PRINCIPLE OF HARDNESS DETERMINATION Hardness determine by EDTA method. In this method Erichrome Black T (EBT) indicator and Ethylene Diamine Tetractic Acid ( EDTA) as an titrant. EBT when added in hard water it react with Ca ++ & Mg ++ & other divalent hardness producing ions to form weak wine red color complex. At higher pH, this weak wine red color complex combines with EDTA (titrant) to form a stable blue color Complex. Chemicals: 1) Hardness Buffer ( to maintain a pH of10) 2) Erichrome Black T -indicator 3) EDTA(Titrant) PROCEDURE: Part A: Sample Titration: a) Take sample in conical flask 25ml. b) Add 100ml of distilled water and 1 to 2 ml hardness buffer solution to maintain pH 10. (as weak complex and stable complex formed at high pH). c)Add EBT indicator in conical flask and mix to form wine red color. d) Titrate with EDTA. (Add titrant drop by drop till stable sky blue color is formed) e) Record amount of EDTA titrant used for sample titration. Part B: Blank Correction: Repeat step b to e of part A. Part C: Standardization of EDTA Titrant: a) Take 10ml of 0.02N standard ZnSO 4 solution. b) Add 100ml of distilled water and 1 to 2 ml hardness buffer solution to maintain pH 10. c) Add EBT indicator in conical flask and mix to form wine red color. d) Titrate with EDTA. (Add titrant drop by drop till stable sky blue color is formed). e) Record amount of EDTA titrant used for sample titration. CALCULATION OF TOTAL HARDNESS: Total hardness = ((X – Y) x Normality of Titrant x 50 x 1000) / Volume of sample (25 ml) X = Volume of titrant used for sample titration (Part A) Y = Volume of titrant used for sample titration (Part B) 50 in formula = Equivalent weight of CaCO 3 1000 in formula it is to convert ml to liter. POST NAVIGATION