The purpose of this experiment is to explore thehardness of the water on campus. Hard water hasbeen a problem for hundreds of years. One of theearliest references to the hardness or softness ofwater is in Hippocrates discourse on water qualityin Fifth century B.C. Hard water causes manyproblems in both in the household and in theindustrial world. One of the largest problems withhard water is that it tends to leave a residue whenit evaporates. Aside from being aestheticallyunpleasing to look at, the build up of hard waterresidue can result in the clogging of valves, drainsand piping.
This build up is merely theaccumulation of the minerals dissolved in naturalwater and is commonly called scale. Other thanclogging plumbing, the build up of scale poses alarge problem in the industrial world. Many thingsthat are heated are often cooled by water runningthru piping. The build up of scale in these pipescan greatly reduce the amount of heat the coolingunit can draw away from the source it is trying toheat.
This poses a potentially dangerous situation.
The build up of excess heat can do a lot ofdamage; boilers can explode, containers can meltetc. On the flip side of the coin, a build up of scaleon 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 heatthe kettle to the necessary temperature. In theindustrial world, this could amount to large sums ofmoney being thrown into wasted heat. In additionto clogging plumbing and reducing heatingefficiency, the build up of hard water alsoadversely affects the efficiency of many soaps andcleansers. The reason for this is because hardwater contains many divalent or sometimes evenpolyvalent ions. These ions react with the soapand although they do not form precipitates, theyprevent the soap from doing it’s job. When thepolyvalent ions react with the soap, they form aninsoluble soap scum. This is once again quiteunpleasing to look at and stains many surfaces.
The sole reason for all these problems arising fromhard water is because hard water tends to havehigher than normal concentrations of theseminerals, and hence it leaves a considerableamount more residue than normal water. Theconcentration of these minerals is what is knownas the water’s Total Dissolved Solids or TDS forshort. This is merely a way of expressing howmany particles are dissolved in water. The TDSvary from waters of different sources, howeverthey are present in at least some quantity in allwater, unless it has been passed through a specialdistillation filter. The relative TDS is easilymeasured by placing two drops of water, onedistilled and one experimental on a hotplate andevaporating the two drops. You will notice that theexperimental drop will leave a white residue. Thiscan be compared to samples from other sources,and can be used as a crude way of measuring therelative TDS of water from a specific area. Themore residue that is left behind, the more dissolvedsolids were present in that particular sample ofwater. The residue that is left, is in fact, the solidsthat were in the water. Another, perhaps morequantitative way of determining hardness of wateris by calculating the actual concentrations ofdivalent ions held in solution. This can be done oneof two ways. One is by serially titrating the waterwith increasing concentrations of indicator forMg++ and Ca++ (we will be using EDTA). Thiswill tell us the approximate concentration of alldivalent ions. This method of serial titrations isaccurate to within 10 parts per million (ppm) .
Another possible method for determining thehardness of water is by using Atomic AbsorptionSpectrophotometry or AA for short. AA is amethod of determining the concentrations ofindividual metallic ions dissolved in the water. Thisis accomplished by sending small amounts ofenergy thru the water sample. This causes theelectrons to assume excited states. When theelectrons drop back to their ground states, theyrelease a photon of energy. This photon ismeasured by a machine and matched up to thecorresponding element with the same E as wasreleased. This is in turn is related to the intensity ofthe light emitted and the amount of light absorbedand based on these calculations, a concentrationvalue is assigned. A quick overview of how theatomic absorption spectrophotometer worksfollows. First, the water sample is sucked up.
Then the water sample is atomized into a fineaerosol mist. This is in turn sprayed into anextremely high intensity flame of 2300 C which isattained by burning a precise mix of air andacetylene. This mixture burns hot enough toatomize everything in the solution, solvent andsolute alike. A light is emitted from a hollowcathode lamp. The light is then absorbed by theatoms and an absorption spectrum is obtained.
This is matched with cataloged known values toattain a reading on concentration. Because thereare so many problems with hard water, wedecided that perhaps the water on Penn State’scampus should be examined. My partners and Idecided to test levels of divalent ions (specificallyMg++ and Ca++ ) in successive floors ofdormitories. We hypothesized that the upper leveldormitories would have lower concentrations ofthese divalent ions because seeing as how they areboth heavy metals, they would tend to settle out ofsolution. The Ca++ should settle out first seeinghow it is heavier than the Mg++, but they will bothdecrease in concentration as they climb to higherfloors in the dormitories. PROCEDURE Wecollected samples from around Hamilton Halls,West halls. In order to be systematic, we collectedsamples in the morning from the water fountainsnear the south end of the halls. We collected watersamples from each floor in order for comparison.
The reason we collected them in the morning wasso that the Mg++ and Ca++ would be innoticeable quantities. We then went about andtested and analyzed via serial titrations and viaAtomic Absorption Spectrophotometry. We alsoobtained a TDS sample merely for the sake ofcomparison, and to ensure that were in factdissolved solids in our water samples (withoutwhich this lab would become moot). For the serialtitration, we merely mixed the water sample withEBT, and then with increasing concentrations ofEDTA. The EBT served as an indicator to tell uswhen the concentrations of the EDTA and thedivalent ions in solution were equal (actually it toldus when Mg++ was taken out of solution but thatserved the same purpose). This allowed us to findthe concentration of the divalent ions dissolved insolution. Based on this, we calculated the partsper million and the grains per gallon for each watersample. Finally, we took an AA reading for eachsample. This gave us absorption values andconcentration values for each of the two mainmetals we were observing; Ca++ and Mg++. Wethen plotted a graph of Atomic AbsorptionStandards. These were values given to us by theAA operator. These values helped us to calibratethe machine. The parts per million that we find willbe based on plugging in the reported absorptionvalue into the resulting curve from the graph ofthese values. The resulting concentration was usedas the final value for the hardness for thatparticular sample. All calculations and conclusionswere done based on these final values obtained forthe concentration of Ca++ and Mg++.
Cite this Chemistry Of Natural Water
Chemistry Of Natural Water. (2019, Apr 05). Retrieved from https://graduateway.com/chemistry-of-natural-water/