Water Hardness Testing by Complexometric Determination of Calcium

Abstract

Ethylenediaminetetraacetate (EDTA) complexes with numerous mineral ions, including calcium and magnesium. This reaction can be used to determine the amount of these minerals in a sample by a complexometric titration. Endpoints in the titration are detected using indicators that change color when they complex with mineral ions. A major application of EDTA titration is testing the hardness of water, for which the method described is an official one. Hardness of water also can be tested by a more rapid test strip method. The commercial test strips contain EDTA and an indicator chemical to cause a color change when the calcium and magnesium in water react with the EDTA. In this laboratory exercise, hardness of water is determined by both the EDTA titration method and with Quantab® test strips.