Project 4 - Lab report PDF

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Project 4: Fluoride in our Drinking Water

Pre-Lab Questions:

1. Fluoride strengthen tooth enamel and replaces essential minerals that are lost in teeth that have started to decay. Fluorinated water supplies and toothpaste are so efficient that they have been credited as part of the dramatic decrease in tooth decay and cavity occurrence that has taken place over the past decades. Although nearly all water naturally contains a small amount of fluoride, the amount is not always at what the U.S. Centers for Disease Control

and Prevention (CDC) considers to be the optimal level for tooth decay prevention. The CDC and other public health experts state that fluoride in the amount of 0.7 milligrams per liter in water helps prevent tooth decay. To reach this recommended level, many municipal water systems add fluoride to the local drinking water supply, a process known as water fluoridation. The CDC named community water fluoridation one of 10 great public health achievements of the 20th century. According to the American Dental Association (ADA), studies show that fluoride in community water systems prevent at least 25 percent of tooth decay in children and adults alone, even in an era with widespread availability of fluoride from other sources, such as fluoride toothpaste.[1]

2. I think that the purpose of the Journal of Chemical Education is to provide updates on different researches on chemical education. Various scientists have the chance to present their research on this journal. Its target audience includes instructors of chemistry from middle school through graduate school and some scientists in different fields (ex: industry, commerce, and government). They provide to the audience peer reviewed articles, and multiple research projects.

3. The optimum range of fluoride in drinking water in USA is 0.7 to 1.2 ppm. The source cited by the authors is “Rethinking Fluoride?” by the Doctor Andrew Weil.

4. Prepare three 50-mL fluoride standards (0.1, 1.0, and 10.0 ppm).

Rinse electrode with DI water to prevent any solution carry over after h l di

Add 25 mL of TISAB buffer to each standard and make the volume 50 mL by adding DI Dilute samples 1:1 with TISAB (25 mL sample/25 mL TISAB)

Prepare a blank consisting of 25 mL of TISAB and 25

Collect 7 samples of water

Immerse electrode into de solution. Record readings after it stabilizes (usually

5. The authors measured that El Paso Water contained 0.9 ppm of fluoride. El Paso Water Utilities test results averaged between 0.6 and 1.1 ppm fluoride in water sampled from that area of the city. West El Paso well water was reported to be 0.8 ppm fluoride. Therefore, the fluoride concentrations of the samples collected were found to be in the expected range.[2]

Procedures:

Part 1: Using a graduated cylinder, measure 20 mL of the four given Fluoride solutions into 4 separate 50 mL plastic beakers.

Add 10 mL of the Fbuffer into each of the plastic beakers. Stir.

Add 10 mL of the TISAB concentrate to each of the plastic beakers. Stir. Notice that there is a 1:1 ratio between the total amount of the F- buffer + TISAB concentrate and the Fluoride

Collect 3 20mL samples of water for analysis. (DI water, tap water and fountain water)

Add 10 mL of the Fbuffer into each of the plastic beakers. Stir.

Create a calibration curve of Potential (mV) vs. Log [F-] with the collected data. Find the equation of the given graph.

Measure the potential readings of each of the solutions by inserting the electrodes inside the plastic beakers and recording the readings after it stabilizes. (Make sure to rinse and dry properly the electrodes before dipping them into a new solution.)

Add 10 mL of the TISAB concentrate to each of the plastic beakers. Stir.

Measure the potential readings of the unknows by inserting the electrodes inside the plastic beakers and recording the readings after it stabilizes. (Rinse and dry properly the electrodes before measuring a new sample)

Clean all utensils used and dispose properly all substances.

Find the concentration of the unknowns by plugging each reading on the equation previously found and solve for [F-].

Data and Calculations:

Table 1. Potential Readings (mV) for the Given Fluoride Solutions: [F-] of solution 0.2375 ppm 0.9500 ppm 9.500 ppm 23.7500 ppm

Potential (mV) of solution 241 mV 214 mV 163 mV 136 mV

Graph 1. Calibration Curve for the Determination of Fluoride in Water:

Table 2. Potential Readings (mV) for the Water Samples: Sample DI H2O Tap H2O Fountain H2O

Potential (mV) of solution 254 mV 229 mV 234 mV

Calculations for the [F-] on the water sample: y= -52.983x + 210.68; where y is the potential of solution (mV) and x is the log of the [F-] in the sample. [F- ]in DI H2O : 254= -52.983x+ 210.68 254 −210.68 = -0.81762= log [F-] x= −52.983 [F-]= 10-0.81762 [F-]= 0.152 ppm [F- ]in Tap H2O: 229= -52.983 x + 210.68 229 −210.68 x= = -0.34577= log [F-] −52.983 [F-]= 10-0.34577 [F-]= 0.451 ppm [F- ]in Fountain H2O: 234= -52.983 x + 210.68

234 −210.68 −52.983 [F ]= 10-0.44014 [F-]= 0.363 ppm x=

= -0.44014= log [F-]

Table 3. Final [F-] on the water sample: Sample DI H2O Tap H2O Fountain H2O

[F-] of solution (ppm) 0.152 ppm 0.451 ppm 0.363 ppm

Discussion/ Conclusion: The purpose of this laboratory experiment was to quantify the fluoride concentrations of three given water samples by using ion-selective electrodes and developing a calibration curve with standard fluoride solutions. In order to accomplish this, the potential (mV) of four standard fluoride solutions of different concentrations were measured. From the obtained results, a calibration curve of log [F-] in solution vs. potential was created, and the equation of the graph was obtained. Consequently, the potential of the three unknown [F-] in water samples were measured, and the potential values obtained were plugged on the equation of the line to calculate their fluoride concentrations. According to the results, the fluoride concentration in DI water was 0.152 ppm, in tap water was 0.451 ppm, and in fountain water was 0.363 ppm.

These values are not within the optimum range of fluoride in drinking water in USA (0.7 to 1.2 ppm). According to the Florida Department of Health, 100% of the population in MiamiDade is served with fluoridated water, and the optimal fluoride concentration is 0.7 ppm[3]. However, the values obtained for tap water (0.451 ppm) and fountain water (0.363 ppm) were far off the actual value. It makes sense that fluoride concentration for DI water was the lowest since the distillation process diminishes the fluoride ions concentration in the water. Even though an exact value for the DI water fluoride content was not provided by the manufacturer, the obtained results were compared to other DI water companies to validate the accuracy of the results. According to the three companies referred to, (PureTec, Evoqua, Water One, Inc.) there should be no fluoride ions on the DI water. However, the experiment revealed a concentration of 0.152 ppm. The discrepancies during this lab may be accounted by different sources of errors that affected the outcomes of the experiment. One possible error may be the use of contaminated equipment (electrodes, beakers). If the utensils are not properly cleaned before usage, there can be residuals from other experiments that might have reacted with the new solutions, affecting the potential and concentration of the compounds. Another possible error is the improper calibration of the pH meter used and the volumetric pipets. These systematic errors may affect the accuracy and precision of the results. In addition, the electrodes may not have been dipped in the solution long enough, obtaining an inaccurate potential reading for the solutions. Miscalculations and wrong data collection could have also affected the obtained results. The technique used in this lab to quantify the concentration of fluoride in water was effective. Using an Ion Selective Electrode (ISE) is an unexpensive and easy technique; the experimental procedure was relatively fast in comparison to other labs done in this class. In

addition, the electrodes provide real-time measurements, meaning that it can monitor the change of concentration of fluoride with time. In order to measure the [F-] on different examples, the electrodes only had to be rinsed and dried, which is a fast technique that does not involve the preparation of complicated chemical set-up. In addition to the method used in this lab to find the fluoride concentration in water—using an ion-selective electrode and creating a calibration curve—there are other methods that could be used to accomplish the same goal. One of them could be ion chromatography (IC). In this technique, the concentration of ionic species is measured by separating them based on their interactions with a resin. The ionic species are separated based on type and size. The solutions pass through a pressurized chromatographic column where ions are absorbed by column constituents. As an ion extraction liquid runs through the column, the absorbed ions begin separating from the column. The retention time of different species determines the ionic concentrations in the sample[4]. This lab was very important because it explored different techniques—such as using Ion Selective Electrodes—that are important in different industries. This is used in the analysis of environmental samples, groundwater monitoring, and biomedical laboratories. In addition, this lab analyzed the fluoride content in water, which is very important in order to ensure that water is safe for consumption and people can benefit from it.

References: [1] “The Superhero that Lives Inside Your Mouth” https://www.mouthhealthy.org/en/fluoridesuperhero American Dental Association (2018) [2] “Introduction to Analytical Chemistry Lab Manual” https://canvadocs.instructure.com/1/sessions/eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJjIj oxNTU4Mjk4MjA2OTA2LCJkIjoiTWF4Z0ZGakFRNnVxRW1PRE5HV0s5UDgxWHRycWlwI

iwiZSI6MTU1ODMzNDIwNiwiciI6InBkZmpzIiwibCI6ImVuIiwiZyI6InVzLWVhc3QtMSIsIm giOnt9LCJpYXQiOjE1NTgyOTgyMDYsImV4cCI6MTU1ODMzNDIwNX0.7iti78VaAcaxaRV c07JVvBU9eQ3TuMSiJq6QdZbqlpTfYFdOBhBvCgqA-OVJJk2_VQfEF9AFZ0uk4e_RGZamA/view?theme=dark Department of Chemistry and Biochemistry (2019, Summer) [3] “Community Water Fluoridation” http://www.floridahealth.gov/programs-andservices/community-health/dental-health/fluoridation/index.html Florida Health (2019) [4] “Ion chromatography” https://serc.carleton.edu/microbelife/research_methods/biogeochemical/ic.html Microbial Life (2016)...