Sacramento Tap Water Lab Report
Sacramento tap water reveals ion concentrations of various different dissolved minerals such as calcium (Ca2+) and magnesium (Mg2+). These concentrations are a result of mineral deposits in local lakes and rivers. Perma Pure, a gas conditioning products manufacturing company, simplifies the mechanism of ion exchange by explaining that water is a solvent that dissolves most ionic bonds when exposed to compounds ("The Mechanism of Ion Exchange"). Therefore, as tap water passes through rocks it will pick up several different minerals resulting in hard water. As reported by the USGS water science school, calcium carbonate concentrations from 0 to 60 parts per million (ppm) are considered soft, while 61 to 120 ppm is medium, and anything past 121 ppm is classified as hard water (Perlman). In this experiment, a sample of Sacramento tap water was tested for its ion concentrations of Ca2+, Mg2+, chloride (Cl-), nitrate (NO3-), and sulfate (SO42-), which will give insight on potential negative and positive effects of using the tap water. If the concentrations of
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the water are too high then hard water may ruin several daily items and activities. For instance, as explained by Apec Water company, hard water may clog pipelines, ruin household appliances, make hair feel sticky, and ruin clothing (“Hard and Soft Water Explained”). However, hard water does contain several essential minerals making it the more beneficial choice for drinking water with the exception of a high nitrate concentration. While all high ion concentrations have their defects, too much nitrate is specifically harmful for infants as it impairs the bloods ability to carry oxygen (“Chemical Contaminant Rules”). Therefore, the Environmental Protection Agency (EPA) has established a standard of 10 ppm for nitrate in water.
This experiment used two methods, atomic absorption spectroscopy (AAS) and ion chromatography (IC), to analyze ion concentrations in tap water. AAS was used to analyze Ca2+ and Mg2+ ions. In flame AAS, a sample is aspirated into a flame which is lined with a lamp giving a beam of light at the wavelength for a specific element (Harris & Lucy, chap. 21). As atoms jump from ground to excited state, the metal atoms absorb light from the beam which then gives the absorbance of the substance from the decrease of the beam’s intensity. Considering a calibration curve can be made with absorption and concentration, the unknown tap water sample was analyzed by running a series of calibrations standards through the AAS. This curve, also known as the Beer’s law plot, needs to be as linear as possible in order to accurately determine the ion concentrations in the tap water sample. Therefore, five dilutions were made for each element across the ranges of 1 to 10 ppm for Ca2+ and the range of 0.1 to 1 ppm for Mg2+ in order to achieve a linear plot. The concentration of the Ca2+ stock was calculated from a known concentration of a previous experiment assuming 90% Ca2+ and 10% Mg2+, resulting in a 541 ppm Ca2+. Since only volumetric glassware available was used to make dilutions, a table of calculations were made to easily compare possible dilutions. Five dilutions of 1.08, 2.16, 5.41, 6.49, and 8.66 ppm were made for Ca2+. A semi-stock solution of Mg2+ was made by diluting the original stock solution of Mg2+ 1:100 to achieve a concentration of 99.6 ppm. Which then was used to calculate and compare possible dilutions and five dilutions of 0.0996, 0.3984, 0.4980, 0.7969, and 0.996 ppm were made for Mg2+. Tap water dilution factors were calculated from average concentrations found online. The Ca2+ sample was diluted 25:100 to give a concentration of 5.5 ppm, while the Mg2+ sample was diluted 5:100 to make a 0.65 ppm sample. Next all standards were run on the AAS before the linearity of the absorbance and concentrations of the standards could be checked in excel, and finally the tap water sample was analyzed to give the absorbance. Lastly, Ca2+ and Mg2+ ions concentrations in the tap water sample were determined using Beer’s law.
The second experimental method, IC, focused on Cl-, NO3-, and SO42- ions in the sample.
In IC, the analyte is injected into the eluent, which then passes through a column and separates ions between a stationary and mobile phase (Harris & Lucy, chap. 26). Depending on how well the anions stick to the column will determine the retention order of the element. Since the anions that are smaller in size and have higher negative charges will stick to the stationary phase the best, the first peak visible will be Cl-, then NO3-, and lastly SO42-. Unlike the AAS method describe above, the IC tap water sample was not diluted prior to running the sample. Once the sample was analyzed and all three peaks of the elements were found. A one point calibration curve was made from the results of the instructor’s standard by plotting peak area against concentration, which was lastly used to determine the concentration of each
element.
the water are too high then hard water may ruin several daily items and activities. For instance, as explained by Apec Water company, hard water may clog pipelines, ruin household appliances, make hair feel sticky, and ruin clothing (“Hard and Soft Water Explained”). However, hard water does contain several essential minerals making it the more beneficial choice for drinking water with the exception of a high nitrate concentration. While all high ion concentrations have their defects, too much nitrate is specifically harmful for infants as it impairs the bloods ability to carry oxygen (“Chemical Contaminant Rules”). Therefore, the Environmental Protection Agency (EPA) has established a standard of 10 ppm for nitrate in water.
This experiment used two methods, atomic absorption spectroscopy (AAS) and ion chromatography (IC), to analyze ion concentrations in tap water. AAS was used to analyze Ca2+ and Mg2+ ions. In flame AAS, a sample is aspirated into a flame which is lined with a lamp giving a beam of light at the wavelength for a specific element (Harris & Lucy, chap. 21). As atoms jump from ground to excited state, the metal atoms absorb light from the beam which then gives the absorbance of the substance from the decrease of the beam’s intensity. Considering a calibration curve can be made with absorption and concentration, the unknown tap water sample was analyzed by running a series of calibrations standards through the AAS. This curve, also known as the Beer’s law plot, needs to be as linear as possible in order to accurately determine the ion concentrations in the tap water sample. Therefore, five dilutions were made for each element across the ranges of 1 to 10 ppm for Ca2+ and the range of 0.1 to 1 ppm for Mg2+ in order to achieve a linear plot. The concentration of the Ca2+ stock was calculated from a known concentration of a previous experiment assuming 90% Ca2+ and 10% Mg2+, resulting in a 541 ppm Ca2+. Since only volumetric glassware available was used to make dilutions, a table of calculations were made to easily compare possible dilutions. Five dilutions of 1.08, 2.16, 5.41, 6.49, and 8.66 ppm were made for Ca2+. A semi-stock solution of Mg2+ was made by diluting the original stock solution of Mg2+ 1:100 to achieve a concentration of 99.6 ppm. Which then was used to calculate and compare possible dilutions and five dilutions of 0.0996, 0.3984, 0.4980, 0.7969, and 0.996 ppm were made for Mg2+. Tap water dilution factors were calculated from average concentrations found online. The Ca2+ sample was diluted 25:100 to give a concentration of 5.5 ppm, while the Mg2+ sample was diluted 5:100 to make a 0.65 ppm sample. Next all standards were run on the AAS before the linearity of the absorbance and concentrations of the standards could be checked in excel, and finally the tap water sample was analyzed to give the absorbance. Lastly, Ca2+ and Mg2+ ions concentrations in the tap water sample were determined using Beer’s law.
The second experimental method, IC, focused on Cl-, NO3-, and SO42- ions in the sample.
In IC, the analyte is injected into the eluent, which then passes through a column and separates ions between a stationary and mobile phase (Harris & Lucy, chap. 26). Depending on how well the anions stick to the column will determine the retention order of the element. Since the anions that are smaller in size and have higher negative charges will stick to the stationary phase the best, the first peak visible will be Cl-, then NO3-, and lastly SO42-. Unlike the AAS method describe above, the IC tap water sample was not diluted prior to running the sample. Once the sample was analyzed and all three peaks of the elements were found. A one point calibration curve was made from the results of the instructor’s standard by plotting peak area against concentration, which was lastly used to determine the concentration of each
element.