total hardness is expressed as parts per million of calcium carbonate This

# Total hardness is expressed as parts per million of

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total hardness is expressed as parts per million of calcium carbonate. This means that regardless of the amount of the various components that make up hardness, they can be related to a specific amount of calcium carbonate. That is, hardness is expressed in mg/L or ppm of CaCO 3 . The mg/L of Ca and Mg must be converted into mg/L as CaCO 3 before they can be added. The hardness of water can be classified based on the table below. Table 1. The water hardness scale. Water Hardness ppm CaCO3 Soft 0-20 Moderately soft 20-60 Moderately hard 61-120 Hard 121-180 Very hard >180 In this experiment, total hardness in drinking water is quantitatively determined by complexometric titration using EDTA as titrant. IUPAC has defined 'complexometric titration' as a titration based on reaction of a metal ion with a ligand to form a soluble complex and in which one of the two reactants is used a titrant.[3] Since this type of titration depends upon the combination of ions (other than H + and OH - ) to form a soluble and involved treatment of complex ions such as magnesium, calcium, iron, lead and zinc, some of its application includes determination of ion content in a living cell and introduce these ions into cell in case of deficiencies. Currently, this type of titration is widely used in the medical industry because of the micro liter size sample involved [4]. Water hardness can also be determined using different instruments. A colorimeter is a device that measures the absorbance of particular wavelengths of light by a specific solution. The rate of absorbance is directly proportional to the concentration of the solution given by the Beer-Lambert Law. The concentration of specific ions can be determined using this. Another method is the use of test strips. This chemically impregnated pads change to different color when reacted to a specific ion. There is a color chart that represents color and their various concentrations. [5] The objective of the experiment is for the student to be able to apply the concept of complexometric titration in the determination of total hardness in drinking water. For the standardization of the 0.01 M EDTA solution, 10 mL of the 0.0050 M working standard CaCO3 solution was measured and placed into each of three 250-mL Erlenmeyer flasks, then added with 75 mL distilled water. Three mL of the NH3-NH4+ buffer solution was put into the solution, followed by 2-3 drops of the EBT indicator. Titration of the solution with the standard EDTA solution followed immediately after, which must be done until a color change from wine red to clear blue is observed. In the analysis of the Viva! Mineralized water sample and tap water sample, 50 mL of the both water sample was measured into each of three 250 mL Erlenmeyer flasks. The same procedure from the standardization process was followed. Note that the type of sample water used is mineralized or spring water, since natural minerals (e.g., calcium, magnesium, iron) are still present. Purified

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water and distilled water cannot be titrated since contaminants, including minerals all
• Fall '17
• Drinking water, Hard water, Calcium carbonate

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