Complexometric Titration: Determination of Calcium

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EXPERIMENT 2 COMPLEXOMETRIC TITRATION: DETERMINATION OF CALCIUM 1. Abstract In this experiment, the hardness of a water sample which is tap water will be determined by using complexometric EDTA titration method. The EDTA solution of 0.010M was first standardized with calcium carbonate, CaCO3. Eriochrome Black T was used as an indicator, which changes from red wine(colour of Eriochrome Black T bound to a metal ion) to blue(colour of free Eriochrome Black T ion) in the presence of excess EDTA. After standardizing the EDTA, the average molarity was found to be 0.01054M. Meanwhile, the calcium concentration in tap water was found to be 6.1930 ppm ± 1.76. 2. Introduction Calcium salts dissolving from rocks, minerals cause water hardness. The water hardness poses problems such as the need for larger quantities of soap for washing, scale formation in boilers, kettles and water pipes. Thus, it causes soap scum, clog pipes and clog boilers. The determination of water hardness is very useful to measure the quality of water for households and industrial uses. Complexation reaction involves reactions of complex ions or undissociated neutral molecules in a solution. The most important requirement is that, the complex is extremely soluble. These complexes or coordination compounds are formed when metal ions react with electron-pair donors. These donor species, also called ligands, must have at least one pair of unshared electrons available for covalent bond formation. A chelate is produced when a metal ion coordinates with two or more donor groups of a single ligand to form a five- or six-member heterocyclic ring. In this experiment, EDTA is used as the titrant. It is a chelating agent; capturing the metal ions contained in the water, binding them to itself very tightly and therefore softening the water. It can form several bonds to a metal ion,

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