FAS titration lab ch

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1 QUEENS COLLEGE, CHEM 113.1 – SEC# 25146 Final Lab Report: Experiment #10 November 10, 2022 November 17, 2022 Name Partner’s Name Title: Standard Solutions: FAS Titration

2 Objective: To determine standard solutions of both potassium hydrogen phthalate and ferrous ammonium sulfate hexahydrate. Introduction: A standard solution is a solution with a known concentration that has been made using precise methods to guarantee that the molarity is well-understood. A stock solution is a sizable amount of a common reagent that has been accurately prepared to maybe one or two major figures. These stock solutions include the 0.020 M and 0.10 M potassium permanganate solutions. By doing a standardization for each, I may calculate the more precise concentrations. This is required since a lot of common reagents deteriorate with time or are hygroscopic and accumulate more water. As a result, the concentration fluctuates over time in many common reagents. Due to this, the majority of standard solutions are created as needed and only retained for a brief time (ex: 1-2 weeks) before being re-standardized. As long as the chemicals in the other solutions will react with the standard, a standardized solution can be used to quantitatively assess the concentration of the chemicals in other solutions. Utilizing solids that are extremely stable in air is the first way for creating standard solutions. These salts have a high degree of stability, making it possible to weigh them on a balance without worrying that they would gain or lose mass due to oxidation by oxygen in the air or due to the absorption or loss of water from/to the air. The second approach to creating standard solutions is to first create a solution, which is then reacted with a different standard solution. I will create standard solutions of potassium hydrogen phthalate (Week 1) and ferrous ammonium sulfate hexahydrate for this experiment using the first approach (Week 2). Then, in Week 1, I will standardize the approximately 0.10 M sodium hydroxide stock solution using the acid/base reaction between potassium hydrogen phthalate and sodium hydroxide, as well as the approximately 0.020 M potassium permanganate stock solution using the oxidation/reduction reaction between ferrous ammonium sulfate and potassium permanganate (Week 2). Due to its strong hygroscopicity and ability to rapidly absorb water from the air, solid sodium hydroxide cannot be utilized to make a standard solution using the first technique. Additionally, it reacts with atmospheric carbon dioxide and cannot be kept for long periods of time. Since solid potassium permanganate is a potent oxidant and would react with any traces of organic compounds in deionized water, it cannot be used to make a standard solution. The final amount of permanganate in solution won't be known because the concentration of the permanate ion will change during these side reactions. As a result, the second standardization procedure must be used to standardize stock solutions of potassium permanganate solutions and sodium hydroxide solutions. Experimental Procedure Lab 10a: 1. Clean the two burettes thoroughly, then rinse them with distilled water several times. 2. Using a tared, clean, dry beaker, weigh 4 grams (3.9 to 4.1 g) of FAS. Keep track of FAS's precise weight in your notepad. 3. To start dissolving the FAS in the beaker, add 25 mL of pure water. After that, carefully transfer the FAS to the volumetric flask without spilling any of the solution.

3 4. To stabilize the solution, rinse the beaker with two 10 mL aliquots of distilled water and a third 10 mL aliquot of 3M sulfuric acid. This ensures that any FAS sticking to the beaker walls is transferred to the volumetric flask. Add these washings to the volumetric flask, taking cautious not to spill any of the solution. 5. To mix the contents, cover the flask with the lid (or a rubber stopper or parafilm) and invert several times. Continue in this manner until the FAS has entirely vanished. 6. Rinse with a little amount of distilled water, making sure once more that the water drops into the volumetric flask, after removing the lid (or rubber stopper or parafilm). 7. Fill the flask almost to the etched line with distilled water, cover it, and invert it several times to stir the contents. In order to make sure that the entire solution is still within the volumetric flask, remove the flask lid and rinse it once more. 8. Use a clean medicine dropper (or pipette) to add water until the meniscus's bottom reaches the etched line. Once you've finished making the solution, show your volumetric flask to your lab instructor. You would have to start anew if you overfilled your flask. 9. Instructor must sign and approve the data collected. Lab 10b: 1. Carefully clean the two burettes and rinse several times with distilled water. 2. Once the burette has been thoroughly cleaned, rinse it with three 10 mL portions of the solution it can hold (one burette will hold the standard FAS solution and the other will hold the approximately 0.02 M stock potassium permanganate solution [obtain about 100 mL] to be standardized). This time, let some of the solution run through the tip. Place the rinses in the proper garbage bottle for disposal. 3. Verify that the stopcock is shut. Fill the burette with solution until it is close to the top mark while holding it with the top below eye level. Run a small amount of solution out of the bottom while checking the tip for air bubbles. Holding the partially filled burette in a nearly horizontal position, partially open the stopcock, and let the slow flow of liquid to drive the bubble out of the tip are the recommended methods for removing bubbles. 4. Record the initial volume of liquid in each burette while holding the filled burette vertically in a clamp. Always give yourself at least 15 seconds to ensure that the liquid has completely drained from the burette's inner surface before getting a volume reading. 5. Put about 25 mL of the standard FAS solution into a fresh Erlenmeyer flask using the burette containing the FAS solution. In your lab notebook, indicate how much FAS solution was actually used. Add 15 mL of 3 M sulfuric acid gently and with caution to the 25 mL FAS sample in the Erlenmeyer flask. The H+ ions required for the oxidation/reduction reaction are provided by this acid.

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4 6. Place the Erlenmeyer flask on a sheet of white paper under the burette containing the potassium permanganate solution. (The white paper will help in seeing the end point.) 7. Start adding potassium permanganate to the FAS solution, gently and steadily swirling the flask to properly combine the solution. Potassium permanganate can be added in 1 to 2 mL increments. As potassium permanganate is introduced and reacts with iron, at first, brief crimson streaks will form (II). The red hue will last longer gaps between disappearances as the titration progresses. Start adding potassium permanganate in lesser amounts when this develops. The amount of potassium permanganate that should be supplied should decrease the longer the red color lasts. Add potassium permanganate dropwise as you approach the equivalence point. 8. The first permanent pale pink/red tint in the FAS solution indicates the equivalency point. (A color shift that lasts for at least 30 seconds is considered permanent.) When you are close to the equivalence point, wash any potassium permanganate that has splattered onto the Erlenmeyer flask walls or dripped from the burette tip into solution using the wash bottle's distilled water. Before moving forward, show your instructor the color of your final point, which is the flask. 9. If your instructor indicates that you have overshot the equivalence point (i.e., the color of the solution is dark pink or red/purple), add FAS solution from the FAS burette dropwise until the color disappears. Then add potassium permanganate from the other burette dropwise until you have reached the equivalence point. Be sure to record both the volume of FAS added and the volume of potassium permanganate added. 10. Get a brand-new, spotless Erlenmeyer. Refill the burettes and perform the titration once more using more FAS. Data/Results Table 10a: Molar Mass of FAS 392.14 g/mol Mass of FAS 4.029 g Volume of FAS Solution 100 mL Molarity of FAS 0.1027 mol/L

5 Molarity of FAS Calculation: M = n/L n = m / M n = 4.029 g / 392.14 g/mol n = 0.0102743…= 0.01027 mol 100 mL to L conversion 100 mL x 1 L / 1000 mL = 0.100 L M = 0.01027 mol / 0.100 L = 0.1027 mol/L Table 10b: Trial #1 Trial #2 Trial #3 Initial Burette Reading (FAS) 0 mL 0 mL 0 mL Final Burette Reading (FAS) 25 mL 25 mL 25 mL Volume of FAS in Flask 25 mL 25 mL 25 mL Molarity of FAS 0.1027 mol/L 0.1027 mol/L 0.1027 mol/L Initial Burette Reading (KMnO 4 ) 0 mL 0 mL 0 mL Final Burette Reading (KMnO 4 ) 26 mL 27.5 mL 28 mL Volume of KMnO 4 26 mL 27.5 mL 28 mL Concentration of permanganate 0.01975 M 0.01867 M 0.01834 M Molarity of FAS Calculation: M = n/L n = m / M n = 4.029 g / 392.14 g/mol n = 0.0102743…= 0.01027 mol/L Using the equation M 1 V 1 /2 = M 2 V 2 /10 to find the molarity of permanganate, which can be simplified and later arranged to M KMnO 4 = M FAS x V FAS / 5 x V KMnO 4 this represents the FAS and permanganate. - Trial 1: MKMnO 4 = 0.1027 M x 0.025 L / 5 x 0.026 L = 0.01975 M - Trial 2: MKMnO 4 = 0.1027 M x 0.025 L / 5 x 0.0275 L = 0.01867 M - Trial 3: MKMnO 4 = 0.1027 M x 0.025 L / 5 x 0.028 L = 0.01834 M

6 Calculations: Balanced Equation: 2KMnO 4 + 10Fe(NH 4 ) 2 (SO 4 ) 2 ⋅ 6H 2 O + 8H 2 SO 4 → 2MnSO 4 + 5Fe 2 (SO 4 ) 3 + K 2 SO 4 + 10(NH 4 ) 2 SO 4 + 68H 2 O Reduction half balanced reaction: 2KMnO 4 +5e - → MnSO 4 Oxidation half balanced reaction: FeSO 4 (NH 4 ) 2 (SO 4 ) 2 → Fe 2 (SO 4 ) 3 + e - Reducing agent: Fe(NH 4 ) 2 (SO 4 ) ⋅ 6H 2 O Oxidizing agent: KMnO 4 Moles of MnO 4 – in each titration: - In trial 1: The volume of the permanganate is 0.025 L, and the concentration is at 0.01975 M. using and plugging in data from our table it would be 0.026 L x 0.01975 M = 5.135 x 10 -4 moles of permanganate. - In trial 2: 0.0275 L x 0.01867 M = 5.134 x 10 -4 moles of permanganate - In trial 3: 0.028 L x 0.01834 M = 5.135 x 10 -4 moles of permanganate Comparing my initial weight of FAS and by how much I used from it, I used 1.007 g from the 4.029 g. Subtracting them would be, 3.022 g. Now multiplying 1.007 with 3, is 3.021 g. Average molarity of permanganate for 3 trials: 0.01975 M + 0.01867 M + 0.01834 M= 0.05658/ 3 = 0.01886 M. For the three trials that were conducted, my average was 0.01886 M. This would be to the theoretical 0.02 M in the experiment. Percent error: Formula: % error = |experimental – theoretical / theoretical| x 100 Given in the lab manual the is the 0.02 M of the theoretical. | 0.01886 M – 0.02 M / 0.02 M| x 100 = 5.7% Making the percent error 5.7% What is the purpose of using sulfuric acid in this titration?

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7 The purpose of H 2 SO 4 being used in this titration because sulfur’s oxidation state is +6 which is at the highest level it can reach, therefore it can no longer be oxidized, it maintains the medium’s acidity from the strong oxidizing agent that is KMnO 4 and meet the needs of the stoichiometry of the redox reaction that occurred. Post lab questions: 1. Could a solution of iron(III) be titrated with potassium permanganate? Explain. - A solution of iron(III) cannot titrated with potassium permanganate since Fe +3 cannot be more oxidized. Iron(III) would be the oxidizing agent just like the potassium permanganate, as to why it would not function. 2. What is the average concentration of the potassium permanganate solution? - Average concentration is 0.01886 M (calculations shown above) 3. What sources of error would cause variation in your 2 (or 3) determinations of the concentration of potassium permanganate? - There could be certain variations in the concentration of potassium permanganate would be to adding too much of the equivalence point, another way can be not reading well the volumes that are displayed in the burette. Discussion: The results on all three trials were all ideal, carefully adding 1-2 mL of permanganate into the solution, when the flask read at 40 mL, we decided to take the decrease the amount of permanganate that should be released into the solution, slowly we got to the right and ideal color of the FAS solution. Which means that equivalence point was then met successfully. The percent error could be determined by the equivalence point that could be added too much or by not well reading the volume in the burette. Conclusion: Therefore, we can identify this reaction for this lab as a redox reaction. Doing this lab we found out that the purpose of this was to determine the concentration of potassium permanganate from the 0.02 M stock solution, specifically from a stock solution. Knowing what I learned in this lab is important, knowing that any type of reaction is important when it is dealing with stoichiometry. Also, how we must be extremely careful with the equivalence point, adding too many drops after a certain amount can be critical to the end result, making the solution way darker than how it should truly be. References: Kelly, C. V., Liroff, M. G., Triplett, L. D., Leroueil, P. R., Mullen, D. G., Wallace, J. M., Meshinchi, S., Baker, J. R., Orr, B. G., & Banaszak Holl, M. M. (2009). Stoichiometry and Structure of Poly(amidoamine) Dendrimer-Lipid Complexes. ACS nano , 3 (7), 1886 – 1896. Chang, Raymond, and Jason Overby. Chemistry . McGraw-Hill, 2022.