The Chemistry of Natural Water INTRODUCTION The pu

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The Chemistry of Natural Water  INTRODUCTION  The purpose of this experiment is to explore the hardness of the water on campus. Hard water has been a  problem for hundreds of years.  One of the earliest references to the hardness or softness of water is in  Hippocrates discourse on water quality in Fifth century B.C.  Hard water causes many problems in both in  the household and in the industrial world.  One of the largest problems with hard water is that it tends to  leave a residue when it evaporates.  Aside from being aesthetically unpleasing to look at, the build up of  hard water residue can result in the clogging of valves, drains and piping.  This build up is merely the  accumulation of the minerals dissolved in natural water and is commonly called scale.    Other  than clogging plumbing, the build up of scale poses a large problem in the industrial world.  Many  things that are heated are often cooled by water running thru piping.  The build up of scale in these pipes  can greatly reduce the amount of heat the cooling unit can draw away from the source it is trying to heat.   This poses a potentially dangerous situation.  The build up of excess heat can do a lot of damage; boilers  can explode, containers can melt etc.  On the flip side of the coin, a build up of scale on an object being  heated, a kettle for example, can greatly reduce the heat efficiency of the kettle.  Because of this, it takes  much more energy to heat the kettle to the necessary temperature.  In the industrial world, this could  amount to large sums of money being thrown into wasted heat.  In addition to clogging plumbing and reducing heating efficiency, the build up of hard water also  adversely affects the efficiency of many soaps and cleansers.  The reason for this is because hard water  contains many divalent or sometimes even polyvalent ions.  These ions react with the soap and although  they do not form precipitates, they prevent the soap from doing it's job.  When the polyvalent ions react  with the soap, they form an insoluble soap scum.  This is once again quite unpleasing to look at and stains  many surfaces.  The sole reason for all these problems arising from hard water is because hard water tends to have higher  than normal concentrations of these minerals, and hence it leaves a considerable amount more residue  than normal water.  The concentration of these minerals is what is known as the water's Total Dissolved  Solids or TDS for short.  This is merely a way of expressing how many particles are dissolved in water.   The TDS vary from waters of different sources, however they are present in at least some quantity in all  water, unless it has been passed through a special distillation filter.  The relative TDS is easily measured  by placing two drops of water, one distilled and one experimental on a hotplate and evaporating the two  drops.  You will notice that the experimental drop will leave a white residue.  This can be compared to  samples from other sources, and can be used as a crude way of measuring the relative TDS of water from a  specific area.  The more residue that is left behind, the more dissolved solids were present in that  particular sample of water.   The residue that is left, is in fact, the solids that were in the water.    Another, perhaps more quantitative way of determining hardness of water is by calculating the actual  concentrations of divalent ions held in solution.  This can be done one of two ways. One is by serially   titrating the water with increasing concentrations of indicator for Mg++ and Ca++ (we will be using  EDTA).  This will tell us the approximate concentration of all divalent ions.   This method of serial  titrations is accurate to within 10 parts per million (ppm) .    Another possible method for determining the hardness of water is by using Atomic Absorption  Spectrophotometry or AA for short.  AA is a method of determining the concentrations of individual  metallic ions dissolved in the water.  This is accomplished by sending small amounts of energy thru the  water sample.  This causes the electrons to assume excited states.  When

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