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Experiment 8 Determination of the Hardness of Natural Waters— A: Conventional EDTA Complexometric Titration B: Commercial Test Kit Determination QObjectives—the objectives of this experiment are: 1. To measure the hardness of environmental waters from several sites to determine the effect of location on hardness 2. To show how hardness may be readily measured in the field using a test kit. Introduction—The hardness of water was originally defined in terms of its ability to precipitate soap. Calcium and magnesium ions are the principal causes of hardness in water, although iron, aluminum, manganese, strontium, zinc, and hydrogen ions are also capable of producing the same effect. The total hardness of water is now defined as the amount of calcium and magnesium present and is expressed as ppm calcium carbonate. The procedure for determining both calcium and magnesium, when present together, is found in many schemes of applied analysis, including the analysis of minerals, blood serum, and food, and is the standard method for determining water hardness. The hardness test is one of the most commonly performed analyses in the water industry. High levels of hardness are undesirable and must be removed before the water is used by the beverage, laundry, metal- finishing, dying and textiles, food, and paper pulp industries. Hardness levels greater than 500 ppm calcium carbonate are undesirable for domestic use and most drinking water supplies average about 250 ppm. Table 8-1 lists the various classes of hardness. Table 8-1 Classes of Hardness Based on Hardness Range HARDNESS RANGE HARDNESS (ppm CaCO,) DESCRIPTION 0-50 Soft 31-150 Moderately Hard 151-300 Hard >300 Very Hard Source: G. Tchobanoglous and E. D. Schroeder, Water Quality, Addison-Wesley, Reading, MA, 1985. 101 
