SOP For Total Hardness in Water and waste water
EDTA Titrimetric method
Purpose:
The purpose of this protocol is to provide guidelines for analysis of Total Hardness in Water.
Principle of method: EDTA and it's sodium salts from a chelated solution complex when added to a solution of certain metal actions, if a small amount of dye such as Eriochrome Black T is added to an aqoeous solution containing calcium and magnesium ions at a pH of 10+0.1 to 10-0.1, the solution becomes winr red. When titrated with EDTA , the magnesium and calcium will be complexed, and when all of the and has been complexed the solution turns from wine red to Blue.
Instrument/Equipment:
The following items are necessary to perform the analysis of Total Hardness in Water;
pH Meter
Burette – 50 ml capacity
Glass Wares
Reagents/Chemicals:
All the chemicals should be of Analytical Reagent Grade.
Distilled Water
Buffer Solution – Dissolve 16.9 g of Ammonium Chloride (NH4Cl) in 143 ml Ammonia and dilute to 250 ml.
Eriochrome Black T indicator solution – Mixed 0.5g dye with 100g NaCl.
Inhibitors – For most waters inhibitors are not required. If interfering ions are present, then prepare Hydroxylamine Hydrochloride Solution by dissolving 4.5 gm of hydroxylamine hydrochloride in 100 ml of 95% ethyl alcohol or isopropyl alcohol.
Standard EDTA Solution – .0.01 M Dissolve 3.723 g EDTA and dilute to 100 ml with distilled water. Standardize against 0.01 M ZnSO4.
Standard ZnSO4 Solution-0. 01M Dissolve 2.8754g of ZnSO4 in distilled water and dilute to 1000 ml.
Preparing Standard Calcium Solution – 1.00 ml = 1.00 mg (CaCO3). Dry analytical grade calcium carbonate (CaCO3) in an oven at 180ºC for 1 hour. Weigh 1.000g, suspend it in distilled water and add concentrated hydrochloric acid AR quality, drop wise slowly to dissolve the solid. Use minimum amount of acid.and let it Boil for a few minutes, after that cool it and add a few drops of methyl red indicator and adjust to orange color with 3N ammonium Hydroxide. Make up to 1000 ml with distilled water.
Standardization: To standardize, accurately weigh to the nearest 1.000 g of Calcium Carbonate (dried at 180ºC). Then dissolve it, cool, add a few drops of methyl red indicator and adjust to Orange color with 3N ammonium Hydroxide and then dilute to a volume of 1000 ml volumetric flask. Take 50 ml Standard Calcium solution in a conical flask; add 1 ml Buffer Solution in it. Then add 1-2 drops of indicator and then titrate it with standard EDTA Solution. After titration the Purple color changes to Sky-Blue color. Note down the burette reading of EDTA Solution (0.01 N). Then calculate the normality of the stock solution.
Procedure:
Take 50 ml or suitable aliquot of sample in 100 ml conical flask. If there is any interference, then add 1 ml hydroxylamine hydrochloride (NH2OH.HCl) solution. Add 1-2 ml buffer solution so as to achieve pH of 10.0 to 10.1. Then add 2-3 drops of eriochrome black T indicator solution, and then titrate with standard EDTA solution stirring rapidly in the beginning and slowly towards the end till end point is reached when solution become red wire to blue.
Calculation: Calculate Total Hardness in the sample as follows:
VTotal Hardness, mg/l = A x N x 100 x 1000/V
Where, A = Volume in ml of the EDTA standard solution used in the titration,
N = Normality of EDTA Solution.
V = Volume of the sample taken for the analysis.
FLOW CHART FOR MEASUREMENT OF TOTAL HARDNESS
Take 50 ml or suitable portion of a sample in a conical flask
Fill the burette with Standard EDTA Solution (0.01 N)
Add 1-2 ml buffer solution
Add 3-4 drops of Eriochrome Black T indicator in sample.
The color of the sample changes to Purple
Then titrate with Standard EDTA Solution (0.01 N)
The color of the sample becomes Sky-Blue
Note the burette reading of the EDTA Solution (0.01 N)
Calculate Total Hardness of the sample in mg/l
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