In water, the ions Ca²⁺ and Mg²⁺ coexist. determine the calcium title by precipitating Mg²⁺ ions in form of Mg(OH)₂ with strong base like KOH 1M or NaOH 1M. To prevent Mg²⁺ to be complexed with EDTA ,first of all adjust the pH of  solution to the PH10 because from 10.4 all Mg²⁺ ions are precipitated in the form of Mg(OH)₂ and titrate the Ca²⁺ ions in the solution by using EDTA

Apparatus and Reagents

·         Conical flask

·         Beaker

·         Sodium hydroxide solution

·         Indicator solution

·         EDTA solution

Procedure:

·         Take 100ml of water sample

·         Add 1ml of NaOH 1M to raise the pH to 12-13

·         Add 1-2 drops of indicator solution,

·         Titrate with EDTA 0.01M until solution changes from pink to purple .and note the volume adjustment

·     Calculation: TCa{[V(EDTA)*M*100]/V_sample}*100

 By knowing that TH=T_Mg +T_Ca; the T_Mg= TH-T_Ca, and the result obtained by this equation is in mg/l of MgCO₃

Finally, the amount of calcium and magnesium can be obtained from the below equations

Ca= T_Ca x 0.4 While Mg=T_Mg x 0.24

References

1        Sadhana C.; Ananda Dev G.; Handbook of Water, Air and Soil Analysis; a Lab Manual; International-E-Publication;2014

2        Frank R.Spellman; Handbook of water and wastewater treatment plant operations; Lewis publishers;2003

3        Leena Deshpande;Water Quality Analysis Laboratory methods; New Delhi; India.