Skills Challenge 2- Determination of Unknown Concentrations Post lab submission

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Worcester Polytechnic Institute *

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1022

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Chemistry

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Feb 20, 2024

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pdf

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Skills Challenge 2 Determination of Unknown Dye Concentration – Post Lab Submission Names and Contributions: (list all team members and their contributions using the CRediT system outlined in the Teamwork Module: Listing Contributions on Assignments. Make sure to indicate the corresponding author as the one who submits the assignment.) Taylor Hamilton: Author, Conceptualization, Analysis, Data Curation, Writing - Original Draft, Writing - Review & Editing Tyler Deal: Methodology, Investigation, Visualization, Writing – original draft, Writing – Review and editing Ryan Magner: Data Curation, Investigation, Analysis, Methodology, Writing – original draft, Writing – Review and editing Description of the unknown: clear blue liquid List each measuring device used and state its uncertainty: (For example, 50-mL volumetric flask – uncertainty  0.05 mL) • 5-mL graduated cylinder  0.05mL • 25-mL volumetric flasks ±0.05 cm Method: ( Be concise and comprehensive, use grammatically correct complete sentences in past tense, passive voice, paragraph format) The unknown dye was found via a systematic approach that included numerous steps. Initially, the known dye stock with 0.500 ppm was diluted several times for the first dilution 4ml of the stock dye was added to a 5 mL graduated cylinder then the rest of the cylinder was filled up with water to the 5 mL marker. This combined solution was now 80% concentration. Next, 3mL of the stock dye was poured into a 5 mL graduated cylinder, and the remainder of the cylinder was filled with water to the 5 mL marker, resulting in a 60% concentration. 2mL of the stock dye was poured into a 5 mL graduated cylinder, and the remainder of the cylinder was filled with water to the 5 mL marker, yielding a 40% concentration. 1mL of the stock dye was poured into a 5 mL graduated cylinder, and the remainder of the cylinder was filled with water to the 5 mL marker, yielding a 20% concentration. These concentrations were then put into cuvettes. Two other cuvettes were filled, one with water, and one with just the stock dye. One more cuvette was filled with a 50/50 solution of the unknown dye and water using the previous method. Then all the cuvettes are run through a spectrometer to determine the absorption value of each. Each abs value had to be below 1 or the results would be

inaccurate. A graph was created using the determined abs values and dilutions to calculate the rest of the results. Results: (Include data table(s) for property measured in identifying the concentration in the unknown sample. Show data for solutions used to obtain the standard curve and the unknown.) Table 1 : Percent Dilutions of Stock Dye and Unknown Dye plus their Absorption Values Percent Dilutions of Stock Dye Absorption Values 100% 0.9067 80% 0.7098 60% 0.5210 40% 0.4462 20% 0.1704 Percent Dilution of Unknown Dye Concentration Absorption Value 50% 0.8199 What is the independent variable? % dilutions of solutions What is the dependent variable? Absorption value Include the standard curve (including equation and R 2 ) generated from Excel (or other graphing software): Absorption Values of Different Dilutions Figure 1: This graph depicts the mostly linear increase in absorption values as percent dilutions increase to 100%. As well as the equation for the trend line and a R^2 value close to 1.

Show the calculation of unknown concentration using standard curve (include average): ? = 0.0087? + 0.03 0.8199 = 0.0087? + 0.03 0.8199 − 0.03 = 0.0087? 0.7899 0.0087 = ? ? = 90.793 Concentration of unknown solution: 90.793

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