The Islamic University of Gaza- Environmental Engineering Department Environmental Measurements (EENV 4244) Lecture 6: Anions Chloride and Nitrate Prepared by Husam Al-Najar

Chloride concentration in groundwater Chloride concentration Map 2007 Chloride concentration Map 2002

Chloride concentration Map 2020

Chloride: Argentometric titration Principle In neutral or slight alkaline solution, potassium chromate (K2CrO4) can indicate the endpoint of AgNO3 titration of chloride AgCl is precipitated quantitatively before red Ag2CrO4 is formed. Interference Substances in amounts normally found in potable waters will not interfere Br, I and CN register as equivalent Cl. Sulfide, S2O3 and SO3 interfere but can be removed by treatment with H2O2 . Orth-PO4 in excess of 25 mg/l interferes by precipitating as Ag3PO4 Fe in excess of 10 mg/l interferes by masking the end point Apotentiometeric method is suitable for colored or turbid samples in which the color indicated endpoint might be difficult to observe. However, a turbidity and color can also be removed by treatment with Al(OH)3.

2. NO3-., U.V Spectrophotometer screening method Principle Use this method only for screening samples that have low organic matter contents; i.e. uncontaminated natural water and potable water supply. Measurements of UV absorption at 220 nm enables rapid determination of nitrate. Because dissolved organic matter also may absorb at 220 nm and NO3 does not absorb at 275 nm, a second measurement made at 275 nm may be used to correct the NO3 value. The extend of this empirical correction is related to the nature and concentration of organic matter and may vary from one water to another. Acidification with I M HCl prevents interference from hydroxide or carbonate concentration up to 1000 mg CaCO3/l. Interference Dissolved organic matter, surfactants, NO2-, Cr6+, chlorite and chlorate interfere. Chloride has no effect on the determination.