Determining Calcium Ion Concentration in Water by Complexometric Titration
- Calcium and magnesium ions dissolved in water cause water hardness.
- Ethylenediaminetetraacetic acid (EDTA), shown on the right in its deprotonated form, is commonly used in a titration to determine the concentration of Ca2+ and Mg2+ ions in water because both ions form complexes with EDTA.
- In order to determine the concentration of Ca2+ in water, the Mg2+ must be removed first, usually by precipitation.
- The titration with EDTA then determines the concentration of Ca2+ remaining in the water.
- The complex formed between Ca2+ and EDTA is colourless and soluble, so a suitable indicator must be used to show the endpoint of the titration.
- The concentration of Ca2+ in water can then be calculated.