The Determination of the Concentration of Hard Water Ions by the Titration of EDTA
Lab partners: Heidi Kiziah, Leonie Hamel
University of Central Florida, CHM 2046L
December 3rd, 2015
Abstract. The “hardness” of water is a common dilemma attributed by high concentrations of metals such as calcium and magnesium. This is a result of the properties of water; because it is a good solvent, impurities are easily dissolved. As water moves through soil and rock, it dissolves minute amounts of minerals and holds them in solution. Although it is not hazardous to health, hard water is a nuisance to both industrial and domestic water consumers. Mineral buildup on plumbing fixtures, poor soap and detergent performance, and a contribution…
This reaction was an example of coordination chemistry. In coordination chemistry, transition metals bind with ions or certain compounds in aqueous solutions. These ions are ligands, while the compound in its entirety is known as a coordination complex. EDTA is one such ligand. In its nonprotonated form the EDTA has extra, unpaired electrons on the four oxygen atoms that have single bonds with the carbons and on the two nitrogen atoms. The unpaired electrons, the two nitrogens and four oxygens, make these coordinate covalent bonds (3). The buffer solution with a pH of 10 that added to each solution served a crucial role in the reaction. The buffer provided a basic pH that stimulated the deprotonation of EDTA so that it was able to bind the metal ions that were present in the…
Table 1. Volume of EDTA used Depending on the Sample of Water EDTA coordinated with the MgCl2 metal ions added to both samples and the hard water metal ions present in TAP water.
Sample TAP Water DI Water
Volume of 0.005 M EDTA used in titration 150 mL 75 mL
The data in the table above was used in the determination of the calculation of metal ions in the samples of both TAP and DI water.
Primarily, hard water consists of magnesium and calcium. Therefore the ratio of magnesium to calcium ions was inferred to be 50/50. The average molar mass of the molar mass of Magnesium (24.305 g/mol) and the molar mass of Calcium (40.078 g/mol) was calculated to be 32.192 g/mol. This calculated average molar mass was used as the molar mass of the metal that was present in the sample. The concentration of metal that was present in the TAP water was solved by the following calculations:
150 mL EDTA * (1 L/ 1000 mL) * (0.005 M) = 0.00075 moles of metal
(0.00075 moles/ 0.050 L) = 0.015 moles/ L
0.00075 moles of metal * (32.192 g/ 1 mol) * (1000 mg/ 1 g) = 24.144 mg
The concentration of metal that was present in the DI water was solved by the following calculations:
75 mL EDTA * (1L/1000 mL) * 0.005 M = 0.000375…