# Complexometric Determination of Water Hardness

Topics: Calcium, Hard water, Calcium carbonate Pages: 2 (400 words) Published: November 26, 2012
Complexometric Determination of Water Hardness
Abstract: Create a standardized EDTA solution for use as a titration solution to determine the hardness of water from a single random sample. Introduction: Using a calibrated EDTA solution to determine water hardness from a random sample. Essentially the Na2EDTA solution reacts one to one with the mineral content of a sample of tap water and by use of a standardized solution a ppm estimation can be obtained for the hardness of water. Current knowledge in this area is well understood and procedures used follow generally accepted guidelines. Method: First the calibration was completed using an approximately .7340g Na2EDTA/500mL solution. A 1.000g/L calcium ion solution was used as the primary standard with approximately 3mL of ammonium chloride as a buffer and Erichrome Black T as the indicator solution. Three titrations were performed to ensure accuracy of the molarity of the Na2EDTA solution. The 1.000g/L calcium ion solution had to be converted to M so 1g/L/100.1g=.009990M calcium ion solution. Titration 1: 10.00mL CaCO3; .00999MCaCO3X.0100L= .0000999mol CaCO3 .0000999mol EDTA/.002507L = .00398M Na2EDTA

Titration 2: 10.00mL CaCO3; .00999MCaCO3X.0100L= .0000999mol CaCO3 .0000999mol EDTA/.02339L = .004271M Na2EDTA
Titration 3: 9.95mL CaCO3; .00999MCaCO3X.0100L= .0000994mol CaCO3 .0000994mol EDTA/.02367L = .004196M Na2EDTA
Since the first titration is so far out from the other two it was thrown out giving an average result of .004233M Na2EDTA Sample B was used in this experiment with at 25mL and three titrations were performed to ensure accuracy with the same buffer solution (appx 3mL ammonium chloride @ pH10). A magnetic stirrer and standard burette were used in the procedure with a read accuracy to .01mL. Eriochrome Black T was the indicator solution.

Results:
Titration 1: 12.52mL Na2EDTA; .00423M Na2EDTA x .01252L = .0000530 mol .0000530mol/.02496L = .00212M hardness
Titration 2: 12.19mL Na2EDTA;...