Hardness Of Water Water is the most important molecule that exists on the Earth. Without water living beings would not be able to live. Water is used for an immeasurable number of things. There are many properties of water, which makes this molecule so unique. One which people overlook is hardness.
Hardness is defined in the Chemistry: The Central Science by Prentice Hall’s as being “water that contains a relatively high concentration of Ca2+, Mg2+, and other divalent cations.” Water containing these ions is not a health hazard; however, it is a problem for industries and households. Therefore, the hardness of water is vital to understand in order to prevent the problems it could cause. For one to have a better understanding of hardness, you must know how water becomes hard or what causes water to become hard. All water that we use is freshwater which is transported through many pipes. The ions Ca2+ and Mg2+ react with water and form insoluble substances which causes blockage and deposits to form.
Some examples of how this affects industries and households are the insoluble substances that form and cause soap scum, scaling in water heaters in factories, and clogging of pipes which transports water places. There are many techniques in which water undergoes in order to decrease the amount of ions in the water before the water comes to your faucet. Although people can take most ions out of the water, not all ions can be removed. The following chart shows the classifications of water and their hardness. In this chart, 1 ppm hardness is equal to 1 part of CaCO3 per million parts water, which is also equal to 1 mg CaCO3 in 1 liter of water. Table A Concentration mg/L CaCO3 Description 0 – 75 soft 75 – 150 moderately hard 150 – 300 hard 300 and up very hard This data is used as a guideline for people to determine how hard/soft the water is. An experimental procedure in Penn State’s version of Chemtrek August 2000-July 2001 on pages 10-12 to 10-20, which was written by Stephen Thompson, is a good procedure to determine the hardness of water. They used two different types of testing in order to compare the different results, the EBT and atomic absorption analysis and EDTA titration.
The first procedure we did was the atomic absorption (AA) analysis. This was done by using a AA spectroscopy. First the water sample was by atomized and then a beam of monochromatic light is fired from a hollow cathrode lamp which emits a light that is set at a certain frequency that has the same frequency energy as the element you are trying to evaluate. The amount of light of the special frequency absorbed by the atomized sample reflects the quantity of the element that is set for. The calibration of the AA Spectroscope is found by putting samples with known concentrations into it and making a graph of the absorptions recorded from them and then by finding a corresponding regression line.
The two following graphs A and B are the graphs with the plots that our instructor, Bin Gu, gave to us in class. Graph A Graph B Therefore, values for samples with unknown concentrations can be derived from the calibration graphs by plugging in the concentration into the equation. For example, with the water sample from Panama City, FL, the Mg concentration found using the AA test was 29.04 mg/L. If we plug that number in then we get the number .5724 which we can compare to the absorbance level which was .5773. It seems that the equation is pretty accurate.
Next, we conducted a Total Dissolved Solids (TDS) testing. This was done by evaporating two drops of water, our sample water and distilled water. We then compared how much residue was left over concluding that there is more ions that are insoluble in the same water than distilled water. The next part of the experiment was to do the EDTA titration test. This test involved adding agents to the water sample and then titrating that solution with EDTA. The first time we did a titration with a known concentration of Ca ions. The next time we did the titrations we used our water sample which gave us the calculation of the concentration of the Ca ions in our sample. This is what we used to compare the hardness of our sample.This titration test procedure consisted of adding a drop of EBT indicator and a drop of NH3/NH4Cl/MgEDTA buffer to a drop of the water sample.
The hard water sample is then titrated with the EDTA. This experiment determines the hardness by first forming a basic solution with the buffer and having the indicator show this. Then, when the EDTA is added, it first reacts with the Ca and forms a colorless chelate, and then the Mg reacts with it forming another colorless chelate. After all of the Mg has reacted with the EDTA, the titration is complete and the indicator shows the solution as a clear blue. The amount of ions in the solution can be determined by setting up a ratio between the drops (volumes) of EDTA and the ions and equating it to the ratio of the concentrations of the two.
This is the formula you should use in order to find the unknown titration: CEDTA VEDTA = CIONS VIONS -Example of calculation 1 -(2.00 x 10-4 M) x 14 drops = CIONS x 1 drop CIONS = .0028 M Since the concentration of the ions is known in Molars, it can be converted to parts CaCO3 per million, the standard hardness unit. The following example is a guidline of how to convert the units. Example of calculation 2- 3.2 x10-3 mol CaCO3 x100 g CaCO3x1000 mg CaCO3=320 mg =320 mg=320 ppm liter mol CaCO3 1 g CaCO3 L 1000 g The last part of the experiment was to do a EDTA titration with our water sample and an added comerical agent water softener. This part of the procedure was to show the effect that water softeners have on the ions in the water. The first softener used was baking soda and the second softener was done by resin beads which reacted with the water by ion exchange, which removed the Ca and Mg ions.
This concluded the lab and with all this information, we compared and made conclusions about our water samples. This experimental procedure was completed in order to find the hardness of samples of water. My group has chosen three different types of tap water from three different areas in order to show the comparison of the hardness of tap water. The samples were taken from East Halls (Hastings) in State College, a house in Pittsburgh, PA (2418 Rolling Farm’s Road), and from a hotel room in Panama City, FL. We assumed for our hypoth …