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CHEM 115L (Fall 2023) - Rya Al Mubarak 10 - Copper in Water/Data Collection PDF Version generated by Rya Al Mubarak on Dec 05, 2023 @10:32 AM EST Table of Contents Data Collection ....................................................................................................................................................................................................................................................... 2

Data Collection Exp 10 - Copper in Water - Data Collection Kaitlin Bailey - Jul 25, 2018, 9:19 AM EDT 10 - Copper in Water/Data Collection 2 of 9

Lab Partner: abdul yherlies hawkat Date of Experiment: nov 28 2023 Data Collection: Table 1: Exp # Starting Conc (M) Volume pipetted (mL) Volume of H O added (mL) Total Volume (mL) Final Conc(M) 1 5.0 x 10^-2 10 0 10 5.0 x 10^-2 2 5.0 x 10^-2 8 2 10 4.0 x 10^-2 3 5.0 x 10^-2 6 4 10 3.0 x 10^-2 4 5.0 x 10^-2 4 6 10 2.0 x 10^-2 5 5.0 x 10^-2 0 8 10 1.0 x 10^-2 Table 2: Sample Absorbance – Trial 1 Absorbance – Trial 2 Average Absorbance 1 800.2 808.9 804.6 2 834.3 834.3 834.3 3 831.7 861.1 846.4 4 860.2 382.5 621.4 5 381.6 382.5 382.1 Rya Al Mubarak - Dec 05, 2023, 10:27 AM EST 2 10 - Copper in Water/Data Collection 3 of 9

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Unknown # 1 834.3 872.3 853.3 Unknown # 2 382.5 380.8 381.7 Report lambda of the middle known concentration ___861.1_______ Insert screenshot of graph here: Critical Thinking Questions: 1. What are the criteria for the elimination of data points? If any of your points are outliers, do you have any justification for eliminating these data? max 10 - Copper in Water/Data Collection 4 of 9

To decide the elimination of data points we can use z-scores and visual analysis for outliers to determine which data points should be removed. To ensure the accuracy of the results, take in consideration variables such as experimental mistakes and values outside the predicted range. The lambdamax of the middle known concentration (861.1) led the test of absorbance consistency. 2. Once your graph has been approved, discuss with your lab partner two ways that you might go about determining the concentration of an unknown sample using your graph. Record these two approaches in your lab notebook before you leave the lab. (Hint: one way is qualitative and the other quantitative.) Two ways we might go about determining the concentration of an unkown sample is by comparing compare the absorbance values of the unknown sample to the absorbance values of standard samples with known concentrations for a qualitative analysis on our graph. For a quantitative method, use the graph to construct a linear regression equation that correlates absorbance to concentration. Data Analysis Questions: 1. State in words the relationship that you discovered between absorbance and concentration of a copper sulfate solution. Look up the name of this relationship or law on the internet or in a textbook. The relationship between absorbance and concentration follows a pattern in which the absorbance increases as the concentration increases, in other words, the Beer's Law or Beer-Lambert Law. When more of a substance is present, it absorbs more light, and this absorption may be measured using absorbance. 2. Determine the concentration of the unknown copper in the water sample using the two approaches you proposed. Show calculations or graphical analysis to back up your conclusion. Which method did you think is more accurate and why? We used two approaches to determine the unknown copper concentration. First, based on the graph, qualitative, we estimated it to be between 3.0 x 10-2 M and 2.0 x 10-2 M. We then estimated it more exactly as 1.12 x 10-4 M using a math equation from the graph( quantitative) these approaches had varied outcomes. The math one is more precise, and we believe it is better because it provides a particular number, as opposed to the graph guess. Based on the math method, we assume the unknown copper content is around 1.12 x 10-4 M. 10 - Copper in Water/Data Collection 5 of 9

10 - Copper in Water/Data Collection 6 of 9

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3. Was your absorbance value for your unknown in between the values for the highest and lowest absorbance of your 5 standard solutions? What is the potential problem if it is not in this range? 4. Do you think the specific concentrations that you were made were adequate to determine the concentration in question 2? Why do you think is it necessary to spread the points out over the entire range? The concentrations we measured, which ranged from 1.0 x 10-2 M to 5.0 x 10-2 M, were significant in determining copper concentration. To generate an accurate calibration curve, points must be spread across the whole range. This curve helps in the relationship between absorbance and concentration, allowing us to estimate unknown sample concentrations. 5. Could this type of approach be applied to other metal ions in the water sample? If so, what two things would be necessary before you could complete this analysis? Yes, a similar approach can be used to assess various metal ions in a water sample. To begin, standard solutions for each metal ion in a range of concentrations are required to produce a calibration curve for each metal ion. Second, in order to assure reliable finding, you must create a unique analytical procedure for each metal ion. This means altering experimental settings to suit the properties of each metal ion, such as pH. Error Analysis: Make notes in your lab notebook concerning changes made to the original instructions, known errors or mistakes, as well as highly potential errors. These need not be in complete sentences, but should be neat and make sense to anyone who reads them. no errors were observed 10 - Copper in Water/Data Collection 7 of 9

Discussion Questions : 1. Restate the overall premise of this experiment. (What was the most important objective?) The purpose of this experiment is to investigate whether light absorbance can be used to identify a substance, as you and also to quantify a substance, specifically copper ions in a solution. 2. Summarize the results of the experiment, providing the copper concentration of each of your unknown samples. Compare this to the actual concentrations if given. To establish a calibration curve, we performed experiments with copper solutions of varied concentrations and evaluated their absorbance. The maximum absorbance (lambdamax) at the middle known concentration was 861.1. We approximated the copper contents of Unknown #1 and Unknown #2, which had average absorbances of 853.3 and 381.7, using this curve. 3. a) Summarize any discrepancies that occurred in this experiment. This would include changes to the procedure and known errors or mistakes that occurred. If there were no discrepancies, then state this. Never state that there were “no errors,” but rather that “no errors were observed” or something similar. no errors were observed b) A student measures one of the unknown solutions and the absorbance is higher than ANY of the known solutions used to make the original standard curve. The student still wants to include that data point and determine its concentration so how can they correctly go about doing that? If a student discovers that the absorbance of an unknown solution is greater than that of any of the known solutions included in the original standard curve, the data point can still be included. First, they should estimate how absorbance reacts at greater doses to expand the calibration curve. If the absorbance is higher than usual, the unknown solution may need to be diluted to put it within the calibrated range. Re-measuring absorbance after dilution provides for a more accurate estimation of concentration using the expanded calibration curve. Conclusion: Provide the concentration of the copper in your unknown sample and compare to the values provided by your instructor. In our experiment, we measured the absorbance of copper solutions at various concentrations (experiment 1–5). The maximum absorbance (lambdamax) of the middle known concentration was 861.1. Unknown #1 had an average 10 - Copper in Water/Data Collection 8 of 9

absorbance of 853.3 for our unknown samples, indicating a copper concentration. We estimate the concentration to be roughly 0.03 M using our calibration curve. The calculated concentration for Unknown #2 with an average absorbance of 381.7 is around 0.02 M. When we compare these estimations to the reported values (#1: 0.03 M, #2: 0.02 M), we find that our results for the unknown samples are like the given concentrations. 10 - Copper in Water/Data Collection 9 of 9

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