Temporarily and Permanently Hard Water

PURPOSE OF EXPERIMENT Study some chemical properties some ways for softening hard water. 

Water containing Ca2+, Mg2+, and Fe2+ ions is known as hard water because, when soap is first added, a lather cannot be obtained. Common soap made from animal fat or vegetable oil is a mixtures of sodium and potassium salts of palmitic, stearic, and oleic acids. These salts are soluble and are dissociated in water. They readily form a lather with pure water and are widely used for cleansing purposes. However, Ca2+, Mg2+, and Fe2+ ions react with soap and form insoluble salts that separate as slimy, sticky precipitates. For example, Ca2+ ions react with stearate ions as follows. 

Before soap can form a lather or act as a cleansing agent, Ca2+, Mg2+, and Fe2+ ions must be removed by precipitation from the solution. Hence, the use of hard water for laundry purposes is very wasteful of soap, and the sticky residue left is undesirable. 

When hard water is used in steam boilers where the water is heated and evaporated, any nonvolatile substances that are in solution in the water will precipitate on the walls of the boiler tubes when the water becomes saturated. In time, these tubes become thickly coated or even plugged with this deposit or scale. Only a 0.15-cm thickness of boiler scale lowers the efficiency of heat transfer by about 10.%. 

In this experiment you will prepare temporarily hard water study some of the chemical properties of soft, temporarily hard, and permanently hard water and study various processes available for softening hard water. The hardness of different water samples will be tested quantitatively by determining the volume of soap solution that must be added to a given volume of water in order to obtain a lather. Moreover, hard water will be treated by several methods designed to soften it, and the treated water will be titrated with soap solution to test the effectiveness of the methods. A study of the hardness of water, the action of soaps, and methods for softening water will illustrate characteristic chemical reactions and important differences in solubilities of some compounds of alkali metals and the alkaline earth metals. In addition, you will become familiar with a laboratory preparation for and properties of carbon dioxide gas. 

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