Water Analysis : To Estimate The Total Hardness Of Water

INTRODUCTION:

Hardness is define as the concentration of multivalent cationas in solution originally, water hardness as understood to be a measure of the capacity of precipitate soap. Soap is chiefly precipitate by calcium & magnesium ion present in water

Other polyvalent cations also may get precipitate. So, they often are in complex form frequently with organic constituents and have a role in water hardness. Total hardness    is defined as sum of calcium & magnesium concentration. Both are expressed as calcium carbonate in/l.

When hardness is numerically greater then the sum of carbonate and bi-carbonate alkalinity, that amount of hardness equivalent to total alkalinity   is called carbonate hardness. The amount hardness in exams of these is called non-carbonate hardness. When the hardness remain in the range of 100, 200, 300… mg/l   depending on the lower 7 treatment to which water has been subjected

According to international standard ISO (10500:1991), hardness of drinking water=< 300 mg/l to 600 mg/l

Hardness Range (mg/l  as CaCO3)	Degree of Hardness
0-75	Soft
75-150	Hoderatory hard
150-300	Hard
7300	Very hard

Reactions:

Ca(HCO₃)₂ + Heat   ----------> CaCO₃ (pp+ )+CO₂+H₂O

Mg(HCO₃)₂+Heat ------------> MgCO₃ (pp+  )+CO₂+H₂O

 

AIM: ESTIMATION OF TOTAL HARDNESS

PRINCIPLE:

In alkaline condition, EDTA or its sodium salt reacts with calcium & magnesium to form soluble chelate complex. Ca & Mg ions develop wine red color small amount of dye (Erichrome Black T) EBT is added under alkaline condition. When EDTA is added as a titrate, the Ca & Mg will be complexed with EDTA resulting in pharp change from wine red to blue which indicates end-point of titration.

M+2 + EBT --------> M – EBT Complex

M - EBT + EDTA ---> M –EDTA Complex + EBT (blue color)

Where, M = Ca & Mg

REQUIREMENT:

•        Buffer Solution

-          NH₄Cl 16.9 gm

-          Con. NH₄OH 143 ml

-          EDTA  1.179 gm

-          MgSO4  0.78 gm

-          D/W (final volume)  250 ml

•        Erichrome Black T Dye

-          0.095 gm dye  + 10 gm NaCl

•         Std. EDTA solution (0.01 M)

-          EDTA 3.723 gm

-          D/W 1000 ml

PROCEDURE:

-          Dilute 25 ml sample to about 50 ml with D/W

-          Add 1 or 2 ml of buffer solution usually 1 ml will be sufficient to give the PH around 10.0

-          Add a pinch of EBT and titrate with std. EDTA solution till wine red color changes to blue. Note down the volume of EDTA consumed (A).

-          Run a reagent blank as with D/W as per above method.

-          Note down the amount of EDTA (B).

-          Calculate the volume of EDTA requirement by sample

CALCULATION:

Hardness as MgCaCO₃/l =  ( C * X *1000) / ml of Sample

Where, c = ml of titration (EDTA)

              X = MgCaCO3 equivalent to ml EDTA titration = 1 ml