Students are tested for their knowledge of basic titration technique and proper usage of specific-use probes (those used for conductivity, alkalinity, and pH, chloride, nitrate and hardness detection) on Logger Pro software. The purpose of this comprehensive lab is to determine the chemical properties of public drinking water found at four specific locations in the Toledo Ohio area.
Students test the various repertories of this drinking water by subjecting it to the following tests: pH tests, conductivity tests, total and phenolphthalein alkalinity tests, total hardness, chloride tests, and nitrates tests. With respect to the data collected In this lab, students also use conversion factors to calculate the parts per million. Following directions carefully and prudently Is crucial for the success of the experiment and as well to the fact that the testing will be finished during the lab period.
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Tests like these are perform daily by industrial water treatment plant in order to ensure the Toledo such the EPA to report its findings within a written deadline. Obviously reports of water quality that are not up to the government’s standards, (all of the standards will be listed at a later section in the report) will be subjected to further testing and isolated from public access until the standards are met.
This lab mimics the daily routines of employed chemists at these facilities on a smaller scale. Students that chose to enter such profession will be held responsible for using the techniques learned in this lab. Safety Information: Most of the chemicals used in this lab are dangerous. Avoid bodily contact, ingestion or any type of spills. Assume that all of the reagents used in the lab are poisonous.
Rinse the pH probe thoroughly with distilled water. Place the probe into a small beaker that contains one of the two calibration buffer solutions. B. Choose Experiment, Calibrate… , and select the Sensor Setup tab. With the button for Port 1 (or Channel CHI) depressed, confirm or choose the Sensor: pH probe and Calibration: PH. Select the Calibrate tab and click on Calibrate Now. C. Gently stir the buffer with the pH probe. When the voltage reading of the pH probe is stable. Enter the pH value of the buffer solution (read off of the bottle of buffer solution) to the nearest 0. 01 into
Value 1 and press Keep. D. Rinse the probe with Del water and then place it in a small beaker that contains the second calibration solution. When the reading is stable, enter the pH value of the buffer solution to the nearest 0. 01 into Value 2 and press Keep. Press K to store the calibration. E. Check that the calibration worked by placing the probe back into the buffer solution. If the displayed value does not match the value of the buffer, exit out of Logger and reopen the window. The displayed probe in pH 7 buffer until it is later needed. 4. ) Obtain a suitable size of sample to determine the PH. Ml is suitable for this experiment. Measure this amount of sample using a graduated cylinder. Transfer the sample too ml glass beaker. 5. ) Place the pH probe into the beaker containing the sample. Record the pH of the sample on your Data sheet. 6. ) Rinse the probe with Del water and dry it. Immediately place the probe back into the pH buffer. Conductivity Test: 1 . ) The experiment should already be open on the laptop. If not, select the Expo. 14 Conductivity icon that is on the desktop. 2. ) Double check that the switch box is set to 0-Phipps/CM. This corresponds to 0-magma/L TTS (Total Dissolved Solids).
If necessary, you may change this setting to match your sample’s value. A high range standard is available if needed. 3. ) Calibrate the conductivity probe using a two- point calibration. Use the low-and mid-range solutions to perform the calibrations. A. Initiate the calibration procedure in the software b. Place the Conductivity Probe into a standard solution with a low conductivity value (this should be between O – IPPP/CM or O- MGM/L TTS… Say 1 moms/CM). Be sure the entire elongated hole with the electrode surfaces is submerged in the solution ND that there are no air bubbles along the electrode surface.
Wait for the displayed voltage to stabilize. C. Enter the value of the standard solution in the appropriately chosen units. D. Repeat the calibration using the medium conductivity (this is between O – Phipps… Say mass/CM) 4. ) Analyze the sample’s conductivity a. Using a rinsed ml graduated cylinder, measure ml of the sample. B. Transfer this amount to anther clean and dry beaker. C. Place the probe into the beaker containing the sample. D. Wait for the reading to stabilize. Record the conductivity on your data sheet. E. Convert the reading into MGM/L and pimp. Source: Conductivity Probe, Fernier Software and Technology via their website www. Fernier. Com/support/manuals/) Total and Phenolphthalein Alkalinity Tests: 1 . ) Measure 50 ml of your sample in a graduated cylinder. Transfer the sample into a mall volumetric flask. 2. ) Add three to five drops of phenolphthalein solution to you sample. 3. ) Set up a titration apparatus (where the clean burette is clamped too ring stand). 4. ) Obtain about mall of sulfuric acid (HASPS) into a larger beaker. 5. ) Full the burette with HASPS up until a point above the calibration mark (Mol).
Place a waste beaker under the burette. Open the stopcock and release the remaining HASPS to get rid of air bubbles. 6. ) Record the exact concentration of the HASPS into your data sheet. Record the initial burette reading to the nearest 0. 01 ml. Replace the waste beaker with the flask containing the sample. 7. ) Titrate the sample too colorless endpoint. The solution will be barely pink Just before the endpoint of the solution. Add a few drops of 10% tessellate solution to the sample (do this Just before the endpoint of your titration! ) Record the final volume of the HASPS used. A.
Use the mixed indicator brochures green/methyl red) this sample should be green at the beginning and the endpoint should be a yellow-straw color. B. If needed, refill the burette with more HASPS. Record the initial value into your data table. Sample will become colorless and then the next drop should give you the straw color. 8. ) Record the phenolphthalein alkalinity and total alkalinity in militarily and pimp. Total Hardness Test: 1 . ) Obtain ml of your water sample measured on a graduated cylinder. Transfer the sample too mall volumetric flask. 2. ) Add one scoop of Universe indicator to your sample.
The color of the solution should be reddish pink. 3. ) Obtain bout mall of DEED. Record the concentration of your iterant. 4. ) Set up a similar titration thingy. Rinse a burette with Del and then with DEED. 5. ) Fill the burette with DEED up until the calibration mark. Place the waste beaker under the burette. Open the stopcock to remove air bubbles. Record the initial volume of DEED on your data sheet to the nearest 0. 01 ml. 6. ) Titrate the sample until the color of the solution changes to light blue. 7. ) Report the total hardness in militarily and pimp. (Other Sources: Water Chemistry, ANAL ERROR, Kippering, Edith.
CHEMICAL Lab Manual. 2013-2014) Results: pH and POOH values per each sample tested Total alkalinity and phenolphthalein alkalinity Carbonate, Hydroxide, or Bicarbonate alkalinity present? Carbonate, Hydroxide, and or Bicarbonate alkalinity Total Hardness and Non-Carbonate hardness of each sample Nitrates/Chlorides present Conductivity tests per each sample Sample Calculation used in Sample 4: pH: Value collected from pH probe: 6. 42 pH [H+} = (1. Owe-14)/ (3. 8+7) = 2. 6+8 M POOH = -log[OH-] = -log(2. E-8) = 7. 58 Total alkalinity: When a 100. 0 ml sample is titrated with 0. 010 M [HCI], 0. ml acid is the equivalent of 1. 0 pimp Cacao (source). Total Volume of acid titrated (for both phenolphthalein and brochures green methyl red indicators): 5. 21 ml 0. Ml acid/l . 0 pimp Cacao -? 5. 21 ml acid/ x pimp Cacao 52. 1 pimp cacao Phenolphthalein alkalinity: *Due to a shortage in the amount of sample available for immediate testing only ml was used for the titration using phenolphthalein indicator. The calculations below are doubled in order to compensate for variables used in the proportion) * of 1. 0 pimp Cacao (source). Volume of acid titrated: 1. 51 ml 2(o. Ml pimp cacao) = 2(1. 51 ml acid)/xx 5. pimp cacao Carbonate Alkalinity Present? Carbonate alkalinity is present when phenolphthalein alkalinity is not zero, but is less than half of the total alkalinity (source). Half of Total alkalinity = 15. 1/2 = 26. 05 pimp cacaos o 15. 1 pimp cacaos 26. 05 pimp cacao Yes carbonate alkalinity is present because the phenolphthalein value (15. 1 pimp Cacao) is a nonzero number that is less than half of the total alkalinity of the sample (26. 05 pimp Cacao). Carbonate Alkalinity: Carbonate alkalinity = 2 (phenolphthalein alkalinity) = 2(15. 1) pimp (CO)2- = 30. 2 pimp (cacao)2- Anton Hydroxide Alkalinity Present?
Hydroxide alkalinity is present if phenolphthalein alkalinity is more than half of the total alkalinity. 15. 1 pimp cacaos 226. 05 pimp cacaos This statement is false thereby proving that no hydroxide alkalinity is present in this sample of water. Hydroxide alkalinity: N/A Bicarbonate Alkalinity Present? Bicarbonate alkalinity is present if phenolphthalein is less than half of the total alkalinity (source). 15. 1 pimp Cacao 26. 05 pimp Cacao Yes bicarbonate alkalinity is present in this sample because the phenolphthalein alkalinity value (15. 1 pimp Cacao) is less than half of the total alkalinity of the sample 26. 5 pimp Cacao). Bicarbonate Alkalinity: Bicarbonate Alkalinity = T-UP = 21. 9 pimp HCI- Total Hardness of Sample: When a 100. 0 ml sample is titrated with 0. MM DEED, 0. 10 ml of DEED is the equivalent of 1. 0 pimp Cacao (Kippering, Lab Manual). *Due too shortage in the amount of sample available for immediate testing only ml was used for the titration using phenolphthalein indicator. The calculations below are doubled in order to compensate for variables used in the proportion) * Volume of DEED titrated: 5. 25 ml 2(0. 1 ml pimp cacao) = 2(5. 25 ml DEED)/XX pimp cacao x = 52. 5 pimp
Non-Carbonate hardness of the Sample: This is the difference between the Total Hardness and the Total Alkalinity (52. 5 pimp cacao) – (52. 1 pimp cacao) = 0. 4 pimp cacao Observations: Each of the four samples collected were visually similar. Each were colorless, and mostly free of suspended particles. None exhibited any odors. The test done on sample 4 for hardness were dissimilar to the tests done on the previous samples because it form an orange complex with the Universe indicator rather than the more commonly found red color. This may have been due to improper cleaning of glassware.
The phenolphthalein alkalinity test done for sample 3 was peculiar in that addition of large amounts of iterant did not produce a visible endpoint. Upon further investigative assistance from the TA it was confirmed that the water sample was already at its most acidic state recognizable by the phenolphthalein indicator. Discussion: The purpose of this lab was to simulate the government-run procedures done to analyze public drinking water, an important event that is mandated by the Environmental Protection Agency (EPA). Understanding the underlying methods for success at these series of experiments is what the main idea is.
The series requires students to recall and implement various laboratory techniques in order to process the sample of water. It is a comprehensive review on the following: using computer software such as Logger Pro, calibration technique using various specific probes, titration, understanding the basics of geochemistry in chemical expressions, understanding the effects of pH on solutions, and overall safety awareness. Chemists use these techniques to tackle more complex problems. For now, the simpler “mint” experiments listed above are up for discussion. The first experiment done was the total hardness test.
This involves the iterant, DEED which forms a dark red complex with the indicator Universe. Adding this iterant to the sample-indicator mixture causes the red color to fade. This is the result of the unknown metal action in the sample reacting with the DEED and getting rid of the red complex formed. Thus the solution color turns blue, which signals the student that the endpoint has been reached. Essentially the amount of DEED titrated determines the amount of unknown metal present in the sample. These metals are Ca+ and Approximation of the specific action present is heavily reliant upon the pH of the ample water.
If the pH is above 12, then only the Ca+ action can be detected. The total hardness of sample 1 was reported at 119. 9 pimp Cacao. The extent to how hard the water is, is denoted by a scale of water hardness. The scale used here was taken from the Fairfax County Water Authority, a water treatment facility. It states that: soft water has less than 17. 1 pimp of metal particles, slightly hard water has 17. 1 – 60 pimp metal particles, hard water has 120-180 pimp metal particles, and very hard water has over 180 pimp metal ions present (“Explanation of Water Hardness”, www. Face. G The water in sample 1 is therefore moderately hard to hard. Sample 2, 3, and 4 contain slightly hard water. In addition the Non- carbonate hardness was also calculated. The results from both the total and non-carbonate hardness tests for each sample are shown in the graph titled, “Total Hardness and Non-carbonate Hardness of each sample”. The non-carbonate hardness tests accounts for different anions other than the carbonates that may be responsible the presence of dissolved salts in drinking water. Such anions include certain types of sulfates, chlorides, and nitrates (Kippering, Lab Manual).
The non-carbonate hardness of each sample cannot be determined until a full assessment of the total alkalinity of each sample is done. Thus these calculations are held for the third section of this paper. The EPA does not have a standard or hardness of water. In fact, the National Research Council states that hard drinking water generally contributes a small amount of calcium and magnesium human dietary needs (“Explanation of Water Hardness”, www. Face. Org). How can we tell what ions are present in each sample? This is entirely dependent on the relative pH of the samples which is discussed in the next section.
Determining the pH of all four samples is a simple procedure. As long as the pH probe is calibrated using the correct buffers each determination should give an accurate result. PH is a measure of the concentration of protons (H+) in a sample. Solutions containing large exponentially small concentration of hydrogen ion give a large value pH and the opposite is true for higher concentrations. This phenomenon occurs because measurement of pH is measured on a logarithmic scale. The pH values given by the computer can be converted into hydrogen ion concentrations by taking the negative log of the pH of the sample.
Chemists use the ion- product of water theory to convert hydrogen ion concentration to hydroxide ion (OH-) concentration. Simple use the equation: K = [HUH+] *[H+] and [HUH+] can be used interchangeably Using these equations students can effortlessly convert the pH of their samples into their corresponding hydroxide concentrations as noted in the graph titled, “pH and POOH values per each sample tested,” The pH of sample 1 is 5. 5, which is highly acidic. Sample 2 has a pH of 6. 02. Sample 3 has a pH of 6. 49, whereas sample 4 has a pH of 6. 42 all of the samples tested here contained slightly acidic eater.
The EPA does not have a standard for pH because it is considered a secondary drinking water contaminant, which is aesthetic (pH, www. Odd. Ohio. Gob). Although the EPA does not regulate this property of water, the Ohio Department of Health does provide additional causes and effects of unnatural pH levels. They claim that the our water, the soil composition that the surface water runs though and a host of others (pH, www. Odd. Ohio. Gob). These causes are most relevant as they have a direct impact on the quality of our drinking water, which comes primarily from surface waters.
As a result from continued use of basic water (pH above 7) people report bitter tasting water, and buildup of minerals in plumbing (pH, www. Odd. Ohio. Gob). As a result from continued use of acidic water, residents will have sour tasting water, and metallic staining (pH, www. Odd. Ohio. Gob). Extreme cases will undoubtedly cause bodily harm Just as the reagent used in lab. As stated earlier, both calcium and magnesium ions can be detected in samples at a pH lower than 12. Since all of the tested sample have lower pH values, we can conclude that there are both calcium and magnesium ions present.
The following experiment tested each sample for total and phenolphthalein alkalinity. Alkalinity is a measure f the amount of basic ions in a sample (Kippering, Lab Manual). The procedure for alkalinity is titration. Students find the phenolphthalein alkalinity first by titrating the sample with the phenolphthalein indicator to a clear endpoint and recording the amount of iterant (HCI) used. A second indicator, (brochures green methyl red) is added to the sample and further titrated to a straw yellow color. Students use the amount of HCI added in the first titration to calculate the phenolphthalein alkalinity.
Then they use the total amount of HCI titrated to calculate the total alkalinity. The following expression was used to calculate all of the entries for total and phenolphthalein alkalinity: when a 100. 0 ml sample is titrated with 0. 010 M [HCI], 0. 10 ml acid is the equivalent of 1. 0 pimp Cacao (Kippering, Lab Manual). Each calculation can be seen in the graphs titled, “Total alkalinity and Phenolphthalein alkalinity’. All of the measurements are calculated in pimp Cacao. Sample 1 produced a phenolphthalein alkalinity of pimp Cacao and a total alkalinity of 181 pimp Cacao.
Sample 2 reduced a phenolphthalein alkalinity of O pimp Cacao and a total alkalinity of 18. 9 pimp Cacao Sample three gave a phenolphthalein alkalinity of 10 pimp Cacao and a total alkalinity of 54 pimp Cacao. Lastly Sample 4 gave a phenolphthalein alkalinity of 15. 1 pimp Cacao and a total alkalinity of 52. 1 pimp Cacao. In addition to these two measurements, students were also required to calculate the carbonate, hydroxide, and bicarbonate alkalinity if at all present in the samples. The results table for these variables are found under the table titled, “Carbonate, Hydroxide, or Bicarbonate alkalinity present?
If the samples met a certain criteria, then they tested positive for the three possible alkalinity’s. Students could then use the three equations listed in their procedure and calculations sheet to calculate the alkalinity of the corresponding anion present. A trend can be note in the tables above. Samples that had no hydroxide alkalinity tested positive for carbonate and bicarbonate alkalinity respectively. Samples 3 and 4 both shared carbonate and bicarbonate alkalinity. Thus sources of carbonate solids are the main contributors to their alkalinity. Sample 1 is the only one that is positive for hydroxide alkalinity.
Thus salts of hydroxide must be the main contributor to its alkalinity. PH and alkalinity are treated similarly by the EPA, as they are both regarded as secondary standards. They are not regulated. In general alkalinity is treated much the same as basic solutions are. Total alkalinity is needed to calculate the non-carbonate hardness. Now the values for total alkalinity done. Students simply subtract the total hardness by the total alkalinity. The values given show the amount of dissolved solids that are not carbonates (such as sulfate, nitrate and chloride salts). The last three tests are the most simple.
They involve the usage of specific probes Just as in the experiment for pH determination. The next experiment tested the conductivity of the four samples. Conductivity is a measurement of electrical activity in a sample. After proper calibration of the software, students place the conductivity probe into the sample and enter the value on the data sheet. The standard value of water conductivity is given in as/CM. All of the entries for the four samples are located under the table titled, “Conductivity tests per each sample,” Distilled water has a conductivity of about 0. as/CM to 3 as/CM whereas many rivers along the U. S. Have conductivities as large as 50 to 1500 as/CM (Conductivity, water. EPA. Gob). The results from the four samples tested show that the drinking water in the Toledo area is much similar to that of the water in all of the U. S. Waterways. The high voltage could be due to the dense population of dissolved ions present in each sample. Such quantities could produce a small electrical gradient. The very last two experiments were Just like the last experiment. This time students tested their sample for nitrates and chlorides present.
A nitrate-specific probe was seed for the nitrate analysis and the chloride specific probe was used or the chloride analysis. After properly calibrating the probes, students immersed the probes into each sample at a time and collected the data displayed on the computer. The entries for these two experiments are located below the table titled, “Nitrates/Chlorides present”. Each value is expressed using the standard units of MGM/L. According to the Ohio EPA, the standard amount or nitrates in public water is MGM/L (Water Quality Standards Program, www. EPA. Tate. Oh. Us). A value higher than this standard violates he sanctions set forth by the EPA and leads to further investigation of the problematic water. Each of the four samples had a value much less than the standard, proving that the public drinking water from the Toledo are is partially free from nitrates. Why are nitrates so bad? We must look way back to the original source of our drinking water- surface water. Surface waters from rivers and lakes can easily become tainted with contaminants such as pesticides, wastes, and fertilizers (rich in nitrates).
Although presence of nitrate to us may not be a bad thing to us, it most certainly is to the environment. Sudden increase in such nutrient bound runoff causes extreme algal blooms consume large amounts of oxygen in the water. This in turn suffocates aquatic organisms. And pesticide in our drinking water obviously poses as a health concern. The maximum amount of chloride allowed in public drinking water is OMG/L according to the United States EPA (“Basic Information about Disinfectants in Drinking Water: Chlorine, Chlorine and Chlorine Dioxide”,water. Pa. Gob). All four samples abide by this regulatory standard. If the opposite had occurred the government would shut off the publics access to this eater. The chloride ion is very reactive, so in nature it is usually found attached to a group IA or AAA metal or to itself. By itself it can become dangerous. Error Analysis The probability of human error for this series of experiment is multiplied due to Mistakes were undoubtedly made; solutions were over-titrated, and probes were used that were not calibrated properly.
One such example of human error is the source of the large difference between sample Xi’s total alkalinity compared to the other three samples. This is a sign that a student over-titrated the solution. This exults in a volume of hydrochloric acid titrated that is larger than the actual value needed. Thus alkalinity value is higher because the calculation shows that a larger amount of acid was needed to neutralize the water sample. It gives the false impression that the sample was very alkaline/basic to begin with.
To fix this, students should add iterant by the ml until resistance to color change takes longer, then add drop wise. Calibration of the probes was always an issue. Although the samples tested positive for the standards governed by the Environmental Protection agency, the results from the conductivity tests were a little high. Thus to FL this problem, he probes must be properly calibrate. To properly calibrate a probe means to immerse he sensitive head into the solution (so the small white dot is Just below the liquid surface) and enter the value of the corresponding standard into the computer.
The one step that catches mot students is the waiting time. Impatience lead to improper calibration. Cross contamination of the probes by dipping them in the samples without cleaning them with denizen water and wiping them off with a clean towel could also have adversely affected the results from the experiment. Misinterpreting he values displayed on measurement instruments such as the graduated cylinder and the values on the computer could have led to tremendous error. Misuse of significant figures was a drawback caused by both the student and the computer.
This applies mostly to the calculation of hydrogen ions and hydroxide ions from pH values. The computer at lab showed pH values using both two one and two significant figures. Constant rounding up of number during calculations ay have alter the actual value of the hydroxide concentration slightly. Conclusion: The purpose of this series of experiment was to provide students a real-life application of nearly all of the techniques they have learned in their first year of general chemistry lab.
The concept of the entire procedure was to show student how certain chemical species (like dissolved actions, anion, and organisms perhaps) interact in aqueous solution. The results from the series of experiments show that the various techniques used in college lab are similar to the ones used by employed chemists in water treatment plant. Where’s the proof? Well by looking at the results from this lab and comparing them to the standards produced by the Environmental Protection Agency, one could say that they are quite similar.