Stoichiometry lab report

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Marquette University *

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1001

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Chemistry

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Feb 20, 2024

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CHEM 1001 STOICHIOMETRY Laboratory Report NAME : Liam Cedeno Agosto DATE : 3/28/23 SECTION : 403 TA : Audrey Vice A. Goals/Purpose of Experiment ( 2 Points, ~50 words ) : The purpose of this experiment was to take the stoichiometry of a reaction and from that understand limiting reactants. To do this, we must also learn to use graphical analysis to figure out the ratio of the metal and ligand ion in this experiment. B. Theory/Introduction ( 6 Points, ~100 words ) : Balancing equations is an important part of chemical reactions, from that we can determine the mole ratio of a reactant and a product. This is called stoichiometry. More specifically, stoichiometry has to do with the calculations of the masses or volumes of the reactants of a chemical reaction. For this lab, we used two methods to determine the absorbance of a metal and ligand ion solution to ultimately find the mole ratio. These methods are Job ’ s method and mole ratio method. C. Procedure summary ( 5 Points, ~100 words ) : This experiment consisted of two parts. Part one consisted of Job ’ s method, where the total volume of the reactants is kept constant. In two burets, one with the metal solution and one with the ligand, we were to take increasing amounts of each solution into a 10 mL volumetric flask, starting from 0.50 of the metal and 4.50 of the ligand. The final volume was set to 10 mL using deionized water. From there, each solution was transferred onto a test tube, and from there we were to find the absorbance using a measure net station. The second part consisted of mole ratio method where the volume of ligand is kept constant at 5.00 mL for each test tube. And the volume of metal was increased by 0.50 increments for nine test tubes starting at 0.50. The same procedure as part one is followed. D. Results and Calculations: ( 12 Points ) :

Part 1: Job’s Method You can use this tutorial if you need help with the calculations. Copy and paste the link in your browser if clicking doesn’t work https://youtu.be/aket03N6jJA . Initial metal ion solution buret reading (mL) = 5.68 mL Initial ligand solution buret reading (mL) = 12.28 mL Table 1: Job ’ s method Test tube # Metal ion solution buret reading (mL) Volume of metal ion solution (mL) Ligand solution buret reading (mL) Volume of ligand solution (mL) Absorbance 1 5.68 0.50 12.28 4.5 0.373 2 6.78 1.00 16.39 4 0.619 3 8.28 1.50 19.86 3.50 0.617 4 10.29 2.00 22.89 3.00 0.490 5 12.91 2.50 25.7 2.50 0.607 6 15.91 3.00 27.72 2.00 0.377 7 19.42 3.50 29.25 1.50 0.277 8 23.39 4.00 30.25 1.00 0.213 9 27.85 4.50 30.77 0.50 0.096

Volume of metal ion at the intersection point = 1.52 mL Volume of ligand at the intersection point = 3.48 mL Moles of metal ion = 1.52 x 10^-6 Moles of ligand = 4.872 x 10^-6 Mole ratio (n) = 3.2=~ 3 Part 2: Mole Ratio Method Initial metal ion solution buret reading (mL) = 13. 54 mL Initial ligand solution buret reading (mL) = 20.91 Table 2: Mole ratio Test tube # Metal ion solution buret reading (mL) Volume of metal ion solution (mL) Ligand solution buret reading (mL) Volume of ligand solution (mL) Absorbance 1 13.54 0.50 20.91 5.00 0.370 2 14.59 1.00 25.94 5.00 0.629 3 16.08 1.50 30.95 5.00 0.784 4 18.08 2.00 35.97 5.00 0.899 5 20.59 2.50 40.99 5.00 0.835 6 23.59 3.00 19.88 5.00 0.843 7 26.55 3.50 24.82 5.00 0.797 8 30.61 4.00 29.81 5.00 0.880 9 32.15 4.50 32.84 5.00 0.832

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Volume of the metal ion at the intersection point = 1.66 mL Volume of ligand at the intersection point = 5.00 mL Moles of metal ion = 1.66 x 10^-6 mol Moles of ligand = 7.0 x 10^-6 mol Mole ratio (n) = 4.2~= 4 Demonstrated Calculations: Show the calculations for Part 1 and part 2 of this lab. Part 1 Volume of metal ion at intersection point= 0.244x + 0.2923 = -0.1858x + 0.9473= 1.52 mL Volume of ligand = 5.00 mL – 1.52 mL= 3.48 mL Moles of metal ion= 0.001 M x 0.00152 L = 1.52 x 10^-6 mol Moles of ligand= 0.0014 M x 0.00348 L = 4.872 x 10^-6 mol Mole ratio= 4.872 x 10^-6/1.52 x 10^-6 = 3.2=~ 3 Part 2

Volume of metal ion at intersection point = 0.414x + 0.1803 = -0.0141x + 0.8934= 1.66 mL Volume of ligand at intersection point= 5.00 mL Moles of metal ion = 0.001 M x 0.00166 L = 1.66 x 10^-6 mol Moles of ligand = 0.0014 M x 0.005 L= 7.0 x 10^-6 mol Mole ratio= 7.0 x 10^-6/1.66 x 10^-6 = 4.2 ~= 4 E. Discussion ( 10 Points ) : 1. Look at the two graphs that you made. Identify the limiting reagent before , after, and at the intersection point in each method. ( 4 points ) 2. Discuss the basic differences between the mole ratio and Job’s method. ( 2 points ) The biggest difference between the mole ratio and Job ’ s method is simply the constant of each. In mole ratio, the volume of the ligand is the constant, meaning it stayed the same throughout, whereas in Job ’ s method, the constant was the total volume of the reactants. 3. How does this lab complement your understanding of the concept of Stoichiometry? ( 2 points ) It allowed me to have a better understanding in how limiting and excess agents contribute overall to determining the mole ratio of a chemical reaction, which is the overall purpose of stoichiometry. 4. Discuss the possible sources of error in this experiment and how they could be minimized. ( 2 points ) Based on my results, the biggest source of error that can be easily made and should be minimized would be the mole ratio. The mole ratio should be the same for both methods. That was not the case for my experiment. That must have been due to an error in my measurements in the mole ratio method. I did not measure my numbers accurately to save time and approximated some decimals when I couldn ’ t determine for certain. Estimating, in this experiment should be minimized to minimize errors in later calculations.

F. Conclusions ( 5 Points, ~100-150 words ) : Overall, I believe I was successful in the overall sense of understanding how absorbance relates to finding the mole ratio of a chemical equation, which plays into the concept of stoichiometry. I also believe I succeeded at the graphical analysis part, and how that also plays a role. However, the actual result of this was not as accurate as it could ’ ve been, which was due to my lack of consistency during my observations and taking my measurements. My measurements weren ’ t consistent, which probably impacted my data and ultimately my calculations.

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