as the titrant and potassium chromate as the indicator.
• The titration reaction involves the precipitation of chloride ions as white silver chloride.

Titration Endpoint Detection

• The endpoint of the titration cannot be detected by eye without an indicator.
• Potassium chromate is used as the indicator, which forms a reddish-brown precipitate or red color of silver chromate.

Effects of Chloride on Human Health

• Chloride concentrations below 250 mg/L are not harmful to humans.
• Concentrations above 250 mg/L give a salty taste to water, which is objectionable to many people.
• The I.S. Public Health Service recommends limiting chlorides to 250 mg/L in public water supplies.

Chloride in Natural Waters

• Chloride occurs in all natural waters, but its concentration varies widely.
• The chloride content tends to increase as the mineral content increases.
• Upland and mountain water supplies usually have low chloride levels.
• River and groundwater supplies typically have a considerable amount of chlorides.
• Sea and ocean waters have very high chloride levels due to partial evaporation of natural waters flowing into them.

Measurement of Chlorides

• Chlorides can be measured using volumetric procedures with internal indicators.
• Mohr's method is a satisfactory method, which uses silver nitrate as the titrant and potassium chromate as the indicator.
• The titration process involves the precipitation of chloride ions as white silver chloride.

Detection of End Point

• The end point of the titration cannot be detected by eye without an indicator.
• Potassium chromate is used as the indicator, which forms a reddish-brown precipitate or red color of silver chromate.

Health Effects of Chlorides

• Chlorides are not harmful to humans at reasonable concentrations.
• Concentrations above 250 mg/l give a salty taste to water, which is objectionable to many people.
• The I.S. Public Health Service recommends limiting chlorides to 250 mg/l in public water supplies.